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1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * async.c
4 : : * Asynchronous notification: NOTIFY, LISTEN, UNLISTEN
5 : : *
6 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
7 : : * Portions Copyright (c) 1994, Regents of the University of California
8 : : *
9 : : * IDENTIFICATION
10 : : * src/backend/commands/async.c
11 : : *
12 : : *-------------------------------------------------------------------------
13 : : */
14 : :
15 : : /*-------------------------------------------------------------------------
16 : : * Async Notification Model as of v19:
17 : : *
18 : : * 1. Multiple backends on same machine. Multiple backends may be listening
19 : : * on each of several channels.
20 : : *
21 : : * 2. There is one central queue in disk-based storage (directory pg_notify/),
22 : : * with actively-used pages mapped into shared memory by the slru.c module.
23 : : * All notification messages are placed in the queue and later read out
24 : : * by listening backends. The single queue allows us to guarantee that
25 : : * notifications are received in commit order.
26 : : *
27 : : * Although there is only one queue, notifications are treated as being
28 : : * database-local; this is done by including the sender's database OID
29 : : * in each notification message. Listening backends ignore messages
30 : : * that don't match their database OID. This is important because it
31 : : * ensures senders and receivers have the same database encoding and won't
32 : : * misinterpret non-ASCII text in the channel name or payload string.
33 : : *
34 : : * Since notifications are not expected to survive database crashes,
35 : : * we can simply clean out the pg_notify data at any reboot, and there
36 : : * is no need for WAL support or fsync'ing.
37 : : *
38 : : * 3. Every backend that is listening on at least one channel registers by
39 : : * entering its PID into the array in AsyncQueueControl. It then scans all
40 : : * incoming notifications in the central queue and first compares the
41 : : * database OID of the notification with its own database OID and then
42 : : * compares the notified channel with the list of channels that it listens
43 : : * to. In case there is a match it delivers the notification event to its
44 : : * frontend. Non-matching events are simply skipped.
45 : : *
46 : : * 4. The NOTIFY statement (routine Async_Notify) stores the notification in
47 : : * a backend-local list which will not be processed until transaction end.
48 : : *
49 : : * Duplicate notifications from the same transaction are sent out as one
50 : : * notification only. This is done to save work when for example a trigger
51 : : * on a 2 million row table fires a notification for each row that has been
52 : : * changed. If the application needs to receive every single notification
53 : : * that has been sent, it can easily add some unique string into the extra
54 : : * payload parameter.
55 : : *
56 : : * When the transaction is ready to commit, PreCommit_Notify() adds the
57 : : * pending notifications to the head of the queue. The head pointer of the
58 : : * queue always points to the next free position and a position is just a
59 : : * page number and the offset in that page. This is done before marking the
60 : : * transaction as committed in clog. If we run into problems writing the
61 : : * notifications, we can still call elog(ERROR, ...) and the transaction
62 : : * will roll back safely.
63 : : *
64 : : * Once we have put all of the notifications into the queue, we return to
65 : : * CommitTransaction() which will then do the actual transaction commit.
66 : : *
67 : : * After commit we are called another time (AtCommit_Notify()). Here we
68 : : * make any required updates to the effective listen state (see below).
69 : : * Then we signal any backends that may be interested in our messages
70 : : * (including our own backend, if listening). This is done by
71 : : * SignalBackends(), which sends a PROCSIG_NOTIFY_INTERRUPT signal to
72 : : * each relevant backend, as described below.
73 : : *
74 : : * Finally, after we are out of the transaction altogether and about to go
75 : : * idle, we scan the queue for messages that need to be sent to our
76 : : * frontend (which might be notifies from other backends, or self-notifies
77 : : * from our own). This step is not part of the CommitTransaction sequence
78 : : * for two important reasons. First, we could get errors while sending
79 : : * data to our frontend, and it's really bad for errors to happen in
80 : : * post-commit cleanup. Second, in cases where a procedure issues commits
81 : : * within a single frontend command, we don't want to send notifies to our
82 : : * frontend until the command is done; but notifies to other backends
83 : : * should go out immediately after each commit.
84 : : *
85 : : * 5. Upon receipt of a PROCSIG_NOTIFY_INTERRUPT signal, the signal handler
86 : : * sets the process's latch, which triggers the event to be processed
87 : : * immediately if this backend is idle (i.e., it is waiting for a frontend
88 : : * command and is not within a transaction block. C.f.
89 : : * ProcessClientReadInterrupt()). Otherwise the handler may only set a
90 : : * flag, which will cause the processing to occur just before we next go
91 : : * idle.
92 : : *
93 : : * Inbound-notify processing consists of reading all of the notifications
94 : : * that have arrived since scanning last time. We read every notification
95 : : * until we reach either a notification from an uncommitted transaction or
96 : : * the head pointer's position.
97 : : *
98 : : * 6. To limit disk space consumption, the tail pointer needs to be advanced
99 : : * so that old pages can be truncated. This is relatively expensive
100 : : * (notably, it requires an exclusive lock), so we don't want to do it
101 : : * often. We make sending backends do this work if they advanced the queue
102 : : * head into a new page, but only once every QUEUE_CLEANUP_DELAY pages.
103 : : *
104 : : * 7. So far we have not discussed how backends change their listening state,
105 : : * nor how notification senders know which backends to awaken. To handle
106 : : * the latter, we maintain a global channel table (implemented as a dynamic
107 : : * shared hash table, or dshash) that maps channel names to the set of
108 : : * backends listening on each channel. This table is created lazily on the
109 : : * first LISTEN command and grows dynamically as needed. There is also a
110 : : * local channel table (a plain dynahash table) in each listening backend,
111 : : * tracking which channels that backend is listening to. The local table
112 : : * serves to reduce the number of accesses needed to the shared table.
113 : : *
114 : : * If the current transaction has executed any LISTEN/UNLISTEN actions,
115 : : * PreCommit_Notify() prepares to commit those. For LISTEN, it
116 : : * pre-allocates entries in both the per-backend localChannelTable and the
117 : : * shared globalChannelTable (with listening=false so that these entries
118 : : * are no-ops for the moment). It also records the final per-channel
119 : : * intent in pendingListenActions, so post-commit/abort processing can
120 : : * apply that in a single step. Since all these allocations happen before
121 : : * committing to clog, we can safely abort the transaction on failure.
122 : : *
123 : : * After commit, AtCommit_Notify() runs through pendingListenActions and
124 : : * updates the backend's per-channel listening flags to activate or
125 : : * deactivate listening. This happens before sending signals.
126 : : *
127 : : * SignalBackends() consults the shared global channel table to identify
128 : : * listeners for the channels that the current transaction sent
129 : : * notification(s) to. Each selected backend is marked as having a wakeup
130 : : * pending to avoid duplicate signals, and a PROCSIG_NOTIFY_INTERRUPT
131 : : * signal is sent to it.
132 : : *
133 : : * 8. While writing notifications, PreCommit_Notify() records the queue head
134 : : * position both before and after the write. Because all writers serialize
135 : : * on a cluster-wide heavyweight lock, no other backend can insert entries
136 : : * between these two points. SignalBackends() uses this fact to directly
137 : : * advance the queue pointer for any backend that is still positioned at
138 : : * the old head, or within the range written, but is not interested in any
139 : : * of our notifications. This avoids unnecessary wakeups for idle
140 : : * listeners that have nothing to read. Backends that are not interested
141 : : * in our notifications, but cannot be directly advanced, are signaled only
142 : : * if they are far behind the current queue head; that is to ensure that
143 : : * we can advance the queue tail without undue delay.
144 : : *
145 : : * An application that listens on the same channel it notifies will get
146 : : * NOTIFY messages for its own NOTIFYs. These can be ignored, if not useful,
147 : : * by comparing be_pid in the NOTIFY message to the application's own backend's
148 : : * PID. (As of FE/BE protocol 2.0, the backend's PID is provided to the
149 : : * frontend during startup.) The above design guarantees that notifies from
150 : : * other backends will never be missed by ignoring self-notifies.
151 : : *
152 : : * The amount of shared memory used for notify management (notify_buffers)
153 : : * can be varied without affecting anything but performance. The maximum
154 : : * amount of notification data that can be queued at one time is determined
155 : : * by the max_notify_queue_pages GUC.
156 : : *-------------------------------------------------------------------------
157 : : */
158 : :
159 : : #include "postgres.h"
160 : :
161 : : #include <limits.h>
162 : : #include <unistd.h>
163 : : #include <signal.h>
164 : :
165 : : #include "access/parallel.h"
166 : : #include "access/slru.h"
167 : : #include "access/transam.h"
168 : : #include "access/xact.h"
169 : : #include "catalog/pg_database.h"
170 : : #include "commands/async.h"
171 : : #include "common/hashfn.h"
172 : : #include "funcapi.h"
173 : : #include "lib/dshash.h"
174 : : #include "libpq/libpq.h"
175 : : #include "libpq/pqformat.h"
176 : : #include "miscadmin.h"
177 : : #include "storage/dsm_registry.h"
178 : : #include "storage/ipc.h"
179 : : #include "storage/lmgr.h"
180 : : #include "storage/procsignal.h"
181 : : #include "tcop/tcopprot.h"
182 : : #include "utils/builtins.h"
183 : : #include "utils/dsa.h"
184 : : #include "utils/guc_hooks.h"
185 : : #include "utils/memutils.h"
186 : : #include "utils/ps_status.h"
187 : : #include "utils/snapmgr.h"
188 : : #include "utils/timestamp.h"
189 : :
190 : :
191 : : /*
192 : : * Maximum size of a NOTIFY payload, including terminating NULL. This
193 : : * must be kept small enough so that a notification message fits on one
194 : : * SLRU page. The magic fudge factor here is noncritical as long as it's
195 : : * more than AsyncQueueEntryEmptySize --- we make it significantly bigger
196 : : * than that, so changes in that data structure won't affect user-visible
197 : : * restrictions.
198 : : */
199 : : #define NOTIFY_PAYLOAD_MAX_LENGTH (BLCKSZ - NAMEDATALEN - 128)
200 : :
201 : : /*
202 : : * Struct representing an entry in the global notify queue
203 : : *
204 : : * This struct declaration has the maximal length, but in a real queue entry
205 : : * the data area is only big enough for the actual channel and payload strings
206 : : * (each null-terminated). AsyncQueueEntryEmptySize is the minimum possible
207 : : * entry size, if both channel and payload strings are empty (but note it
208 : : * doesn't include alignment padding).
209 : : *
210 : : * The "length" field should always be rounded up to the next QUEUEALIGN
211 : : * multiple so that all fields are properly aligned.
212 : : */
213 : : typedef struct AsyncQueueEntry
214 : : {
215 : : int length; /* total allocated length of entry */
216 : : Oid dboid; /* sender's database OID */
217 : : TransactionId xid; /* sender's XID */
218 : : int32 srcPid; /* sender's PID */
219 : : char data[NAMEDATALEN + NOTIFY_PAYLOAD_MAX_LENGTH];
220 : : } AsyncQueueEntry;
221 : :
222 : : /* Currently, no field of AsyncQueueEntry requires more than int alignment */
223 : : #define QUEUEALIGN(len) INTALIGN(len)
224 : :
225 : : #define AsyncQueueEntryEmptySize (offsetof(AsyncQueueEntry, data) + 2)
226 : :
227 : : /*
228 : : * Struct describing a queue position, and assorted macros for working with it
229 : : */
230 : : typedef struct QueuePosition
231 : : {
232 : : int64 page; /* SLRU page number */
233 : : int offset; /* byte offset within page */
234 : : } QueuePosition;
235 : :
236 : : #define QUEUE_POS_PAGE(x) ((x).page)
237 : : #define QUEUE_POS_OFFSET(x) ((x).offset)
238 : :
239 : : #define SET_QUEUE_POS(x,y,z) \
240 : : do { \
241 : : (x).page = (y); \
242 : : (x).offset = (z); \
243 : : } while (0)
244 : :
245 : : #define QUEUE_POS_EQUAL(x,y) \
246 : : ((x).page == (y).page && (x).offset == (y).offset)
247 : :
248 : : #define QUEUE_POS_IS_ZERO(x) \
249 : : ((x).page == 0 && (x).offset == 0)
250 : :
251 : : /* choose logically smaller QueuePosition */
252 : : #define QUEUE_POS_MIN(x,y) \
253 : : (asyncQueuePagePrecedes((x).page, (y).page) ? (x) : \
254 : : (x).page != (y).page ? (y) : \
255 : : (x).offset < (y).offset ? (x) : (y))
256 : :
257 : : /* choose logically larger QueuePosition */
258 : : #define QUEUE_POS_MAX(x,y) \
259 : : (asyncQueuePagePrecedes((x).page, (y).page) ? (y) : \
260 : : (x).page != (y).page ? (x) : \
261 : : (x).offset > (y).offset ? (x) : (y))
262 : :
263 : : /* returns true if x comes before y in queue order */
264 : : #define QUEUE_POS_PRECEDES(x,y) \
265 : : (asyncQueuePagePrecedes((x).page, (y).page) || \
266 : : ((x).page == (y).page && (x).offset < (y).offset))
267 : :
268 : : /*
269 : : * Parameter determining how often we try to advance the tail pointer:
270 : : * we do that after every QUEUE_CLEANUP_DELAY pages of NOTIFY data. This is
271 : : * also the distance by which a backend that's not interested in our
272 : : * notifications needs to be behind before we'll decide we need to wake it
273 : : * up so it can advance its pointer.
274 : : *
275 : : * Resist the temptation to make this really large. While that would save
276 : : * work in some places, it would add cost in others. In particular, this
277 : : * should likely be less than notify_buffers, to ensure that backends
278 : : * catch up before the pages they'll need to read fall out of SLRU cache.
279 : : */
280 : : #define QUEUE_CLEANUP_DELAY 4
281 : :
282 : : /*
283 : : * Struct describing a listening backend's status
284 : : */
285 : : typedef struct QueueBackendStatus
286 : : {
287 : : int32 pid; /* either a PID or InvalidPid */
288 : : Oid dboid; /* backend's database OID, or InvalidOid */
289 : : ProcNumber nextListener; /* id of next listener, or INVALID_PROC_NUMBER */
290 : : QueuePosition pos; /* backend has read queue up to here */
291 : : bool wakeupPending; /* signal sent to backend, not yet processed */
292 : : bool isAdvancing; /* backend is advancing its position */
293 : : } QueueBackendStatus;
294 : :
295 : : /*
296 : : * Shared memory state for LISTEN/NOTIFY (excluding its SLRU stuff)
297 : : *
298 : : * The AsyncQueueControl structure is protected by the NotifyQueueLock and
299 : : * NotifyQueueTailLock.
300 : : *
301 : : * When holding NotifyQueueLock in SHARED mode, backends may only inspect
302 : : * their own entries as well as the head and tail pointers. Consequently we
303 : : * can allow a backend to update its own record while holding only SHARED lock
304 : : * (since no other backend will inspect it).
305 : : *
306 : : * When holding NotifyQueueLock in EXCLUSIVE mode, backends can inspect the
307 : : * entries of other backends and also change the head pointer. They can
308 : : * also advance other backends' queue positions, unless the other backend
309 : : * has isAdvancing set (i.e., is in process of doing that itself).
310 : : *
311 : : * When holding both NotifyQueueLock and NotifyQueueTailLock in EXCLUSIVE
312 : : * mode, backends can change the tail pointers.
313 : : *
314 : : * SLRU buffer pool is divided in banks and bank wise SLRU lock is used as
315 : : * the control lock for the pg_notify SLRU buffers.
316 : : * In order to avoid deadlocks, whenever we need multiple locks, we first get
317 : : * NotifyQueueTailLock, then NotifyQueueLock, then SLRU bank lock, and lastly
318 : : * globalChannelTable partition locks.
319 : : *
320 : : * Each backend uses the backend[] array entry with index equal to its
321 : : * ProcNumber. We rely on this to make SendProcSignal fast.
322 : : *
323 : : * The backend[] array entries for actively-listening backends are threaded
324 : : * together using firstListener and the nextListener links, so that we can
325 : : * scan them without having to iterate over inactive entries. We keep this
326 : : * list in order by ProcNumber so that the scan is cache-friendly when there
327 : : * are many active entries.
328 : : */
329 : : typedef struct AsyncQueueControl
330 : : {
331 : : QueuePosition head; /* head points to the next free location */
332 : : QueuePosition tail; /* tail must be <= the queue position of every
333 : : * listening backend */
334 : : int64 stopPage; /* oldest unrecycled page; must be <=
335 : : * tail.page */
336 : : ProcNumber firstListener; /* id of first listener, or
337 : : * INVALID_PROC_NUMBER */
338 : : TimestampTz lastQueueFillWarn; /* time of last queue-full msg */
339 : : dsa_handle globalChannelTableDSA; /* global channel table's DSA handle */
340 : : dshash_table_handle globalChannelTableDSH; /* and its dshash handle */
341 : : /* Array with room for MaxBackends entries: */
342 : : QueueBackendStatus backend[FLEXIBLE_ARRAY_MEMBER];
343 : : } AsyncQueueControl;
344 : :
345 : : static AsyncQueueControl *asyncQueueControl;
346 : :
347 : : #define QUEUE_HEAD (asyncQueueControl->head)
348 : : #define QUEUE_TAIL (asyncQueueControl->tail)
349 : : #define QUEUE_STOP_PAGE (asyncQueueControl->stopPage)
350 : : #define QUEUE_FIRST_LISTENER (asyncQueueControl->firstListener)
351 : : #define QUEUE_BACKEND_PID(i) (asyncQueueControl->backend[i].pid)
352 : : #define QUEUE_BACKEND_DBOID(i) (asyncQueueControl->backend[i].dboid)
353 : : #define QUEUE_NEXT_LISTENER(i) (asyncQueueControl->backend[i].nextListener)
354 : : #define QUEUE_BACKEND_POS(i) (asyncQueueControl->backend[i].pos)
355 : : #define QUEUE_BACKEND_WAKEUP_PENDING(i) (asyncQueueControl->backend[i].wakeupPending)
356 : : #define QUEUE_BACKEND_IS_ADVANCING(i) (asyncQueueControl->backend[i].isAdvancing)
357 : :
358 : : /*
359 : : * The SLRU buffer area through which we access the notification queue
360 : : */
361 : : static SlruCtlData NotifyCtlData;
362 : :
363 : : #define NotifyCtl (&NotifyCtlData)
364 : : #define QUEUE_PAGESIZE BLCKSZ
365 : :
366 : : #define QUEUE_FULL_WARN_INTERVAL 5000 /* warn at most once every 5s */
367 : :
368 : : /*
369 : : * Global channel table definitions
370 : : *
371 : : * This hash table maps (database OID, channel name) keys to arrays of
372 : : * ProcNumbers representing the backends listening or about to listen
373 : : * on each channel. The "listening" flags allow us to create hash table
374 : : * entries pre-commit and not have to assume that creating them post-commit
375 : : * will succeed.
376 : : */
377 : : #define INITIAL_LISTENERS_ARRAY_SIZE 4
378 : :
379 : : typedef struct GlobalChannelKey
380 : : {
381 : : Oid dboid;
382 : : char channel[NAMEDATALEN];
383 : : } GlobalChannelKey;
384 : :
385 : : typedef struct ListenerEntry
386 : : {
387 : : ProcNumber procNo; /* listener's ProcNumber */
388 : : bool listening; /* true if committed listener */
389 : : } ListenerEntry;
390 : :
391 : : typedef struct GlobalChannelEntry
392 : : {
393 : : GlobalChannelKey key; /* hash key */
394 : : dsa_pointer listenersArray; /* DSA pointer to ListenerEntry array */
395 : : int numListeners; /* Number of listeners currently stored */
396 : : int allocatedListeners; /* Allocated size of array */
397 : : } GlobalChannelEntry;
398 : :
399 : : static dshash_table *globalChannelTable = NULL;
400 : : static dsa_area *globalChannelDSA = NULL;
401 : :
402 : : /*
403 : : * localChannelTable caches the channel names this backend is listening on
404 : : * (including those we have staged to be listened on, but not yet committed).
405 : : * Used by IsListeningOn() for fast lookups when reading notifications.
406 : : */
407 : : static HTAB *localChannelTable = NULL;
408 : :
409 : : /* We test this condition to detect that we're not listening at all */
410 : : #define LocalChannelTableIsEmpty() \
411 : : (localChannelTable == NULL || hash_get_num_entries(localChannelTable) == 0)
412 : :
413 : : /*
414 : : * State for pending LISTEN/UNLISTEN actions consists of an ordered list of
415 : : * all actions requested in the current transaction. As explained above,
416 : : * we don't actually change listen state until we reach transaction commit.
417 : : *
418 : : * The list is kept in CurTransactionContext. In subtransactions, each
419 : : * subtransaction has its own list in its own CurTransactionContext, but
420 : : * successful subtransactions attach their lists to their parent's list.
421 : : * Failed subtransactions simply discard their lists.
422 : : */
423 : : typedef enum
424 : : {
425 : : LISTEN_LISTEN,
426 : : LISTEN_UNLISTEN,
427 : : LISTEN_UNLISTEN_ALL,
428 : : } ListenActionKind;
429 : :
430 : : typedef struct
431 : : {
432 : : ListenActionKind action;
433 : : char channel[FLEXIBLE_ARRAY_MEMBER]; /* nul-terminated string */
434 : : } ListenAction;
435 : :
436 : : typedef struct ActionList
437 : : {
438 : : int nestingLevel; /* current transaction nesting depth */
439 : : List *actions; /* list of ListenAction structs */
440 : : struct ActionList *upper; /* details for upper transaction levels */
441 : : } ActionList;
442 : :
443 : : static ActionList *pendingActions = NULL;
444 : :
445 : : /*
446 : : * Hash table recording the final listen/unlisten intent per channel for
447 : : * the current transaction. Key is channel name, value is PENDING_LISTEN or
448 : : * PENDING_UNLISTEN. This keeps critical commit/abort processing to one step
449 : : * per channel instead of replaying every action. This is built from the
450 : : * pendingActions list by PreCommit_Notify, then used by AtCommit_Notify or
451 : : * AtAbort_Notify.
452 : : */
453 : : typedef enum
454 : : {
455 : : PENDING_LISTEN,
456 : : PENDING_UNLISTEN,
457 : : } PendingListenAction;
458 : :
459 : : typedef struct PendingListenEntry
460 : : {
461 : : char channel[NAMEDATALEN]; /* hash key */
462 : : PendingListenAction action; /* which action should we perform? */
463 : : } PendingListenEntry;
464 : :
465 : : static HTAB *pendingListenActions = NULL;
466 : :
467 : : /*
468 : : * State for outbound notifies consists of a list of all channels+payloads
469 : : * NOTIFYed in the current transaction. We do not actually perform a NOTIFY
470 : : * until and unless the transaction commits. pendingNotifies is NULL if no
471 : : * NOTIFYs have been done in the current (sub) transaction.
472 : : *
473 : : * We discard duplicate notify events issued in the same transaction.
474 : : * Hence, in addition to the list proper (which we need to track the order
475 : : * of the events, since we guarantee to deliver them in order), we build a
476 : : * hash table which we can probe to detect duplicates. Since building the
477 : : * hash table is somewhat expensive, we do so only once we have at least
478 : : * MIN_HASHABLE_NOTIFIES events queued in the current (sub) transaction;
479 : : * before that we just scan the events linearly.
480 : : *
481 : : * The list is kept in CurTransactionContext. In subtransactions, each
482 : : * subtransaction has its own list in its own CurTransactionContext, but
483 : : * successful subtransactions add their entries to their parent's list.
484 : : * Failed subtransactions simply discard their lists. Since these lists
485 : : * are independent, there may be notify events in a subtransaction's list
486 : : * that duplicate events in some ancestor (sub) transaction; we get rid of
487 : : * the dups when merging the subtransaction's list into its parent's.
488 : : *
489 : : * Note: the action and notify lists do not interact within a transaction.
490 : : * In particular, if a transaction does NOTIFY and then LISTEN on the same
491 : : * condition name, it will get a self-notify at commit. This is a bit odd
492 : : * but is consistent with our historical behavior.
493 : : */
494 : : typedef struct Notification
495 : : {
496 : : uint16 channel_len; /* length of channel-name string */
497 : : uint16 payload_len; /* length of payload string */
498 : : /* null-terminated channel name, then null-terminated payload follow */
499 : : char data[FLEXIBLE_ARRAY_MEMBER];
500 : : } Notification;
501 : :
502 : : typedef struct NotificationList
503 : : {
504 : : int nestingLevel; /* current transaction nesting depth */
505 : : List *events; /* list of Notification structs */
506 : : HTAB *hashtab; /* hash of NotificationHash structs, or NULL */
507 : : List *uniqueChannelNames; /* unique channel names being notified */
508 : : HTAB *uniqueChannelHash; /* hash of unique channel names, or NULL */
509 : : struct NotificationList *upper; /* details for upper transaction levels */
510 : : } NotificationList;
511 : :
512 : : #define MIN_HASHABLE_NOTIFIES 16 /* threshold to build hashtab */
513 : :
514 : : struct NotificationHash
515 : : {
516 : : Notification *event; /* => the actual Notification struct */
517 : : };
518 : :
519 : : static NotificationList *pendingNotifies = NULL;
520 : :
521 : : /*
522 : : * Hash entry in NotificationList.uniqueChannelHash or localChannelTable
523 : : * (both just carry the channel name, with no payload).
524 : : */
525 : : typedef struct ChannelName
526 : : {
527 : : char channel[NAMEDATALEN]; /* hash key */
528 : : } ChannelName;
529 : :
530 : : /*
531 : : * Inbound notifications are initially processed by HandleNotifyInterrupt(),
532 : : * called from inside a signal handler. That just sets the
533 : : * notifyInterruptPending flag and sets the process
534 : : * latch. ProcessNotifyInterrupt() will then be called whenever it's safe to
535 : : * actually deal with the interrupt.
536 : : */
537 : : volatile sig_atomic_t notifyInterruptPending = false;
538 : :
539 : : /* True if we've registered an on_shmem_exit cleanup */
540 : : static bool unlistenExitRegistered = false;
541 : :
542 : : /* True if we're currently registered as a listener in asyncQueueControl */
543 : : static bool amRegisteredListener = false;
544 : :
545 : : /*
546 : : * Queue head positions for direct advancement.
547 : : * These are captured during PreCommit_Notify while holding the heavyweight
548 : : * lock on database 0, ensuring no other backend can insert notifications
549 : : * between them. SignalBackends uses these to advance idle backends.
550 : : */
551 : : static QueuePosition queueHeadBeforeWrite;
552 : : static QueuePosition queueHeadAfterWrite;
553 : :
554 : : /*
555 : : * Workspace arrays for SignalBackends. These are preallocated in
556 : : * PreCommit_Notify to avoid needing memory allocation after committing to
557 : : * clog.
558 : : */
559 : : static int32 *signalPids = NULL;
560 : : static ProcNumber *signalProcnos = NULL;
561 : :
562 : : /* have we advanced to a page that's a multiple of QUEUE_CLEANUP_DELAY? */
563 : : static bool tryAdvanceTail = false;
564 : :
565 : : /* GUC parameters */
566 : : bool Trace_notify = false;
567 : :
568 : : /* For 8 KB pages this gives 8 GB of disk space */
569 : : int max_notify_queue_pages = 1048576;
570 : :
571 : : /* local function prototypes */
572 : : static inline int64 asyncQueuePageDiff(int64 p, int64 q);
573 : : static inline bool asyncQueuePagePrecedes(int64 p, int64 q);
574 : : static inline void GlobalChannelKeyInit(GlobalChannelKey *key, Oid dboid,
575 : : const char *channel);
576 : : static dshash_hash globalChannelTableHash(const void *key, size_t size,
577 : : void *arg);
578 : : static void initGlobalChannelTable(void);
579 : : static void initLocalChannelTable(void);
580 : : static void queue_listen(ListenActionKind action, const char *channel);
581 : : static void Async_UnlistenOnExit(int code, Datum arg);
582 : : static void BecomeRegisteredListener(void);
583 : : static void PrepareTableEntriesForListen(const char *channel);
584 : : static void PrepareTableEntriesForUnlisten(const char *channel);
585 : : static void PrepareTableEntriesForUnlistenAll(void);
586 : : static void RemoveListenerFromChannel(GlobalChannelEntry **entry_ptr,
587 : : ListenerEntry *listeners,
588 : : int idx);
589 : : static void ApplyPendingListenActions(bool isCommit);
590 : : static void CleanupListenersOnExit(void);
591 : : static bool IsListeningOn(const char *channel);
592 : : static void asyncQueueUnregister(void);
593 : : static bool asyncQueueIsFull(void);
594 : : static bool asyncQueueAdvance(volatile QueuePosition *position, int entryLength);
595 : : static void asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe);
596 : : static ListCell *asyncQueueAddEntries(ListCell *nextNotify);
597 : : static double asyncQueueUsage(void);
598 : : static void asyncQueueFillWarning(void);
599 : : static void SignalBackends(void);
600 : : static void asyncQueueReadAllNotifications(void);
601 : : static bool asyncQueueProcessPageEntries(QueuePosition *current,
602 : : QueuePosition stop,
603 : : Snapshot snapshot);
604 : : static void asyncQueueAdvanceTail(void);
605 : : static void ProcessIncomingNotify(bool flush);
606 : : static bool AsyncExistsPendingNotify(Notification *n);
607 : : static void AddEventToPendingNotifies(Notification *n);
608 : : static uint32 notification_hash(const void *key, Size keysize);
609 : : static int notification_match(const void *key1, const void *key2, Size keysize);
610 : : static void ClearPendingActionsAndNotifies(void);
611 : :
612 : : /*
613 : : * Compute the difference between two queue page numbers.
614 : : * Previously this function accounted for a wraparound.
615 : : */
616 : : static inline int64
617 : 0 : asyncQueuePageDiff(int64 p, int64 q)
618 : : {
619 : 0 : return p - q;
620 : : }
621 : :
622 : : /*
623 : : * Determines whether p precedes q.
624 : : * Previously this function accounted for a wraparound.
625 : : */
626 : : static inline bool
627 : 1 : asyncQueuePagePrecedes(int64 p, int64 q)
628 : : {
629 : 1 : return p < q;
630 : : }
631 : :
632 : : /*
633 : : * GlobalChannelKeyInit
634 : : * Prepare a global channel table key for hashing.
635 : : */
636 : : static inline void
637 : 10 : GlobalChannelKeyInit(GlobalChannelKey *key, Oid dboid, const char *channel)
638 : : {
639 : 10 : memset(key, 0, sizeof(GlobalChannelKey));
640 : 10 : key->dboid = dboid;
641 : 10 : strlcpy(key->channel, channel, NAMEDATALEN);
642 : 10 : }
643 : :
644 : : /*
645 : : * globalChannelTableHash
646 : : * Hash function for global channel table keys.
647 : : */
648 : : static dshash_hash
649 : 10 : globalChannelTableHash(const void *key, size_t size, void *arg)
650 : : {
651 : 10 : const GlobalChannelKey *k = (const GlobalChannelKey *) key;
652 : 10 : dshash_hash h;
653 : :
654 : 10 : h = DatumGetUInt32(hash_uint32(k->dboid));
655 : 20 : h ^= DatumGetUInt32(hash_any((const unsigned char *) k->channel,
656 : 10 : strnlen(k->channel, NAMEDATALEN)));
657 : :
658 : 20 : return h;
659 : 10 : }
660 : :
661 : : /* parameters for the global channel table */
662 : : static const dshash_parameters globalChannelTableDSHParams = {
663 : : sizeof(GlobalChannelKey),
664 : : sizeof(GlobalChannelEntry),
665 : : dshash_memcmp,
666 : : globalChannelTableHash,
667 : : dshash_memcpy,
668 : : LWTRANCHE_NOTIFY_CHANNEL_HASH
669 : : };
670 : :
671 : : /*
672 : : * initGlobalChannelTable
673 : : * Lazy initialization of the global channel table.
674 : : */
675 : : static void
676 : 9 : initGlobalChannelTable(void)
677 : : {
678 : 9 : MemoryContext oldcontext;
679 : :
680 : : /* Quick exit if we already did this */
681 [ + + + + ]: 9 : if (asyncQueueControl->globalChannelTableDSH != DSHASH_HANDLE_INVALID &&
682 : 8 : globalChannelTable != NULL)
683 : 7 : return;
684 : :
685 : : /* Otherwise, use a lock to ensure only one process creates the table */
686 : 2 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
687 : :
688 : : /* Be sure any local memory allocated by DSA routines is persistent */
689 : 2 : oldcontext = MemoryContextSwitchTo(TopMemoryContext);
690 : :
691 [ + + ]: 2 : if (asyncQueueControl->globalChannelTableDSH == DSHASH_HANDLE_INVALID)
692 : : {
693 : : /* Initialize dynamic shared hash table for global channels */
694 : 1 : globalChannelDSA = dsa_create(LWTRANCHE_NOTIFY_CHANNEL_HASH);
695 : 1 : dsa_pin(globalChannelDSA);
696 : 1 : dsa_pin_mapping(globalChannelDSA);
697 : 1 : globalChannelTable = dshash_create(globalChannelDSA,
698 : : &globalChannelTableDSHParams,
699 : : NULL);
700 : :
701 : : /* Store handles in shared memory for other backends to use */
702 : 1 : asyncQueueControl->globalChannelTableDSA = dsa_get_handle(globalChannelDSA);
703 : 1 : asyncQueueControl->globalChannelTableDSH =
704 : 1 : dshash_get_hash_table_handle(globalChannelTable);
705 : 1 : }
706 [ - + ]: 1 : else if (!globalChannelTable)
707 : : {
708 : : /* Attach to existing dynamic shared hash table */
709 : 1 : globalChannelDSA = dsa_attach(asyncQueueControl->globalChannelTableDSA);
710 : 1 : dsa_pin_mapping(globalChannelDSA);
711 : 2 : globalChannelTable = dshash_attach(globalChannelDSA,
712 : : &globalChannelTableDSHParams,
713 : 1 : asyncQueueControl->globalChannelTableDSH,
714 : : NULL);
715 : 1 : }
716 : :
717 : 2 : MemoryContextSwitchTo(oldcontext);
718 : 2 : LWLockRelease(NotifyQueueLock);
719 [ - + ]: 9 : }
720 : :
721 : : /*
722 : : * initLocalChannelTable
723 : : * Lazy initialization of the local channel table.
724 : : * Once created, this table lasts for the life of the session.
725 : : */
726 : : static void
727 : 5 : initLocalChannelTable(void)
728 : : {
729 : 5 : HASHCTL hash_ctl;
730 : :
731 : : /* Quick exit if we already did this */
732 [ + + ]: 5 : if (localChannelTable != NULL)
733 : 3 : return;
734 : :
735 : : /* Initialize local hash table for this backend's listened channels */
736 : 2 : hash_ctl.keysize = NAMEDATALEN;
737 : 2 : hash_ctl.entrysize = sizeof(ChannelName);
738 : :
739 : 2 : localChannelTable =
740 : 2 : hash_create("Local Listen Channels",
741 : : 64,
742 : : &hash_ctl,
743 : : HASH_ELEM | HASH_STRINGS);
744 [ - + ]: 5 : }
745 : :
746 : : /*
747 : : * initPendingListenActions
748 : : * Lazy initialization of the pending listen actions hash table.
749 : : * This is allocated in CurTransactionContext during PreCommit_Notify,
750 : : * and destroyed at transaction end.
751 : : */
752 : : static void
753 : 5 : initPendingListenActions(void)
754 : : {
755 : 5 : HASHCTL hash_ctl;
756 : :
757 [ - + ]: 5 : if (pendingListenActions != NULL)
758 : 0 : return;
759 : :
760 : 5 : hash_ctl.keysize = NAMEDATALEN;
761 : 5 : hash_ctl.entrysize = sizeof(PendingListenEntry);
762 : 5 : hash_ctl.hcxt = CurTransactionContext;
763 : :
764 : 5 : pendingListenActions =
765 : 5 : hash_create("Pending Listen Actions",
766 : 5 : list_length(pendingActions->actions),
767 : : &hash_ctl,
768 : : HASH_ELEM | HASH_STRINGS | HASH_CONTEXT);
769 [ - + ]: 5 : }
770 : :
771 : : /*
772 : : * Report space needed for our shared memory area
773 : : */
774 : : Size
775 : 9 : AsyncShmemSize(void)
776 : : {
777 : 9 : Size size;
778 : :
779 : : /* This had better match AsyncShmemInit */
780 : 9 : size = mul_size(MaxBackends, sizeof(QueueBackendStatus));
781 : 9 : size = add_size(size, offsetof(AsyncQueueControl, backend));
782 : :
783 : 9 : size = add_size(size, SimpleLruShmemSize(notify_buffers, 0));
784 : :
785 : 18 : return size;
786 : 9 : }
787 : :
788 : : /*
789 : : * Initialize our shared memory area
790 : : */
791 : : void
792 : 6 : AsyncShmemInit(void)
793 : : {
794 : 6 : bool found;
795 : 6 : Size size;
796 : :
797 : : /*
798 : : * Create or attach to the AsyncQueueControl structure.
799 : : */
800 : 6 : size = mul_size(MaxBackends, sizeof(QueueBackendStatus));
801 : 6 : size = add_size(size, offsetof(AsyncQueueControl, backend));
802 : :
803 : 6 : asyncQueueControl = (AsyncQueueControl *)
804 : 6 : ShmemInitStruct("Async Queue Control", size, &found);
805 : :
806 [ - + ]: 6 : if (!found)
807 : : {
808 : : /* First time through, so initialize it */
809 : 6 : SET_QUEUE_POS(QUEUE_HEAD, 0, 0);
810 : 6 : SET_QUEUE_POS(QUEUE_TAIL, 0, 0);
811 : 6 : QUEUE_STOP_PAGE = 0;
812 : 6 : QUEUE_FIRST_LISTENER = INVALID_PROC_NUMBER;
813 : 6 : asyncQueueControl->lastQueueFillWarn = 0;
814 : 6 : asyncQueueControl->globalChannelTableDSA = DSA_HANDLE_INVALID;
815 : 6 : asyncQueueControl->globalChannelTableDSH = DSHASH_HANDLE_INVALID;
816 [ + + ]: 812 : for (int i = 0; i < MaxBackends; i++)
817 : : {
818 : 806 : QUEUE_BACKEND_PID(i) = InvalidPid;
819 : 806 : QUEUE_BACKEND_DBOID(i) = InvalidOid;
820 : 806 : QUEUE_NEXT_LISTENER(i) = INVALID_PROC_NUMBER;
821 : 806 : SET_QUEUE_POS(QUEUE_BACKEND_POS(i), 0, 0);
822 : 806 : QUEUE_BACKEND_WAKEUP_PENDING(i) = false;
823 : 806 : QUEUE_BACKEND_IS_ADVANCING(i) = false;
824 : 806 : }
825 : 6 : }
826 : :
827 : : /*
828 : : * Set up SLRU management of the pg_notify data. Note that long segment
829 : : * names are used in order to avoid wraparound.
830 : : */
831 : 6 : NotifyCtl->PagePrecedes = asyncQueuePagePrecedes;
832 : 6 : SimpleLruInit(NotifyCtl, "notify", notify_buffers, 0,
833 : : "pg_notify", LWTRANCHE_NOTIFY_BUFFER, LWTRANCHE_NOTIFY_SLRU,
834 : : SYNC_HANDLER_NONE, true);
835 : :
836 [ - + ]: 6 : if (!found)
837 : : {
838 : : /*
839 : : * During start or reboot, clean out the pg_notify directory.
840 : : */
841 : 6 : (void) SlruScanDirectory(NotifyCtl, SlruScanDirCbDeleteAll, NULL);
842 : 6 : }
843 : 6 : }
844 : :
845 : :
846 : : /*
847 : : * pg_notify -
848 : : * SQL function to send a notification event
849 : : */
850 : : Datum
851 : 6 : pg_notify(PG_FUNCTION_ARGS)
852 : : {
853 : 6 : const char *channel;
854 : 6 : const char *payload;
855 : :
856 [ + + ]: 6 : if (PG_ARGISNULL(0))
857 : 1 : channel = "";
858 : : else
859 : 5 : channel = text_to_cstring(PG_GETARG_TEXT_PP(0));
860 : :
861 [ + + ]: 6 : if (PG_ARGISNULL(1))
862 : 1 : payload = "";
863 : : else
864 : 5 : payload = text_to_cstring(PG_GETARG_TEXT_PP(1));
865 : :
866 : : /* For NOTIFY as a statement, this is checked in ProcessUtility */
867 : 6 : PreventCommandDuringRecovery("NOTIFY");
868 : :
869 : 6 : Async_Notify(channel, payload);
870 : :
871 : 6 : PG_RETURN_VOID();
872 : 6 : }
873 : :
874 : :
875 : : /*
876 : : * Async_Notify
877 : : *
878 : : * This is executed by the SQL notify command.
879 : : *
880 : : * Adds the message to the list of pending notifies.
881 : : * Actual notification happens during transaction commit.
882 : : * ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
883 : : */
884 : : void
885 : 7 : Async_Notify(const char *channel, const char *payload)
886 : : {
887 : 7 : int my_level = GetCurrentTransactionNestLevel();
888 : 7 : size_t channel_len;
889 : 7 : size_t payload_len;
890 : 7 : Notification *n;
891 : 7 : MemoryContext oldcontext;
892 : :
893 [ + - ]: 7 : if (IsParallelWorker())
894 [ # # # # ]: 0 : elog(ERROR, "cannot send notifications from a parallel worker");
895 : :
896 [ + - ]: 7 : if (Trace_notify)
897 [ # # # # ]: 0 : elog(DEBUG1, "Async_Notify(%s)", channel);
898 : :
899 [ + - ]: 7 : channel_len = channel ? strlen(channel) : 0;
900 [ + + ]: 7 : payload_len = payload ? strlen(payload) : 0;
901 : :
902 : : /* a channel name must be specified */
903 [ + + ]: 7 : if (channel_len == 0)
904 [ + - + - ]: 2 : ereport(ERROR,
905 : : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
906 : : errmsg("channel name cannot be empty")));
907 : :
908 : : /* enforce length limits */
909 [ + + ]: 5 : if (channel_len >= NAMEDATALEN)
910 [ + - + - ]: 1 : ereport(ERROR,
911 : : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
912 : : errmsg("channel name too long")));
913 : :
914 [ + - ]: 4 : if (payload_len >= NOTIFY_PAYLOAD_MAX_LENGTH)
915 [ # # # # ]: 0 : ereport(ERROR,
916 : : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
917 : : errmsg("payload string too long")));
918 : :
919 : : /*
920 : : * We must construct the Notification entry, even if we end up not using
921 : : * it, in order to compare it cheaply to existing list entries.
922 : : *
923 : : * The notification list needs to live until end of transaction, so store
924 : : * it in the transaction context.
925 : : */
926 : 4 : oldcontext = MemoryContextSwitchTo(CurTransactionContext);
927 : :
928 : 8 : n = (Notification *) palloc(offsetof(Notification, data) +
929 : 8 : channel_len + payload_len + 2);
930 : 4 : n->channel_len = channel_len;
931 : 4 : n->payload_len = payload_len;
932 : 4 : strcpy(n->data, channel);
933 [ + + ]: 4 : if (payload)
934 : 3 : strcpy(n->data + channel_len + 1, payload);
935 : : else
936 : 1 : n->data[channel_len + 1] = '\0';
937 : :
938 [ - + # # ]: 4 : if (pendingNotifies == NULL || my_level > pendingNotifies->nestingLevel)
939 : : {
940 : 4 : NotificationList *notifies;
941 : :
942 : : /*
943 : : * First notify event in current (sub)xact. Note that we allocate the
944 : : * NotificationList in TopTransactionContext; the nestingLevel might
945 : : * get changed later by AtSubCommit_Notify.
946 : : */
947 : 4 : notifies = (NotificationList *)
948 : 4 : MemoryContextAlloc(TopTransactionContext,
949 : : sizeof(NotificationList));
950 : 4 : notifies->nestingLevel = my_level;
951 : 4 : notifies->events = list_make1(n);
952 : : /* We certainly don't need a hashtable yet */
953 : 4 : notifies->hashtab = NULL;
954 : : /* We won't build uniqueChannelNames/Hash till later, either */
955 : 4 : notifies->uniqueChannelNames = NIL;
956 : 4 : notifies->uniqueChannelHash = NULL;
957 : 4 : notifies->upper = pendingNotifies;
958 : 4 : pendingNotifies = notifies;
959 : 4 : }
960 : : else
961 : : {
962 : : /* Now check for duplicates */
963 [ # # ]: 0 : if (AsyncExistsPendingNotify(n))
964 : : {
965 : : /* It's a dup, so forget it */
966 : 0 : pfree(n);
967 : 0 : MemoryContextSwitchTo(oldcontext);
968 : 0 : return;
969 : : }
970 : :
971 : : /* Append more events to existing list */
972 : 0 : AddEventToPendingNotifies(n);
973 : : }
974 : :
975 : 4 : MemoryContextSwitchTo(oldcontext);
976 [ - + ]: 4 : }
977 : :
978 : : /*
979 : : * queue_listen
980 : : * Common code for listen, unlisten, unlisten all commands.
981 : : *
982 : : * Adds the request to the list of pending actions.
983 : : * Actual update of localChannelTable and globalChannelTable happens during
984 : : * PreCommit_Notify, with staged changes committed in AtCommit_Notify.
985 : : */
986 : : static void
987 : 5 : queue_listen(ListenActionKind action, const char *channel)
988 : : {
989 : 5 : MemoryContext oldcontext;
990 : 5 : ListenAction *actrec;
991 : 5 : int my_level = GetCurrentTransactionNestLevel();
992 : :
993 : : /*
994 : : * Unlike Async_Notify, we don't try to collapse out duplicates here. We
995 : : * keep the ordered list to preserve interactions like UNLISTEN ALL; the
996 : : * final per-channel intent is computed during PreCommit_Notify.
997 : : */
998 : 5 : oldcontext = MemoryContextSwitchTo(CurTransactionContext);
999 : :
1000 : : /* space for terminating null is included in sizeof(ListenAction) */
1001 : 10 : actrec = (ListenAction *) palloc(offsetof(ListenAction, channel) +
1002 : 10 : strlen(channel) + 1);
1003 : 5 : actrec->action = action;
1004 : 5 : strcpy(actrec->channel, channel);
1005 : :
1006 [ - + # # ]: 5 : if (pendingActions == NULL || my_level > pendingActions->nestingLevel)
1007 : : {
1008 : 5 : ActionList *actions;
1009 : :
1010 : : /*
1011 : : * First action in current sub(xact). Note that we allocate the
1012 : : * ActionList in TopTransactionContext; the nestingLevel might get
1013 : : * changed later by AtSubCommit_Notify.
1014 : : */
1015 : 5 : actions = (ActionList *)
1016 : 5 : MemoryContextAlloc(TopTransactionContext, sizeof(ActionList));
1017 : 5 : actions->nestingLevel = my_level;
1018 : 5 : actions->actions = list_make1(actrec);
1019 : 5 : actions->upper = pendingActions;
1020 : 5 : pendingActions = actions;
1021 : 5 : }
1022 : : else
1023 : 0 : pendingActions->actions = lappend(pendingActions->actions, actrec);
1024 : :
1025 : 5 : MemoryContextSwitchTo(oldcontext);
1026 : 5 : }
1027 : :
1028 : : /*
1029 : : * Async_Listen
1030 : : *
1031 : : * This is executed by the SQL listen command.
1032 : : */
1033 : : void
1034 : 2 : Async_Listen(const char *channel)
1035 : : {
1036 [ + - ]: 2 : if (Trace_notify)
1037 [ # # # # ]: 0 : elog(DEBUG1, "Async_Listen(%s,%d)", channel, MyProcPid);
1038 : :
1039 : 2 : queue_listen(LISTEN_LISTEN, channel);
1040 : 2 : }
1041 : :
1042 : : /*
1043 : : * Async_Unlisten
1044 : : *
1045 : : * This is executed by the SQL unlisten command.
1046 : : */
1047 : : void
1048 : 1 : Async_Unlisten(const char *channel)
1049 : : {
1050 [ + - ]: 1 : if (Trace_notify)
1051 [ # # # # ]: 0 : elog(DEBUG1, "Async_Unlisten(%s,%d)", channel, MyProcPid);
1052 : :
1053 : : /* If we couldn't possibly be listening, no need to queue anything */
1054 [ + - + - ]: 1 : if (pendingActions == NULL && !unlistenExitRegistered)
1055 : 0 : return;
1056 : :
1057 : 1 : queue_listen(LISTEN_UNLISTEN, channel);
1058 : 1 : }
1059 : :
1060 : : /*
1061 : : * Async_UnlistenAll
1062 : : *
1063 : : * This is invoked by UNLISTEN * command, and also at backend exit.
1064 : : */
1065 : : void
1066 : 2 : Async_UnlistenAll(void)
1067 : : {
1068 [ + - ]: 2 : if (Trace_notify)
1069 [ # # # # ]: 0 : elog(DEBUG1, "Async_UnlistenAll(%d)", MyProcPid);
1070 : :
1071 : : /* If we couldn't possibly be listening, no need to queue anything */
1072 [ + - + - ]: 2 : if (pendingActions == NULL && !unlistenExitRegistered)
1073 : 0 : return;
1074 : :
1075 : 2 : queue_listen(LISTEN_UNLISTEN_ALL, "");
1076 : 2 : }
1077 : :
1078 : : /*
1079 : : * SQL function: return a set of the channel names this backend is actively
1080 : : * listening to.
1081 : : *
1082 : : * Note: this coding relies on the fact that the localChannelTable cannot
1083 : : * change within a transaction.
1084 : : */
1085 : : Datum
1086 : 3 : pg_listening_channels(PG_FUNCTION_ARGS)
1087 : : {
1088 : 3 : FuncCallContext *funcctx;
1089 : 3 : HASH_SEQ_STATUS *status;
1090 : :
1091 : : /* stuff done only on the first call of the function */
1092 [ + + ]: 3 : if (SRF_IS_FIRSTCALL())
1093 : : {
1094 : : /* create a function context for cross-call persistence */
1095 : 2 : funcctx = SRF_FIRSTCALL_INIT();
1096 : :
1097 : : /* Initialize hash table iteration if we have any channels */
1098 [ + - ]: 2 : if (localChannelTable != NULL)
1099 : : {
1100 : 2 : MemoryContext oldcontext;
1101 : :
1102 : 2 : oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);
1103 : 2 : status = (HASH_SEQ_STATUS *) palloc(sizeof(HASH_SEQ_STATUS));
1104 : 2 : hash_seq_init(status, localChannelTable);
1105 : 2 : funcctx->user_fctx = status;
1106 : 2 : MemoryContextSwitchTo(oldcontext);
1107 : 2 : }
1108 : : else
1109 : : {
1110 : 0 : funcctx->user_fctx = NULL;
1111 : : }
1112 : 2 : }
1113 : :
1114 : : /* stuff done on every call of the function */
1115 : 3 : funcctx = SRF_PERCALL_SETUP();
1116 : 3 : status = (HASH_SEQ_STATUS *) funcctx->user_fctx;
1117 : :
1118 [ - + ]: 3 : if (status != NULL)
1119 : : {
1120 : 3 : ChannelName *entry;
1121 : :
1122 : 3 : entry = (ChannelName *) hash_seq_search(status);
1123 [ + + ]: 3 : if (entry != NULL)
1124 : 1 : SRF_RETURN_NEXT(funcctx, CStringGetTextDatum(entry->channel));
1125 [ + + ]: 3 : }
1126 : :
1127 [ + - ]: 2 : SRF_RETURN_DONE(funcctx);
1128 [ - + ]: 3 : }
1129 : :
1130 : : /*
1131 : : * Async_UnlistenOnExit
1132 : : *
1133 : : * This is executed at backend exit if we have done any LISTENs in this
1134 : : * backend. It might not be necessary anymore, if the user UNLISTENed
1135 : : * everything, but we don't try to detect that case.
1136 : : */
1137 : : static void
1138 : 2 : Async_UnlistenOnExit(int code, Datum arg)
1139 : : {
1140 : 2 : CleanupListenersOnExit();
1141 : 2 : asyncQueueUnregister();
1142 : 2 : }
1143 : :
1144 : : /*
1145 : : * AtPrepare_Notify
1146 : : *
1147 : : * This is called at the prepare phase of a two-phase
1148 : : * transaction. Save the state for possible commit later.
1149 : : */
1150 : : void
1151 : 0 : AtPrepare_Notify(void)
1152 : : {
1153 : : /* It's not allowed to have any pending LISTEN/UNLISTEN/NOTIFY actions */
1154 [ # # ]: 0 : if (pendingActions || pendingNotifies)
1155 [ # # # # ]: 0 : ereport(ERROR,
1156 : : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
1157 : : errmsg("cannot PREPARE a transaction that has executed LISTEN, UNLISTEN, or NOTIFY")));
1158 : 0 : }
1159 : :
1160 : : /*
1161 : : * PreCommit_Notify
1162 : : *
1163 : : * This is called at transaction commit, before actually committing to
1164 : : * clog.
1165 : : *
1166 : : * If there are pending LISTEN actions, make sure we are listed in the
1167 : : * shared-memory listener array. This must happen before commit to
1168 : : * ensure we don't miss any notifies from transactions that commit
1169 : : * just after ours.
1170 : : *
1171 : : * If there are outbound notify requests in the pendingNotifies list,
1172 : : * add them to the global queue. We do that before commit so that
1173 : : * we can still throw error if we run out of queue space.
1174 : : */
1175 : : void
1176 : 50901 : PreCommit_Notify(void)
1177 : : {
1178 : 50901 : ListCell *p;
1179 : :
1180 [ + + + + ]: 50901 : if (!pendingActions && !pendingNotifies)
1181 : 50892 : return; /* no relevant statements in this xact */
1182 : :
1183 [ + - ]: 9 : if (Trace_notify)
1184 [ # # # # ]: 0 : elog(DEBUG1, "PreCommit_Notify");
1185 : :
1186 : : /* Preflight for any pending listen/unlisten actions */
1187 : 9 : initGlobalChannelTable();
1188 : :
1189 [ + + ]: 9 : if (pendingActions != NULL)
1190 : : {
1191 : : /* Ensure we have a local channel table */
1192 : 5 : initLocalChannelTable();
1193 : : /* Create pendingListenActions hash table for this transaction */
1194 : 5 : initPendingListenActions();
1195 : :
1196 : : /* Stage all the actions this transaction wants to perform */
1197 [ + - + + : 10 : foreach(p, pendingActions->actions)
+ + ]
1198 : : {
1199 : 5 : ListenAction *actrec = (ListenAction *) lfirst(p);
1200 : :
1201 [ + - + + ]: 5 : switch (actrec->action)
1202 : : {
1203 : : case LISTEN_LISTEN:
1204 : 2 : BecomeRegisteredListener();
1205 : 2 : PrepareTableEntriesForListen(actrec->channel);
1206 : 2 : break;
1207 : : case LISTEN_UNLISTEN:
1208 : 1 : PrepareTableEntriesForUnlisten(actrec->channel);
1209 : 1 : break;
1210 : : case LISTEN_UNLISTEN_ALL:
1211 : 2 : PrepareTableEntriesForUnlistenAll();
1212 : 2 : break;
1213 : : }
1214 : 5 : }
1215 : 5 : }
1216 : :
1217 : : /* Queue any pending notifies (must happen after the above) */
1218 [ + + ]: 9 : if (pendingNotifies)
1219 : : {
1220 : 4 : ListCell *nextNotify;
1221 : 4 : bool firstIteration = true;
1222 : :
1223 : : /*
1224 : : * Build list of unique channel names being notified for use by
1225 : : * SignalBackends().
1226 : : *
1227 : : * If uniqueChannelHash is available, use it to efficiently get the
1228 : : * unique channels. Otherwise, fall back to the O(N^2) approach.
1229 : : */
1230 : 4 : pendingNotifies->uniqueChannelNames = NIL;
1231 [ - + ]: 4 : if (pendingNotifies->uniqueChannelHash != NULL)
1232 : : {
1233 : 0 : HASH_SEQ_STATUS status;
1234 : 0 : ChannelName *channelEntry;
1235 : :
1236 : 0 : hash_seq_init(&status, pendingNotifies->uniqueChannelHash);
1237 [ # # ]: 0 : while ((channelEntry = (ChannelName *) hash_seq_search(&status)) != NULL)
1238 : 0 : pendingNotifies->uniqueChannelNames =
1239 : 0 : lappend(pendingNotifies->uniqueChannelNames,
1240 : 0 : channelEntry->channel);
1241 : 0 : }
1242 : : else
1243 : : {
1244 : : /* O(N^2) approach is better for small number of notifications */
1245 [ + + + - : 12 : foreach_ptr(Notification, n, pendingNotifies->events)
+ + + + ]
1246 : : {
1247 : 4 : char *channel = n->data;
1248 : 4 : bool found = false;
1249 : :
1250 : : /* Name present in list? */
1251 [ + + - + : 8 : foreach_ptr(char, oldchan, pendingNotifies->uniqueChannelNames)
# # - + ]
1252 : : {
1253 [ # # ]: 0 : if (strcmp(oldchan, channel) == 0)
1254 : : {
1255 : 0 : found = true;
1256 : 0 : break;
1257 : : }
1258 : 4 : }
1259 : : /* Add if not already in list */
1260 [ - + ]: 4 : if (!found)
1261 : 4 : pendingNotifies->uniqueChannelNames =
1262 : 8 : lappend(pendingNotifies->uniqueChannelNames,
1263 : 4 : channel);
1264 : 8 : }
1265 : : }
1266 : :
1267 : : /* Preallocate workspace that will be needed by SignalBackends() */
1268 [ + + ]: 4 : if (signalPids == NULL)
1269 : 2 : signalPids = MemoryContextAlloc(TopMemoryContext,
1270 : 1 : MaxBackends * sizeof(int32));
1271 : :
1272 [ + + ]: 4 : if (signalProcnos == NULL)
1273 : 2 : signalProcnos = MemoryContextAlloc(TopMemoryContext,
1274 : 1 : MaxBackends * sizeof(ProcNumber));
1275 : :
1276 : : /*
1277 : : * Make sure that we have an XID assigned to the current transaction.
1278 : : * GetCurrentTransactionId is cheap if we already have an XID, but not
1279 : : * so cheap if we don't, and we'd prefer not to do that work while
1280 : : * holding NotifyQueueLock.
1281 : : */
1282 : 4 : (void) GetCurrentTransactionId();
1283 : :
1284 : : /*
1285 : : * Serialize writers by acquiring a special lock that we hold till
1286 : : * after commit. This ensures that queue entries appear in commit
1287 : : * order, and in particular that there are never uncommitted queue
1288 : : * entries ahead of committed ones, so an uncommitted transaction
1289 : : * can't block delivery of deliverable notifications.
1290 : : *
1291 : : * We use a heavyweight lock so that it'll automatically be released
1292 : : * after either commit or abort. This also allows deadlocks to be
1293 : : * detected, though really a deadlock shouldn't be possible here.
1294 : : *
1295 : : * The lock is on "database 0", which is pretty ugly but it doesn't
1296 : : * seem worth inventing a special locktag category just for this.
1297 : : * (Historical note: before PG 9.0, a similar lock on "database 0" was
1298 : : * used by the flatfiles mechanism.)
1299 : : */
1300 : 4 : LockSharedObject(DatabaseRelationId, InvalidOid, 0,
1301 : : AccessExclusiveLock);
1302 : :
1303 : : /*
1304 : : * For the direct advancement optimization in SignalBackends(), we
1305 : : * need to ensure that no other backend can insert queue entries
1306 : : * between queueHeadBeforeWrite and queueHeadAfterWrite. The
1307 : : * heavyweight lock above provides this guarantee, since it serializes
1308 : : * all writers.
1309 : : *
1310 : : * Note: if the heavyweight lock were ever removed for scalability
1311 : : * reasons, we could achieve the same guarantee by holding
1312 : : * NotifyQueueLock in EXCLUSIVE mode across all our insertions, rather
1313 : : * than releasing and reacquiring it for each page as we do below.
1314 : : */
1315 : :
1316 : : /* Initialize values to a safe default in case list is empty */
1317 : 4 : SET_QUEUE_POS(queueHeadBeforeWrite, 0, 0);
1318 : 4 : SET_QUEUE_POS(queueHeadAfterWrite, 0, 0);
1319 : :
1320 : : /* Now push the notifications into the queue */
1321 : 4 : nextNotify = list_head(pendingNotifies->events);
1322 [ + + ]: 8 : while (nextNotify != NULL)
1323 : : {
1324 : : /*
1325 : : * Add the pending notifications to the queue. We acquire and
1326 : : * release NotifyQueueLock once per page, which might be overkill
1327 : : * but it does allow readers to get in while we're doing this.
1328 : : *
1329 : : * A full queue is very uncommon and should really not happen,
1330 : : * given that we have so much space available in the SLRU pages.
1331 : : * Nevertheless we need to deal with this possibility. Note that
1332 : : * when we get here we are in the process of committing our
1333 : : * transaction, but we have not yet committed to clog, so at this
1334 : : * point in time we can still roll the transaction back.
1335 : : */
1336 : 4 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
1337 [ - + ]: 4 : if (firstIteration)
1338 : : {
1339 : 4 : queueHeadBeforeWrite = QUEUE_HEAD;
1340 : 4 : firstIteration = false;
1341 : 4 : }
1342 : 4 : asyncQueueFillWarning();
1343 [ + - ]: 4 : if (asyncQueueIsFull())
1344 [ # # # # ]: 0 : ereport(ERROR,
1345 : : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
1346 : : errmsg("too many notifications in the NOTIFY queue")));
1347 : 4 : nextNotify = asyncQueueAddEntries(nextNotify);
1348 : 4 : queueHeadAfterWrite = QUEUE_HEAD;
1349 : 4 : LWLockRelease(NotifyQueueLock);
1350 : : }
1351 : :
1352 : : /* Note that we don't clear pendingNotifies; AtCommit_Notify will. */
1353 : 4 : }
1354 [ - + ]: 50901 : }
1355 : :
1356 : : /*
1357 : : * AtCommit_Notify
1358 : : *
1359 : : * This is called at transaction commit, after committing to clog.
1360 : : *
1361 : : * Apply pending listen/unlisten changes and clear transaction-local state.
1362 : : *
1363 : : * If we issued any notifications in the transaction, send signals to
1364 : : * listening backends (possibly including ourselves) to process them.
1365 : : * Also, if we filled enough queue pages with new notifies, try to
1366 : : * advance the queue tail pointer.
1367 : : */
1368 : : void
1369 : 50901 : AtCommit_Notify(void)
1370 : : {
1371 : : /*
1372 : : * Allow transactions that have not executed LISTEN/UNLISTEN/NOTIFY to
1373 : : * return as soon as possible
1374 : : */
1375 [ + + + + ]: 50901 : if (!pendingActions && !pendingNotifies)
1376 : 50892 : return;
1377 : :
1378 [ + - ]: 9 : if (Trace_notify)
1379 [ # # # # ]: 0 : elog(DEBUG1, "AtCommit_Notify");
1380 : :
1381 : : /* Apply staged listen/unlisten changes */
1382 : 9 : ApplyPendingListenActions(true);
1383 : :
1384 : : /* If no longer listening to anything, get out of listener array */
1385 [ + + + - : 9 : if (amRegisteredListener && LocalChannelTableIsEmpty())
+ + ]
1386 : 2 : asyncQueueUnregister();
1387 : :
1388 : : /*
1389 : : * Send signals to listening backends. We need do this only if there are
1390 : : * pending notifies, which were previously added to the shared queue by
1391 : : * PreCommit_Notify().
1392 : : */
1393 [ + + ]: 9 : if (pendingNotifies != NULL)
1394 : 4 : SignalBackends();
1395 : :
1396 : : /*
1397 : : * If it's time to try to advance the global tail pointer, do that.
1398 : : *
1399 : : * (It might seem odd to do this in the sender, when more than likely the
1400 : : * listeners won't yet have read the messages we just sent. However,
1401 : : * there's less contention if only the sender does it, and there is little
1402 : : * need for urgency in advancing the global tail. So this typically will
1403 : : * be clearing out messages that were sent some time ago.)
1404 : : */
1405 [ + - ]: 9 : if (tryAdvanceTail)
1406 : : {
1407 : 0 : tryAdvanceTail = false;
1408 : 0 : asyncQueueAdvanceTail();
1409 : 0 : }
1410 : :
1411 : : /* And clean up */
1412 : 9 : ClearPendingActionsAndNotifies();
1413 : 50901 : }
1414 : :
1415 : : /*
1416 : : * BecomeRegisteredListener --- subroutine for PreCommit_Notify
1417 : : *
1418 : : * This function must make sure we are ready to catch any incoming messages.
1419 : : */
1420 : : static void
1421 : 2 : BecomeRegisteredListener(void)
1422 : : {
1423 : 2 : QueuePosition head;
1424 : 2 : QueuePosition max;
1425 : 2 : ProcNumber prevListener;
1426 : :
1427 : : /*
1428 : : * Nothing to do if we are already listening to something, nor if we
1429 : : * already ran this routine in this transaction.
1430 : : */
1431 [ - + ]: 2 : if (amRegisteredListener)
1432 : 0 : return;
1433 : :
1434 [ + - ]: 2 : if (Trace_notify)
1435 [ # # # # ]: 0 : elog(DEBUG1, "BecomeRegisteredListener(%d)", MyProcPid);
1436 : :
1437 : : /*
1438 : : * Before registering, make sure we will unlisten before dying. (Note:
1439 : : * this action does not get undone if we abort later.)
1440 : : */
1441 [ - + ]: 2 : if (!unlistenExitRegistered)
1442 : : {
1443 : 2 : before_shmem_exit(Async_UnlistenOnExit, 0);
1444 : 2 : unlistenExitRegistered = true;
1445 : 2 : }
1446 : :
1447 : : /*
1448 : : * This is our first LISTEN, so establish our pointer.
1449 : : *
1450 : : * We set our pointer to the global tail pointer and then move it forward
1451 : : * over already-committed notifications. This ensures we cannot miss any
1452 : : * not-yet-committed notifications. We might get a few more but that
1453 : : * doesn't hurt.
1454 : : *
1455 : : * In some scenarios there might be a lot of committed notifications that
1456 : : * have not yet been pruned away (because some backend is being lazy about
1457 : : * reading them). To reduce our startup time, we can look at other
1458 : : * backends and adopt the maximum "pos" pointer of any backend that's in
1459 : : * our database; any notifications it's already advanced over are surely
1460 : : * committed and need not be re-examined by us. (We must consider only
1461 : : * backends connected to our DB, because others will not have bothered to
1462 : : * check committed-ness of notifications in our DB.)
1463 : : *
1464 : : * We need exclusive lock here so we can look at other backends' entries
1465 : : * and manipulate the list links.
1466 : : */
1467 : 2 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
1468 : 2 : head = QUEUE_HEAD;
1469 : 2 : max = QUEUE_TAIL;
1470 : 2 : prevListener = INVALID_PROC_NUMBER;
1471 [ - + ]: 2 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1472 : : {
1473 [ # # ]: 0 : if (QUEUE_BACKEND_DBOID(i) == MyDatabaseId)
1474 [ # # # # : 0 : max = QUEUE_POS_MAX(max, QUEUE_BACKEND_POS(i));
# # ]
1475 : : /* Also find last listening backend before this one */
1476 [ # # ]: 0 : if (i < MyProcNumber)
1477 : 0 : prevListener = i;
1478 : 0 : }
1479 : 2 : QUEUE_BACKEND_POS(MyProcNumber) = max;
1480 : 2 : QUEUE_BACKEND_PID(MyProcNumber) = MyProcPid;
1481 : 2 : QUEUE_BACKEND_DBOID(MyProcNumber) = MyDatabaseId;
1482 : 2 : QUEUE_BACKEND_WAKEUP_PENDING(MyProcNumber) = false;
1483 : 2 : QUEUE_BACKEND_IS_ADVANCING(MyProcNumber) = false;
1484 : : /* Insert backend into list of listeners at correct position */
1485 [ - + ]: 2 : if (prevListener != INVALID_PROC_NUMBER)
1486 : : {
1487 : 0 : QUEUE_NEXT_LISTENER(MyProcNumber) = QUEUE_NEXT_LISTENER(prevListener);
1488 : 0 : QUEUE_NEXT_LISTENER(prevListener) = MyProcNumber;
1489 : 0 : }
1490 : : else
1491 : : {
1492 : 2 : QUEUE_NEXT_LISTENER(MyProcNumber) = QUEUE_FIRST_LISTENER;
1493 : 2 : QUEUE_FIRST_LISTENER = MyProcNumber;
1494 : : }
1495 : 2 : LWLockRelease(NotifyQueueLock);
1496 : :
1497 : : /* Now we are listed in the global array, so remember we're listening */
1498 : 2 : amRegisteredListener = true;
1499 : :
1500 : : /*
1501 : : * Try to move our pointer forward as far as possible. This will skip
1502 : : * over already-committed notifications, which we want to do because they
1503 : : * might be quite stale. Note that we are not yet listening on anything,
1504 : : * so we won't deliver such notifications to our frontend. Also, although
1505 : : * our transaction might have executed NOTIFY, those message(s) aren't
1506 : : * queued yet so we won't skip them here.
1507 : : */
1508 [ + - + + ]: 2 : if (!QUEUE_POS_EQUAL(max, head))
1509 : 1 : asyncQueueReadAllNotifications();
1510 [ - + ]: 2 : }
1511 : :
1512 : : /*
1513 : : * PrepareTableEntriesForListen --- subroutine for PreCommit_Notify
1514 : : *
1515 : : * Prepare a LISTEN by recording it in pendingListenActions, pre-allocating
1516 : : * an entry in localChannelTable, and pre-allocating an entry in the shared
1517 : : * globalChannelTable with listening=false. The listening flag will be set
1518 : : * to true in AtCommit_Notify. If we abort later, unwanted table entries
1519 : : * will be removed.
1520 : : */
1521 : : static void
1522 : 2 : PrepareTableEntriesForListen(const char *channel)
1523 : : {
1524 : 2 : GlobalChannelKey key;
1525 : 2 : GlobalChannelEntry *entry;
1526 : 2 : bool found;
1527 : 2 : ListenerEntry *listeners;
1528 : 2 : PendingListenEntry *pending;
1529 : :
1530 : : /*
1531 : : * Record in local pending hash that we want to LISTEN, overwriting any
1532 : : * earlier attempt to UNLISTEN.
1533 : : */
1534 : 2 : pending = (PendingListenEntry *)
1535 : 2 : hash_search(pendingListenActions, channel, HASH_ENTER, NULL);
1536 : 2 : pending->action = PENDING_LISTEN;
1537 : :
1538 : : /*
1539 : : * Ensure that there is an entry for the channel in localChannelTable.
1540 : : * (Should this fail, we can just roll back.) If the transaction fails
1541 : : * after this point, we will remove the entry if appropriate during
1542 : : * ApplyPendingListenActions. Note that this entry allows IsListeningOn()
1543 : : * to return TRUE; we assume nothing is going to consult that before
1544 : : * AtCommit_Notify/AtAbort_Notify. However, if later actions attempt to
1545 : : * UNLISTEN this channel or UNLISTEN *, we need to have the local entry
1546 : : * present to ensure they do the right things; see
1547 : : * PrepareTableEntriesForUnlisten and PrepareTableEntriesForUnlistenAll.
1548 : : */
1549 : 2 : (void) hash_search(localChannelTable, channel, HASH_ENTER, NULL);
1550 : :
1551 : : /* Pre-allocate entry in shared globalChannelTable with listening=false */
1552 : 2 : GlobalChannelKeyInit(&key, MyDatabaseId, channel);
1553 : 2 : entry = dshash_find_or_insert(globalChannelTable, &key, &found);
1554 : :
1555 [ - + ]: 2 : if (!found)
1556 : : {
1557 : : /* New channel entry, so initialize it to a safe state */
1558 : 2 : entry->listenersArray = InvalidDsaPointer;
1559 : 2 : entry->numListeners = 0;
1560 : 2 : entry->allocatedListeners = 0;
1561 : 2 : }
1562 : :
1563 : : /*
1564 : : * Create listenersArray if entry doesn't have one. It's tempting to fold
1565 : : * this into the !found case, but this coding allows us to cope in case
1566 : : * dsa_allocate() failed in an earlier attempt.
1567 : : */
1568 [ - + ]: 2 : if (!DsaPointerIsValid(entry->listenersArray))
1569 : : {
1570 : 2 : entry->listenersArray = dsa_allocate(globalChannelDSA,
1571 : : sizeof(ListenerEntry) * INITIAL_LISTENERS_ARRAY_SIZE);
1572 : 2 : entry->allocatedListeners = INITIAL_LISTENERS_ARRAY_SIZE;
1573 : 2 : }
1574 : :
1575 : 2 : listeners = (ListenerEntry *)
1576 : 2 : dsa_get_address(globalChannelDSA, entry->listenersArray);
1577 : :
1578 : : /*
1579 : : * Check if we already have a ListenerEntry (possibly from earlier in this
1580 : : * transaction)
1581 : : */
1582 [ - + - + ]: 2 : for (int i = 0; i < entry->numListeners; i++)
1583 : : {
1584 [ # # ]: 0 : if (listeners[i].procNo == MyProcNumber)
1585 : : {
1586 : : /* Already have an entry; listening flag stays as-is until commit */
1587 : 0 : dshash_release_lock(globalChannelTable, entry);
1588 : 0 : return;
1589 : : }
1590 : 0 : }
1591 : :
1592 : : /* Need to add a new entry; grow array if necessary */
1593 [ + - ]: 2 : if (entry->numListeners >= entry->allocatedListeners)
1594 : : {
1595 : 0 : int new_size = entry->allocatedListeners * 2;
1596 : 0 : dsa_pointer old_array = entry->listenersArray;
1597 : 0 : dsa_pointer new_array = dsa_allocate(globalChannelDSA,
1598 : : sizeof(ListenerEntry) * new_size);
1599 : 0 : ListenerEntry *new_listeners = (ListenerEntry *) dsa_get_address(globalChannelDSA, new_array);
1600 : :
1601 : 0 : memcpy(new_listeners, listeners, sizeof(ListenerEntry) * entry->numListeners);
1602 : 0 : entry->listenersArray = new_array;
1603 : 0 : entry->allocatedListeners = new_size;
1604 : 0 : dsa_free(globalChannelDSA, old_array);
1605 : 0 : listeners = new_listeners;
1606 : 0 : }
1607 : :
1608 : 2 : listeners[entry->numListeners].procNo = MyProcNumber;
1609 : 2 : listeners[entry->numListeners].listening = false; /* staged, not yet
1610 : : * committed */
1611 : 2 : entry->numListeners++;
1612 : :
1613 : 2 : dshash_release_lock(globalChannelTable, entry);
1614 [ - + ]: 2 : }
1615 : :
1616 : : /*
1617 : : * PrepareTableEntriesForUnlisten --- subroutine for PreCommit_Notify
1618 : : *
1619 : : * Prepare an UNLISTEN by recording it in pendingListenActions, but only if
1620 : : * we're currently listening (committed or staged). We don't touch
1621 : : * globalChannelTable yet - the listener keeps receiving signals until
1622 : : * commit, when the entry is removed.
1623 : : */
1624 : : static void
1625 : 1 : PrepareTableEntriesForUnlisten(const char *channel)
1626 : : {
1627 : 1 : PendingListenEntry *pending;
1628 : :
1629 : : /*
1630 : : * If the channel name is not in localChannelTable, then we are neither
1631 : : * listening on it nor preparing to listen on it, so we don't need to
1632 : : * record an UNLISTEN action.
1633 : : */
1634 [ + - ]: 1 : Assert(localChannelTable != NULL);
1635 [ + - ]: 1 : if (hash_search(localChannelTable, channel, HASH_FIND, NULL) == NULL)
1636 : 0 : return;
1637 : :
1638 : : /*
1639 : : * Record in local pending hash that we want to UNLISTEN, overwriting any
1640 : : * earlier attempt to LISTEN. Don't touch localChannelTable or
1641 : : * globalChannelTable yet - we keep receiving signals until commit.
1642 : : */
1643 : 1 : pending = (PendingListenEntry *)
1644 : 1 : hash_search(pendingListenActions, channel, HASH_ENTER, NULL);
1645 : 1 : pending->action = PENDING_UNLISTEN;
1646 [ - + ]: 1 : }
1647 : :
1648 : : /*
1649 : : * PrepareTableEntriesForUnlistenAll --- subroutine for PreCommit_Notify
1650 : : *
1651 : : * Prepare UNLISTEN * by recording an UNLISTEN for all listened or
1652 : : * about-to-be-listened channels in pendingListenActions.
1653 : : */
1654 : : static void
1655 : 2 : PrepareTableEntriesForUnlistenAll(void)
1656 : : {
1657 : 2 : HASH_SEQ_STATUS seq;
1658 : 2 : ChannelName *channelEntry;
1659 : 2 : PendingListenEntry *pending;
1660 : :
1661 : : /*
1662 : : * Scan localChannelTable, which will have the names of all channels that
1663 : : * we are listening on or have prepared to listen on. Record an UNLISTEN
1664 : : * action for each one, overwriting any earlier attempt to LISTEN.
1665 : : */
1666 : 2 : hash_seq_init(&seq, localChannelTable);
1667 [ + + ]: 3 : while ((channelEntry = (ChannelName *) hash_seq_search(&seq)) != NULL)
1668 : : {
1669 : 1 : pending = (PendingListenEntry *)
1670 : 1 : hash_search(pendingListenActions, channelEntry->channel, HASH_ENTER, NULL);
1671 : 1 : pending->action = PENDING_UNLISTEN;
1672 : : }
1673 : 2 : }
1674 : :
1675 : : /*
1676 : : * RemoveListenerFromChannel --- remove idx'th listener from global channel entry
1677 : : *
1678 : : * Decrements numListeners, compacts the array, and frees the entry if empty.
1679 : : * Sets *entry_ptr to NULL if the entry was deleted.
1680 : : *
1681 : : * We could get the listeners pointer from the entry, but all callers
1682 : : * already have it at hand.
1683 : : */
1684 : : static void
1685 : 2 : RemoveListenerFromChannel(GlobalChannelEntry **entry_ptr,
1686 : : ListenerEntry *listeners,
1687 : : int idx)
1688 : : {
1689 : 2 : GlobalChannelEntry *entry = *entry_ptr;
1690 : :
1691 : 2 : entry->numListeners--;
1692 [ + - ]: 2 : if (idx < entry->numListeners)
1693 : 0 : memmove(&listeners[idx], &listeners[idx + 1],
1694 : : sizeof(ListenerEntry) * (entry->numListeners - idx));
1695 : :
1696 [ - + ]: 2 : if (entry->numListeners == 0)
1697 : : {
1698 : 2 : dsa_free(globalChannelDSA, entry->listenersArray);
1699 : 2 : dshash_delete_entry(globalChannelTable, entry);
1700 : : /* tells caller not to release the entry's lock: */
1701 : 2 : *entry_ptr = NULL;
1702 : 2 : }
1703 : 2 : }
1704 : :
1705 : : /*
1706 : : * ApplyPendingListenActions
1707 : : *
1708 : : * Apply, or revert, staged listen/unlisten changes to the local and global
1709 : : * hash tables.
1710 : : */
1711 : : static void
1712 : 7025 : ApplyPendingListenActions(bool isCommit)
1713 : : {
1714 : 7025 : HASH_SEQ_STATUS seq;
1715 : 7025 : PendingListenEntry *pending;
1716 : :
1717 : : /* Quick exit if nothing to do */
1718 [ + + ]: 7025 : if (pendingListenActions == NULL)
1719 : 7020 : return;
1720 : :
1721 : : /* We made a globalChannelTable before building pendingListenActions */
1722 [ + - ]: 5 : if (globalChannelTable == NULL)
1723 [ # # # # ]: 0 : elog(PANIC, "global channel table missing post-commit/abort");
1724 : :
1725 : : /* For each staged action ... */
1726 : 5 : hash_seq_init(&seq, pendingListenActions);
1727 [ + + ]: 9 : while ((pending = (PendingListenEntry *) hash_seq_search(&seq)) != NULL)
1728 : : {
1729 : 4 : GlobalChannelKey key;
1730 : 4 : GlobalChannelEntry *entry;
1731 : 4 : bool removeLocal = true;
1732 : 4 : bool foundListener = false;
1733 : :
1734 : : /*
1735 : : * Find the global entry for this channel. If isCommit, it had better
1736 : : * exist (it was created in PreCommit). In an abort, it might not
1737 : : * exist, in which case we are not listening and should discard any
1738 : : * local entry that PreCommit may have managed to create.
1739 : : */
1740 : 4 : GlobalChannelKeyInit(&key, MyDatabaseId, pending->channel);
1741 : 4 : entry = dshash_find(globalChannelTable, &key, true);
1742 [ - + ]: 4 : if (entry != NULL)
1743 : : {
1744 : : /* Scan entry to find the ListenerEntry for this backend */
1745 : 4 : ListenerEntry *listeners;
1746 : :
1747 : 4 : listeners = (ListenerEntry *)
1748 : 4 : dsa_get_address(globalChannelDSA, entry->listenersArray);
1749 : :
1750 [ + - ]: 8 : for (int i = 0; i < entry->numListeners; i++)
1751 : : {
1752 [ - + ]: 4 : if (listeners[i].procNo != MyProcNumber)
1753 : 0 : continue;
1754 : 4 : foundListener = true;
1755 [ + - ]: 4 : if (isCommit)
1756 : : {
1757 [ + + ]: 4 : if (pending->action == PENDING_LISTEN)
1758 : : {
1759 : : /*
1760 : : * LISTEN being committed: set listening=true.
1761 : : * localChannelTable entry was created during
1762 : : * PreCommit and should be kept.
1763 : : */
1764 : 2 : listeners[i].listening = true;
1765 : 2 : removeLocal = false;
1766 : 2 : }
1767 : : else
1768 : : {
1769 : : /*
1770 : : * UNLISTEN being committed: remove pre-allocated
1771 : : * entries from both tables.
1772 : : */
1773 : 2 : RemoveListenerFromChannel(&entry, listeners, i);
1774 : : }
1775 : 4 : }
1776 : : else
1777 : : {
1778 : : /*
1779 : : * Note: this part is reachable only if the transaction
1780 : : * aborts after PreCommit_Notify() has made some
1781 : : * pendingListenActions entries, so it's pretty hard to
1782 : : * test.
1783 : : */
1784 [ # # ]: 0 : if (!listeners[i].listening)
1785 : : {
1786 : : /*
1787 : : * Staged LISTEN (or LISTEN+UNLISTEN) being aborted,
1788 : : * and we weren't listening before, so remove
1789 : : * pre-allocated entries from both tables.
1790 : : */
1791 : 0 : RemoveListenerFromChannel(&entry, listeners, i);
1792 : 0 : }
1793 : : else
1794 : : {
1795 : : /*
1796 : : * We're aborting, but the previous state was that
1797 : : * we're listening, so keep localChannelTable entry.
1798 : : */
1799 : 0 : removeLocal = false;
1800 : : }
1801 : : }
1802 : 4 : break; /* there shouldn't be another match */
1803 : : }
1804 : :
1805 : : /* We might have already released the entry by removing it */
1806 [ + + ]: 4 : if (entry != NULL)
1807 : 2 : dshash_release_lock(globalChannelTable, entry);
1808 : 4 : }
1809 : :
1810 : : /*
1811 : : * If we're committing a LISTEN action, we should have found a
1812 : : * matching ListenerEntry, but otherwise it's okay if we didn't.
1813 : : */
1814 [ + - + + : 4 : if (isCommit && pending->action == PENDING_LISTEN && !foundListener)
+ - ]
1815 [ # # # # ]: 0 : elog(PANIC, "could not find listener entry for channel \"%s\" backend %d",
1816 : : pending->channel, MyProcNumber);
1817 : :
1818 : : /*
1819 : : * If we did not find a globalChannelTable entry for our backend, or
1820 : : * if we are unlistening, remove any localChannelTable entry that may
1821 : : * exist. (Note in particular that this cleans up if we created a
1822 : : * localChannelTable entry and then failed while trying to create a
1823 : : * globalChannelTable entry.)
1824 : : */
1825 [ + + + - ]: 4 : if (removeLocal && localChannelTable != NULL)
1826 : 2 : (void) hash_search(localChannelTable, pending->channel,
1827 : : HASH_REMOVE, NULL);
1828 : 4 : }
1829 [ - + ]: 7025 : }
1830 : :
1831 : : /*
1832 : : * CleanupListenersOnExit --- called from Async_UnlistenOnExit
1833 : : *
1834 : : * Remove this backend from all channels in the shared global table.
1835 : : */
1836 : : static void
1837 : 2 : CleanupListenersOnExit(void)
1838 : : {
1839 : 2 : dshash_seq_status status;
1840 : 2 : GlobalChannelEntry *entry;
1841 : :
1842 [ + - ]: 2 : if (Trace_notify)
1843 [ # # # # ]: 0 : elog(DEBUG1, "CleanupListenersOnExit(%d)", MyProcPid);
1844 : :
1845 : : /* Clear our local cache (not really necessary, but be consistent) */
1846 [ + - ]: 2 : if (localChannelTable != NULL)
1847 : : {
1848 : 2 : hash_destroy(localChannelTable);
1849 : 2 : localChannelTable = NULL;
1850 : 2 : }
1851 : :
1852 : : /* Now remove our entries from the shared globalChannelTable */
1853 [ + - ]: 2 : if (globalChannelTable == NULL)
1854 : 0 : return;
1855 : :
1856 : 2 : dshash_seq_init(&status, globalChannelTable, true);
1857 [ - + ]: 2 : while ((entry = dshash_seq_next(&status)) != NULL)
1858 : : {
1859 : 0 : ListenerEntry *listeners;
1860 : :
1861 [ # # ]: 0 : if (entry->key.dboid != MyDatabaseId)
1862 : 0 : continue; /* not relevant */
1863 : :
1864 : 0 : listeners = (ListenerEntry *)
1865 : 0 : dsa_get_address(globalChannelDSA, entry->listenersArray);
1866 : :
1867 [ # # ]: 0 : for (int i = 0; i < entry->numListeners; i++)
1868 : : {
1869 [ # # ]: 0 : if (listeners[i].procNo == MyProcNumber)
1870 : : {
1871 : 0 : entry->numListeners--;
1872 [ # # ]: 0 : if (i < entry->numListeners)
1873 : 0 : memmove(&listeners[i], &listeners[i + 1],
1874 : : sizeof(ListenerEntry) * (entry->numListeners - i));
1875 : :
1876 [ # # ]: 0 : if (entry->numListeners == 0)
1877 : : {
1878 : 0 : dsa_free(globalChannelDSA, entry->listenersArray);
1879 : 0 : dshash_delete_current(&status);
1880 : 0 : }
1881 : 0 : break;
1882 : : }
1883 : 0 : }
1884 [ # # ]: 0 : }
1885 : 2 : dshash_seq_term(&status);
1886 : 2 : }
1887 : :
1888 : : /*
1889 : : * Test whether we are actively listening on the given channel name.
1890 : : *
1891 : : * Note: this function is executed for every notification found in the queue.
1892 : : */
1893 : : static bool
1894 : 0 : IsListeningOn(const char *channel)
1895 : : {
1896 [ # # ]: 0 : if (localChannelTable == NULL)
1897 : 0 : return false;
1898 : :
1899 : 0 : return (hash_search(localChannelTable, channel, HASH_FIND, NULL) != NULL);
1900 : 0 : }
1901 : :
1902 : : /*
1903 : : * Remove our entry from the listeners array when we are no longer listening
1904 : : * on any channel. NB: must not fail if we're already not listening.
1905 : : */
1906 : : static void
1907 : 4 : asyncQueueUnregister(void)
1908 : : {
1909 [ + + + - ]: 4 : Assert(LocalChannelTableIsEmpty()); /* else caller error */
1910 : :
1911 [ + + ]: 4 : if (!amRegisteredListener) /* nothing to do */
1912 : 2 : return;
1913 : :
1914 : : /*
1915 : : * Need exclusive lock here to manipulate list links.
1916 : : */
1917 : 2 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
1918 : : /* Mark our entry as invalid */
1919 : 2 : QUEUE_BACKEND_PID(MyProcNumber) = InvalidPid;
1920 : 2 : QUEUE_BACKEND_DBOID(MyProcNumber) = InvalidOid;
1921 : 2 : QUEUE_BACKEND_WAKEUP_PENDING(MyProcNumber) = false;
1922 : 2 : QUEUE_BACKEND_IS_ADVANCING(MyProcNumber) = false;
1923 : : /* and remove it from the list */
1924 [ + - ]: 2 : if (QUEUE_FIRST_LISTENER == MyProcNumber)
1925 : 2 : QUEUE_FIRST_LISTENER = QUEUE_NEXT_LISTENER(MyProcNumber);
1926 : : else
1927 : : {
1928 [ # # ]: 0 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
1929 : : {
1930 [ # # ]: 0 : if (QUEUE_NEXT_LISTENER(i) == MyProcNumber)
1931 : : {
1932 : 0 : QUEUE_NEXT_LISTENER(i) = QUEUE_NEXT_LISTENER(MyProcNumber);
1933 : 0 : break;
1934 : : }
1935 : 0 : }
1936 : : }
1937 : 2 : QUEUE_NEXT_LISTENER(MyProcNumber) = INVALID_PROC_NUMBER;
1938 : 2 : LWLockRelease(NotifyQueueLock);
1939 : :
1940 : : /* mark ourselves as no longer listed in the global array */
1941 : 2 : amRegisteredListener = false;
1942 : 4 : }
1943 : :
1944 : : /*
1945 : : * Test whether there is room to insert more notification messages.
1946 : : *
1947 : : * Caller must hold at least shared NotifyQueueLock.
1948 : : */
1949 : : static bool
1950 : 4 : asyncQueueIsFull(void)
1951 : : {
1952 : 4 : int64 headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
1953 : 4 : int64 tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
1954 : 4 : int64 occupied = headPage - tailPage;
1955 : :
1956 : 8 : return occupied >= max_notify_queue_pages;
1957 : 4 : }
1958 : :
1959 : : /*
1960 : : * Advance the QueuePosition to the next entry, assuming that the current
1961 : : * entry is of length entryLength. If we jump to a new page the function
1962 : : * returns true, else false.
1963 : : */
1964 : : static bool
1965 : 8 : asyncQueueAdvance(volatile QueuePosition *position, int entryLength)
1966 : : {
1967 : 8 : int64 pageno = QUEUE_POS_PAGE(*position);
1968 : 8 : int offset = QUEUE_POS_OFFSET(*position);
1969 : 8 : bool pageJump = false;
1970 : :
1971 : : /*
1972 : : * Move to the next writing position: First jump over what we have just
1973 : : * written or read.
1974 : : */
1975 : 8 : offset += entryLength;
1976 [ + - ]: 8 : Assert(offset <= QUEUE_PAGESIZE);
1977 : :
1978 : : /*
1979 : : * In a second step check if another entry can possibly be written to the
1980 : : * page. If so, stay here, we have reached the next position. If not, then
1981 : : * we need to move on to the next page.
1982 : : */
1983 [ + - ]: 8 : if (offset + QUEUEALIGN(AsyncQueueEntryEmptySize) > QUEUE_PAGESIZE)
1984 : : {
1985 : 0 : pageno++;
1986 : 0 : offset = 0;
1987 : 0 : pageJump = true;
1988 : 0 : }
1989 : :
1990 : 8 : SET_QUEUE_POS(*position, pageno, offset);
1991 : 16 : return pageJump;
1992 : 8 : }
1993 : :
1994 : : /*
1995 : : * Fill the AsyncQueueEntry at *qe with an outbound notification message.
1996 : : */
1997 : : static void
1998 : 4 : asyncQueueNotificationToEntry(Notification *n, AsyncQueueEntry *qe)
1999 : : {
2000 : 4 : size_t channellen = n->channel_len;
2001 : 4 : size_t payloadlen = n->payload_len;
2002 : 4 : int entryLength;
2003 : :
2004 [ + - ]: 4 : Assert(channellen < NAMEDATALEN);
2005 [ + - ]: 4 : Assert(payloadlen < NOTIFY_PAYLOAD_MAX_LENGTH);
2006 : :
2007 : : /* The terminators are already included in AsyncQueueEntryEmptySize */
2008 : 4 : entryLength = AsyncQueueEntryEmptySize + payloadlen + channellen;
2009 : 4 : entryLength = QUEUEALIGN(entryLength);
2010 : 4 : qe->length = entryLength;
2011 : 4 : qe->dboid = MyDatabaseId;
2012 : 4 : qe->xid = GetCurrentTransactionId();
2013 : 4 : qe->srcPid = MyProcPid;
2014 : 4 : memcpy(qe->data, n->data, channellen + payloadlen + 2);
2015 : 4 : }
2016 : :
2017 : : /*
2018 : : * Add pending notifications to the queue.
2019 : : *
2020 : : * We go page by page here, i.e. we stop once we have to go to a new page but
2021 : : * we will be called again and then fill that next page. If an entry does not
2022 : : * fit into the current page, we write a dummy entry with an InvalidOid as the
2023 : : * database OID in order to fill the page. So every page is always used up to
2024 : : * the last byte which simplifies reading the page later.
2025 : : *
2026 : : * We are passed the list cell (in pendingNotifies->events) containing the next
2027 : : * notification to write and return the first still-unwritten cell back.
2028 : : * Eventually we will return NULL indicating all is done.
2029 : : *
2030 : : * We are holding NotifyQueueLock already from the caller and grab
2031 : : * page specific SLRU bank lock locally in this function.
2032 : : */
2033 : : static ListCell *
2034 : 4 : asyncQueueAddEntries(ListCell *nextNotify)
2035 : : {
2036 : 4 : AsyncQueueEntry qe;
2037 : 4 : QueuePosition queue_head;
2038 : 4 : int64 pageno;
2039 : 4 : int offset;
2040 : 4 : int slotno;
2041 : 4 : LWLock *prevlock;
2042 : :
2043 : : /*
2044 : : * We work with a local copy of QUEUE_HEAD, which we write back to shared
2045 : : * memory upon exiting. The reason for this is that if we have to advance
2046 : : * to a new page, SimpleLruZeroPage might fail (out of disk space, for
2047 : : * instance), and we must not advance QUEUE_HEAD if it does. (Otherwise,
2048 : : * subsequent insertions would try to put entries into a page that slru.c
2049 : : * thinks doesn't exist yet.) So, use a local position variable. Note
2050 : : * that if we do fail, any already-inserted queue entries are forgotten;
2051 : : * this is okay, since they'd be useless anyway after our transaction
2052 : : * rolls back.
2053 : : */
2054 : 4 : queue_head = QUEUE_HEAD;
2055 : :
2056 : : /*
2057 : : * If this is the first write since the postmaster started, we need to
2058 : : * initialize the first page of the async SLRU. Otherwise, the current
2059 : : * page should be initialized already, so just fetch it.
2060 : : */
2061 : 4 : pageno = QUEUE_POS_PAGE(queue_head);
2062 : 4 : prevlock = SimpleLruGetBankLock(NotifyCtl, pageno);
2063 : :
2064 : : /* We hold both NotifyQueueLock and SLRU bank lock during this operation */
2065 : 4 : LWLockAcquire(prevlock, LW_EXCLUSIVE);
2066 : :
2067 [ + - + + ]: 4 : if (QUEUE_POS_IS_ZERO(queue_head))
2068 : 1 : slotno = SimpleLruZeroPage(NotifyCtl, pageno);
2069 : : else
2070 : 3 : slotno = SimpleLruReadPage(NotifyCtl, pageno, true,
2071 : : InvalidTransactionId);
2072 : :
2073 : : /* Note we mark the page dirty before writing in it */
2074 : 4 : NotifyCtl->shared->page_dirty[slotno] = true;
2075 : :
2076 [ + + ]: 8 : while (nextNotify != NULL)
2077 : : {
2078 : 4 : Notification *n = (Notification *) lfirst(nextNotify);
2079 : :
2080 : : /* Construct a valid queue entry in local variable qe */
2081 : 4 : asyncQueueNotificationToEntry(n, &qe);
2082 : :
2083 : 4 : offset = QUEUE_POS_OFFSET(queue_head);
2084 : :
2085 : : /* Check whether the entry really fits on the current page */
2086 [ + - ]: 4 : if (offset + qe.length <= QUEUE_PAGESIZE)
2087 : : {
2088 : : /* OK, so advance nextNotify past this item */
2089 : 4 : nextNotify = lnext(pendingNotifies->events, nextNotify);
2090 : 4 : }
2091 : : else
2092 : : {
2093 : : /*
2094 : : * Write a dummy entry to fill up the page. Actually readers will
2095 : : * only check dboid and since it won't match any reader's database
2096 : : * OID, they will ignore this entry and move on.
2097 : : */
2098 : 0 : qe.length = QUEUE_PAGESIZE - offset;
2099 : 0 : qe.dboid = InvalidOid;
2100 : 0 : qe.xid = InvalidTransactionId;
2101 : 0 : qe.data[0] = '\0'; /* empty channel */
2102 : 0 : qe.data[1] = '\0'; /* empty payload */
2103 : : }
2104 : :
2105 : : /* Now copy qe into the shared buffer page */
2106 : 4 : memcpy(NotifyCtl->shared->page_buffer[slotno] + offset,
2107 : : &qe,
2108 : : qe.length);
2109 : :
2110 : : /* Advance queue_head appropriately, and detect if page is full */
2111 [ - + ]: 4 : if (asyncQueueAdvance(&(queue_head), qe.length))
2112 : : {
2113 : 0 : LWLock *lock;
2114 : :
2115 : 0 : pageno = QUEUE_POS_PAGE(queue_head);
2116 : 0 : lock = SimpleLruGetBankLock(NotifyCtl, pageno);
2117 [ # # ]: 0 : if (lock != prevlock)
2118 : : {
2119 : 0 : LWLockRelease(prevlock);
2120 : 0 : LWLockAcquire(lock, LW_EXCLUSIVE);
2121 : 0 : prevlock = lock;
2122 : 0 : }
2123 : :
2124 : : /*
2125 : : * Page is full, so we're done here, but first fill the next page
2126 : : * with zeroes. The reason to do this is to ensure that slru.c's
2127 : : * idea of the head page is always the same as ours, which avoids
2128 : : * boundary problems in SimpleLruTruncate. The test in
2129 : : * asyncQueueIsFull() ensured that there is room to create this
2130 : : * page without overrunning the queue.
2131 : : */
2132 : 0 : slotno = SimpleLruZeroPage(NotifyCtl, QUEUE_POS_PAGE(queue_head));
2133 : :
2134 : : /*
2135 : : * If the new page address is a multiple of QUEUE_CLEANUP_DELAY,
2136 : : * set flag to remember that we should try to advance the tail
2137 : : * pointer (we don't want to actually do that right here).
2138 : : */
2139 [ # # ]: 0 : if (QUEUE_POS_PAGE(queue_head) % QUEUE_CLEANUP_DELAY == 0)
2140 : 0 : tryAdvanceTail = true;
2141 : :
2142 : : /* And exit the loop */
2143 : : break;
2144 : 0 : }
2145 [ - - + ]: 4 : }
2146 : :
2147 : : /* Success, so update the global QUEUE_HEAD */
2148 : 4 : QUEUE_HEAD = queue_head;
2149 : :
2150 : 4 : LWLockRelease(prevlock);
2151 : :
2152 : 8 : return nextNotify;
2153 : 4 : }
2154 : :
2155 : : /*
2156 : : * SQL function to return the fraction of the notification queue currently
2157 : : * occupied.
2158 : : */
2159 : : Datum
2160 : 1 : pg_notification_queue_usage(PG_FUNCTION_ARGS)
2161 : : {
2162 : 1 : double usage;
2163 : :
2164 : : /* Advance the queue tail so we don't report a too-large result */
2165 : 1 : asyncQueueAdvanceTail();
2166 : :
2167 : 1 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
2168 : 1 : usage = asyncQueueUsage();
2169 : 1 : LWLockRelease(NotifyQueueLock);
2170 : :
2171 : 2 : PG_RETURN_FLOAT8(usage);
2172 : 1 : }
2173 : :
2174 : : /*
2175 : : * Return the fraction of the queue that is currently occupied.
2176 : : *
2177 : : * The caller must hold NotifyQueueLock in (at least) shared mode.
2178 : : *
2179 : : * Note: we measure the distance to the logical tail page, not the physical
2180 : : * tail page. In some sense that's wrong, but the relative position of the
2181 : : * physical tail is affected by details such as SLRU segment boundaries,
2182 : : * so that a result based on that is unpleasantly unstable.
2183 : : */
2184 : : static double
2185 : 5 : asyncQueueUsage(void)
2186 : : {
2187 : 5 : int64 headPage = QUEUE_POS_PAGE(QUEUE_HEAD);
2188 : 5 : int64 tailPage = QUEUE_POS_PAGE(QUEUE_TAIL);
2189 : 5 : int64 occupied = headPage - tailPage;
2190 : :
2191 [ - + ]: 5 : if (occupied == 0)
2192 : 5 : return (double) 0; /* fast exit for common case */
2193 : :
2194 : 0 : return (double) occupied / (double) max_notify_queue_pages;
2195 : 5 : }
2196 : :
2197 : : /*
2198 : : * Check whether the queue is at least half full, and emit a warning if so.
2199 : : *
2200 : : * This is unlikely given the size of the queue, but possible.
2201 : : * The warnings show up at most once every QUEUE_FULL_WARN_INTERVAL.
2202 : : *
2203 : : * Caller must hold exclusive NotifyQueueLock.
2204 : : */
2205 : : static void
2206 : 4 : asyncQueueFillWarning(void)
2207 : : {
2208 : 4 : double fillDegree;
2209 : 4 : TimestampTz t;
2210 : :
2211 : 4 : fillDegree = asyncQueueUsage();
2212 [ + - ]: 4 : if (fillDegree < 0.5)
2213 : 4 : return;
2214 : :
2215 : 0 : t = GetCurrentTimestamp();
2216 : :
2217 [ # # # # ]: 0 : if (TimestampDifferenceExceeds(asyncQueueControl->lastQueueFillWarn,
2218 : 0 : t, QUEUE_FULL_WARN_INTERVAL))
2219 : : {
2220 : 0 : QueuePosition min = QUEUE_HEAD;
2221 : 0 : int32 minPid = InvalidPid;
2222 : :
2223 [ # # ]: 0 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
2224 : : {
2225 [ # # ]: 0 : Assert(QUEUE_BACKEND_PID(i) != InvalidPid);
2226 [ # # # # : 0 : min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
# # ]
2227 [ # # # # ]: 0 : if (QUEUE_POS_EQUAL(min, QUEUE_BACKEND_POS(i)))
2228 : 0 : minPid = QUEUE_BACKEND_PID(i);
2229 : 0 : }
2230 : :
2231 [ # # # # : 0 : ereport(WARNING,
# # # # ]
2232 : : (errmsg("NOTIFY queue is %.0f%% full", fillDegree * 100),
2233 : : (minPid != InvalidPid ?
2234 : : errdetail("The server process with PID %d is among those with the oldest transactions.", minPid)
2235 : : : 0),
2236 : : (minPid != InvalidPid ?
2237 : : errhint("The NOTIFY queue cannot be emptied until that process ends its current transaction.")
2238 : : : 0)));
2239 : :
2240 : 0 : asyncQueueControl->lastQueueFillWarn = t;
2241 : 0 : }
2242 [ - + ]: 4 : }
2243 : :
2244 : : /*
2245 : : * Send signals to listening backends.
2246 : : *
2247 : : * Normally we signal only backends that are interested in the notifies that
2248 : : * we just sent. However, that will leave idle listeners falling further and
2249 : : * further behind. Waken them anyway if they're far enough behind, so they'll
2250 : : * advance their queue position pointers, allowing the global tail to advance.
2251 : : *
2252 : : * Since we know the ProcNumber and the Pid the signaling is quite cheap.
2253 : : *
2254 : : * This is called during CommitTransaction(), so it's important for it
2255 : : * to have very low probability of failure.
2256 : : */
2257 : : static void
2258 : 4 : SignalBackends(void)
2259 : : {
2260 : 4 : int count;
2261 : :
2262 : : /* Can't get here without PreCommit_Notify having made the global table */
2263 [ + - ]: 4 : Assert(globalChannelTable != NULL);
2264 : :
2265 : : /* It should have set up these arrays, too */
2266 [ + - ]: 4 : Assert(signalPids != NULL && signalProcnos != NULL);
2267 : :
2268 : : /*
2269 : : * Identify backends that we need to signal. We don't want to send
2270 : : * signals while holding the NotifyQueueLock, so this part just builds a
2271 : : * list of target PIDs in signalPids[] and signalProcnos[].
2272 : : */
2273 : 4 : count = 0;
2274 : :
2275 : 4 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
2276 : :
2277 : : /* Scan each channel name that we notified in this transaction */
2278 [ + + + - : 12 : foreach_ptr(char, channel, pendingNotifies->uniqueChannelNames)
+ + + + ]
2279 : : {
2280 : 4 : GlobalChannelKey key;
2281 : 4 : GlobalChannelEntry *entry;
2282 : 4 : ListenerEntry *listeners;
2283 : :
2284 : 4 : GlobalChannelKeyInit(&key, MyDatabaseId, channel);
2285 : 4 : entry = dshash_find(globalChannelTable, &key, false);
2286 [ - + ]: 4 : if (entry == NULL)
2287 : 4 : continue; /* nobody is listening */
2288 : :
2289 : 0 : listeners = (ListenerEntry *) dsa_get_address(globalChannelDSA,
2290 : 0 : entry->listenersArray);
2291 : :
2292 : : /* Identify listeners that now need waking, add them to arrays */
2293 [ # # ]: 0 : for (int j = 0; j < entry->numListeners; j++)
2294 : : {
2295 : 0 : ProcNumber i;
2296 : 0 : int32 pid;
2297 : 0 : QueuePosition pos;
2298 : :
2299 [ # # ]: 0 : if (!listeners[j].listening)
2300 : 0 : continue; /* ignore not-yet-committed listeners */
2301 : :
2302 : 0 : i = listeners[j].procNo;
2303 : :
2304 [ # # ]: 0 : if (QUEUE_BACKEND_WAKEUP_PENDING(i))
2305 : 0 : continue; /* already signaled, no need to repeat */
2306 : :
2307 : 0 : pid = QUEUE_BACKEND_PID(i);
2308 : 0 : pos = QUEUE_BACKEND_POS(i);
2309 : :
2310 [ # # # # ]: 0 : if (QUEUE_POS_EQUAL(pos, QUEUE_HEAD))
2311 : 0 : continue; /* it's fully caught up already */
2312 : :
2313 [ # # ]: 0 : Assert(pid != InvalidPid);
2314 : :
2315 : 0 : QUEUE_BACKEND_WAKEUP_PENDING(i) = true;
2316 : 0 : signalPids[count] = pid;
2317 : 0 : signalProcnos[count] = i;
2318 : 0 : count++;
2319 [ # # ]: 0 : }
2320 : :
2321 : 0 : dshash_release_lock(globalChannelTable, entry);
2322 [ + - ]: 8 : }
2323 : :
2324 : : /*
2325 : : * Scan all listeners. Any that are not already pending wakeup must not
2326 : : * be interested in our notifications (else we'd have set their wakeup
2327 : : * flags above). Check to see if we can directly advance their queue
2328 : : * pointers to save a wakeup. Otherwise, if they are far behind, wake
2329 : : * them anyway so they will catch up.
2330 : : */
2331 [ - + ]: 4 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
2332 : : {
2333 : 0 : int32 pid;
2334 : 0 : QueuePosition pos;
2335 : :
2336 [ # # ]: 0 : if (QUEUE_BACKEND_WAKEUP_PENDING(i))
2337 : 0 : continue;
2338 : :
2339 : : /* If it's currently advancing, we should not touch it */
2340 [ # # ]: 0 : if (QUEUE_BACKEND_IS_ADVANCING(i))
2341 : 0 : continue;
2342 : :
2343 : 0 : pid = QUEUE_BACKEND_PID(i);
2344 : 0 : pos = QUEUE_BACKEND_POS(i);
2345 : :
2346 : : /*
2347 : : * We can directly advance the other backend's queue pointer if it's
2348 : : * not currently advancing (else there are race conditions), and its
2349 : : * current pointer is not behind queueHeadBeforeWrite (else we'd make
2350 : : * it miss some older messages), and we'd not be moving the pointer
2351 : : * backward.
2352 : : */
2353 [ # # # # : 0 : if (!QUEUE_POS_PRECEDES(pos, queueHeadBeforeWrite) &&
# # ]
2354 [ # # # # ]: 0 : QUEUE_POS_PRECEDES(pos, queueHeadAfterWrite))
2355 : : {
2356 : : /* We can directly advance its pointer past what we wrote */
2357 : 0 : QUEUE_BACKEND_POS(i) = queueHeadAfterWrite;
2358 : 0 : }
2359 : 0 : else if (asyncQueuePageDiff(QUEUE_POS_PAGE(QUEUE_HEAD),
2360 [ # # # # ]: 0 : QUEUE_POS_PAGE(pos)) >= QUEUE_CLEANUP_DELAY)
2361 : : {
2362 : : /* It's idle and far behind, so wake it up */
2363 [ # # ]: 0 : Assert(pid != InvalidPid);
2364 : :
2365 : 0 : QUEUE_BACKEND_WAKEUP_PENDING(i) = true;
2366 : 0 : signalPids[count] = pid;
2367 : 0 : signalProcnos[count] = i;
2368 : 0 : count++;
2369 : 0 : }
2370 [ # # ]: 0 : }
2371 : :
2372 : 4 : LWLockRelease(NotifyQueueLock);
2373 : :
2374 : : /* Now send signals */
2375 [ - + ]: 4 : for (int i = 0; i < count; i++)
2376 : : {
2377 : 0 : int32 pid = signalPids[i];
2378 : :
2379 : : /*
2380 : : * If we are signaling our own process, no need to involve the kernel;
2381 : : * just set the flag directly.
2382 : : */
2383 [ # # ]: 0 : if (pid == MyProcPid)
2384 : : {
2385 : 0 : notifyInterruptPending = true;
2386 : 0 : continue;
2387 : : }
2388 : :
2389 : : /*
2390 : : * Note: assuming things aren't broken, a signal failure here could
2391 : : * only occur if the target backend exited since we released
2392 : : * NotifyQueueLock; which is unlikely but certainly possible. So we
2393 : : * just log a low-level debug message if it happens.
2394 : : */
2395 [ # # ]: 0 : if (SendProcSignal(pid, PROCSIG_NOTIFY_INTERRUPT, signalProcnos[i]) < 0)
2396 [ # # # # ]: 0 : elog(DEBUG3, "could not signal backend with PID %d: %m", pid);
2397 [ # # ]: 0 : }
2398 : 4 : }
2399 : :
2400 : : /*
2401 : : * AtAbort_Notify
2402 : : *
2403 : : * This is called at transaction abort.
2404 : : *
2405 : : * Revert any staged listen/unlisten changes and clean up transaction state.
2406 : : * This only does anything if we abort after PreCommit_Notify has staged
2407 : : * some entries.
2408 : : */
2409 : : void
2410 : 7016 : AtAbort_Notify(void)
2411 : : {
2412 : : /* Revert staged listen/unlisten changes */
2413 : 7016 : ApplyPendingListenActions(false);
2414 : :
2415 : : /* If we're no longer listening on anything, unregister */
2416 [ - + # # : 7016 : if (amRegisteredListener && LocalChannelTableIsEmpty())
# # ]
2417 : 0 : asyncQueueUnregister();
2418 : :
2419 : : /* And clean up */
2420 : 7016 : ClearPendingActionsAndNotifies();
2421 : 7016 : }
2422 : :
2423 : : /*
2424 : : * AtSubCommit_Notify() --- Take care of subtransaction commit.
2425 : : *
2426 : : * Reassign all items in the pending lists to the parent transaction.
2427 : : */
2428 : : void
2429 : 482 : AtSubCommit_Notify(void)
2430 : : {
2431 : 482 : int my_level = GetCurrentTransactionNestLevel();
2432 : :
2433 : : /* If there are actions at our nesting level, we must reparent them. */
2434 [ - + # # ]: 482 : if (pendingActions != NULL &&
2435 : 0 : pendingActions->nestingLevel >= my_level)
2436 : : {
2437 [ # # # # ]: 0 : if (pendingActions->upper == NULL ||
2438 : 0 : pendingActions->upper->nestingLevel < my_level - 1)
2439 : : {
2440 : : /* nothing to merge; give the whole thing to the parent */
2441 : 0 : --pendingActions->nestingLevel;
2442 : 0 : }
2443 : : else
2444 : : {
2445 : 0 : ActionList *childPendingActions = pendingActions;
2446 : :
2447 : 0 : pendingActions = pendingActions->upper;
2448 : :
2449 : : /*
2450 : : * Mustn't try to eliminate duplicates here --- see queue_listen()
2451 : : */
2452 : 0 : pendingActions->actions =
2453 : 0 : list_concat(pendingActions->actions,
2454 : 0 : childPendingActions->actions);
2455 : 0 : pfree(childPendingActions);
2456 : 0 : }
2457 : 0 : }
2458 : :
2459 : : /* If there are notifies at our nesting level, we must reparent them. */
2460 [ - + # # ]: 482 : if (pendingNotifies != NULL &&
2461 : 0 : pendingNotifies->nestingLevel >= my_level)
2462 : : {
2463 [ # # ]: 0 : Assert(pendingNotifies->nestingLevel == my_level);
2464 : :
2465 [ # # # # ]: 0 : if (pendingNotifies->upper == NULL ||
2466 : 0 : pendingNotifies->upper->nestingLevel < my_level - 1)
2467 : : {
2468 : : /* nothing to merge; give the whole thing to the parent */
2469 : 0 : --pendingNotifies->nestingLevel;
2470 : 0 : }
2471 : : else
2472 : : {
2473 : : /*
2474 : : * Formerly, we didn't bother to eliminate duplicates here, but
2475 : : * now we must, else we fall foul of "Assert(!found)", either here
2476 : : * or during a later attempt to build the parent-level hashtable.
2477 : : */
2478 : 0 : NotificationList *childPendingNotifies = pendingNotifies;
2479 : 0 : ListCell *l;
2480 : :
2481 : 0 : pendingNotifies = pendingNotifies->upper;
2482 : : /* Insert all the subxact's events into parent, except for dups */
2483 [ # # # # : 0 : foreach(l, childPendingNotifies->events)
# # ]
2484 : : {
2485 : 0 : Notification *childn = (Notification *) lfirst(l);
2486 : :
2487 [ # # ]: 0 : if (!AsyncExistsPendingNotify(childn))
2488 : 0 : AddEventToPendingNotifies(childn);
2489 : 0 : }
2490 : 0 : pfree(childPendingNotifies);
2491 : 0 : }
2492 : 0 : }
2493 : 482 : }
2494 : :
2495 : : /*
2496 : : * AtSubAbort_Notify() --- Take care of subtransaction abort.
2497 : : */
2498 : : void
2499 : 1183 : AtSubAbort_Notify(void)
2500 : : {
2501 : 1183 : int my_level = GetCurrentTransactionNestLevel();
2502 : :
2503 : : /*
2504 : : * All we have to do is pop the stack --- the actions/notifies made in
2505 : : * this subxact are no longer interesting, and the space will be freed
2506 : : * when CurTransactionContext is recycled. We still have to free the
2507 : : * ActionList and NotificationList objects themselves, though, because
2508 : : * those are allocated in TopTransactionContext.
2509 : : *
2510 : : * Note that there might be no entries at all, or no entries for the
2511 : : * current subtransaction level, either because none were ever created, or
2512 : : * because we reentered this routine due to trouble during subxact abort.
2513 : : */
2514 [ + - - + ]: 1183 : while (pendingActions != NULL &&
2515 : 0 : pendingActions->nestingLevel >= my_level)
2516 : : {
2517 : 0 : ActionList *childPendingActions = pendingActions;
2518 : :
2519 : 0 : pendingActions = pendingActions->upper;
2520 : 0 : pfree(childPendingActions);
2521 : 0 : }
2522 : :
2523 [ + - - + ]: 1183 : while (pendingNotifies != NULL &&
2524 : 0 : pendingNotifies->nestingLevel >= my_level)
2525 : : {
2526 : 0 : NotificationList *childPendingNotifies = pendingNotifies;
2527 : :
2528 : 0 : pendingNotifies = pendingNotifies->upper;
2529 : 0 : pfree(childPendingNotifies);
2530 : 0 : }
2531 : 1183 : }
2532 : :
2533 : : /*
2534 : : * HandleNotifyInterrupt
2535 : : *
2536 : : * Signal handler portion of interrupt handling. Let the backend know
2537 : : * that there's a pending notify interrupt. If we're currently reading
2538 : : * from the client, this will interrupt the read and
2539 : : * ProcessClientReadInterrupt() will call ProcessNotifyInterrupt().
2540 : : */
2541 : : void
2542 : 0 : HandleNotifyInterrupt(void)
2543 : : {
2544 : : /*
2545 : : * Note: this is called by a SIGNAL HANDLER. You must be very wary what
2546 : : * you do here.
2547 : : */
2548 : :
2549 : : /* signal that work needs to be done */
2550 : 0 : notifyInterruptPending = true;
2551 : :
2552 : : /* make sure the event is processed in due course */
2553 : 0 : SetLatch(MyLatch);
2554 : 0 : }
2555 : :
2556 : : /*
2557 : : * ProcessNotifyInterrupt
2558 : : *
2559 : : * This is called if we see notifyInterruptPending set, just before
2560 : : * transmitting ReadyForQuery at the end of a frontend command, and
2561 : : * also if a notify signal occurs while reading from the frontend.
2562 : : * HandleNotifyInterrupt() will cause the read to be interrupted
2563 : : * via the process's latch, and this routine will get called.
2564 : : * If we are truly idle (ie, *not* inside a transaction block),
2565 : : * process the incoming notifies.
2566 : : *
2567 : : * If "flush" is true, force any frontend messages out immediately.
2568 : : * This can be false when being called at the end of a frontend command,
2569 : : * since we'll flush after sending ReadyForQuery.
2570 : : */
2571 : : void
2572 : 0 : ProcessNotifyInterrupt(bool flush)
2573 : : {
2574 [ # # ]: 0 : if (IsTransactionOrTransactionBlock())
2575 : 0 : return; /* not really idle */
2576 : :
2577 : : /* Loop in case another signal arrives while sending messages */
2578 [ # # ]: 0 : while (notifyInterruptPending)
2579 : 0 : ProcessIncomingNotify(flush);
2580 : 0 : }
2581 : :
2582 : :
2583 : : /*
2584 : : * Read all pending notifications from the queue, and deliver appropriate
2585 : : * ones to my frontend. Stop when we reach queue head or an uncommitted
2586 : : * notification.
2587 : : */
2588 : : static void
2589 : 1 : asyncQueueReadAllNotifications(void)
2590 : : {
2591 : 1 : QueuePosition pos;
2592 : 1 : QueuePosition head;
2593 : 1 : Snapshot snapshot;
2594 : :
2595 : : /*
2596 : : * Fetch current state, indicate to others that we have woken up, and that
2597 : : * we are in process of advancing our position.
2598 : : */
2599 : 1 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
2600 : : /* Assert checks that we have a valid state entry */
2601 [ + - ]: 1 : Assert(MyProcPid == QUEUE_BACKEND_PID(MyProcNumber));
2602 : 1 : QUEUE_BACKEND_WAKEUP_PENDING(MyProcNumber) = false;
2603 : 1 : pos = QUEUE_BACKEND_POS(MyProcNumber);
2604 : 1 : head = QUEUE_HEAD;
2605 : :
2606 [ + - + - ]: 1 : if (QUEUE_POS_EQUAL(pos, head))
2607 : : {
2608 : : /* Nothing to do, we have read all notifications already. */
2609 : 0 : LWLockRelease(NotifyQueueLock);
2610 : 0 : return;
2611 : : }
2612 : :
2613 : 1 : QUEUE_BACKEND_IS_ADVANCING(MyProcNumber) = true;
2614 : 1 : LWLockRelease(NotifyQueueLock);
2615 : :
2616 : : /*----------
2617 : : * Get snapshot we'll use to decide which xacts are still in progress.
2618 : : * This is trickier than it might seem, because of race conditions.
2619 : : * Consider the following example:
2620 : : *
2621 : : * Backend 1: Backend 2:
2622 : : *
2623 : : * transaction starts
2624 : : * UPDATE foo SET ...;
2625 : : * NOTIFY foo;
2626 : : * commit starts
2627 : : * queue the notify message
2628 : : * transaction starts
2629 : : * LISTEN foo; -- first LISTEN in session
2630 : : * SELECT * FROM foo WHERE ...;
2631 : : * commit to clog
2632 : : * commit starts
2633 : : * add backend 2 to array of listeners
2634 : : * advance to queue head (this code)
2635 : : * commit to clog
2636 : : *
2637 : : * Transaction 2's SELECT has not seen the UPDATE's effects, since that
2638 : : * wasn't committed yet. Ideally we'd ensure that client 2 would
2639 : : * eventually get transaction 1's notify message, but there's no way
2640 : : * to do that; until we're in the listener array, there's no guarantee
2641 : : * that the notify message doesn't get removed from the queue.
2642 : : *
2643 : : * Therefore the coding technique transaction 2 is using is unsafe:
2644 : : * applications must commit a LISTEN before inspecting database state,
2645 : : * if they want to ensure they will see notifications about subsequent
2646 : : * changes to that state.
2647 : : *
2648 : : * What we do guarantee is that we'll see all notifications from
2649 : : * transactions committing after the snapshot we take here.
2650 : : * BecomeRegisteredListener has already added us to the listener array,
2651 : : * so no not-yet-committed messages can be removed from the queue
2652 : : * before we see them.
2653 : : *----------
2654 : : */
2655 : 1 : snapshot = RegisterSnapshot(GetLatestSnapshot());
2656 : :
2657 : : /*
2658 : : * It is possible that we fail while trying to send a message to our
2659 : : * frontend (for example, because of encoding conversion failure). If
2660 : : * that happens it is critical that we not try to send the same message
2661 : : * over and over again. Therefore, we set ExitOnAnyError to upgrade any
2662 : : * ERRORs to FATAL, causing the client connection to be closed on error.
2663 : : *
2664 : : * We used to only skip over the offending message and try to soldier on,
2665 : : * but it was somewhat questionable to lose a notification and give the
2666 : : * client an ERROR instead. A client application is not be prepared for
2667 : : * that and can't tell that a notification was missed. It was also not
2668 : : * very useful in practice because notifications are often processed while
2669 : : * a connection is idle and reading a message from the client, and in that
2670 : : * state, any error is upgraded to FATAL anyway. Closing the connection
2671 : : * is a clear signal to the application that it might have missed
2672 : : * notifications.
2673 : : */
2674 : : {
2675 : 1 : bool save_ExitOnAnyError = ExitOnAnyError;
2676 : 1 : bool reachedStop;
2677 : :
2678 : 1 : ExitOnAnyError = true;
2679 : :
2680 : 1 : do
2681 : : {
2682 : : /*
2683 : : * Process messages up to the stop position, end of page, or an
2684 : : * uncommitted message.
2685 : : *
2686 : : * Our stop position is what we found to be the head's position
2687 : : * when we entered this function. It might have changed already.
2688 : : * But if it has, we will receive (or have already received and
2689 : : * queued) another signal and come here again.
2690 : : *
2691 : : * We are not holding NotifyQueueLock here! The queue can only
2692 : : * extend beyond the head pointer (see above) and we leave our
2693 : : * backend's pointer where it is so nobody will truncate or
2694 : : * rewrite pages under us. Especially we don't want to hold a lock
2695 : : * while sending the notifications to the frontend.
2696 : : */
2697 : 1 : reachedStop = asyncQueueProcessPageEntries(&pos, head, snapshot);
2698 [ - + ]: 1 : } while (!reachedStop);
2699 : :
2700 : : /* Update shared state */
2701 : 1 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
2702 : 1 : QUEUE_BACKEND_POS(MyProcNumber) = pos;
2703 : 1 : QUEUE_BACKEND_IS_ADVANCING(MyProcNumber) = false;
2704 : 1 : LWLockRelease(NotifyQueueLock);
2705 : :
2706 : 1 : ExitOnAnyError = save_ExitOnAnyError;
2707 : 1 : }
2708 : :
2709 : : /* Done with snapshot */
2710 : 1 : UnregisterSnapshot(snapshot);
2711 [ - + ]: 1 : }
2712 : :
2713 : : /*
2714 : : * Fetch notifications from the shared queue, beginning at position current,
2715 : : * and deliver relevant ones to my frontend.
2716 : : *
2717 : : * The function returns true once we have reached the stop position or an
2718 : : * uncommitted notification, and false if we have finished with the page.
2719 : : * In other words: once it returns true there is no need to look further.
2720 : : * The QueuePosition *current is advanced past all processed messages.
2721 : : */
2722 : : static bool
2723 : 1 : asyncQueueProcessPageEntries(QueuePosition *current,
2724 : : QueuePosition stop,
2725 : : Snapshot snapshot)
2726 : : {
2727 : 1 : int64 curpage = QUEUE_POS_PAGE(*current);
2728 : 1 : int slotno;
2729 : 1 : char *page_buffer;
2730 : 1 : bool reachedStop = false;
2731 : 1 : bool reachedEndOfPage;
2732 : :
2733 : : /*
2734 : : * We copy the entries into a local buffer to avoid holding the SLRU lock
2735 : : * while we transmit them to our frontend. The local buffer must be
2736 : : * adequately aligned.
2737 : : */
2738 : 1 : alignas(AsyncQueueEntry) char local_buf[QUEUE_PAGESIZE];
2739 : 1 : char *local_buf_end = local_buf;
2740 : :
2741 : 1 : slotno = SimpleLruReadPage_ReadOnly(NotifyCtl, curpage,
2742 : : InvalidTransactionId);
2743 : 1 : page_buffer = NotifyCtl->shared->page_buffer[slotno];
2744 : :
2745 : 1 : do
2746 : : {
2747 : 5 : QueuePosition thisentry = *current;
2748 : 5 : AsyncQueueEntry *qe;
2749 : :
2750 [ + - + + ]: 5 : if (QUEUE_POS_EQUAL(thisentry, stop))
2751 : 1 : break;
2752 : :
2753 : 4 : qe = (AsyncQueueEntry *) (page_buffer + QUEUE_POS_OFFSET(thisentry));
2754 : :
2755 : : /*
2756 : : * Advance *current over this message, possibly to the next page. As
2757 : : * noted in the comments for asyncQueueReadAllNotifications, we must
2758 : : * do this before possibly failing while processing the message.
2759 : : */
2760 : 4 : reachedEndOfPage = asyncQueueAdvance(current, qe->length);
2761 : :
2762 : : /* Ignore messages destined for other databases */
2763 [ - + ]: 4 : if (qe->dboid == MyDatabaseId)
2764 : : {
2765 [ - + ]: 4 : if (XidInMVCCSnapshot(qe->xid, snapshot))
2766 : : {
2767 : : /*
2768 : : * The source transaction is still in progress, so we can't
2769 : : * process this message yet. Break out of the loop, but first
2770 : : * back up *current so we will reprocess the message next
2771 : : * time. (Note: it is unlikely but not impossible for
2772 : : * TransactionIdDidCommit to fail, so we can't really avoid
2773 : : * this advance-then-back-up behavior when dealing with an
2774 : : * uncommitted message.)
2775 : : *
2776 : : * Note that we must test XidInMVCCSnapshot before we test
2777 : : * TransactionIdDidCommit, else we might return a message from
2778 : : * a transaction that is not yet visible to snapshots; compare
2779 : : * the comments at the head of heapam_visibility.c.
2780 : : *
2781 : : * Also, while our own xact won't be listed in the snapshot,
2782 : : * we need not check for TransactionIdIsCurrentTransactionId
2783 : : * because our transaction cannot (yet) have queued any
2784 : : * messages.
2785 : : */
2786 : 0 : *current = thisentry;
2787 : 0 : reachedStop = true;
2788 : 0 : break;
2789 : : }
2790 : :
2791 : : /*
2792 : : * Quick check for the case that we're not listening on any
2793 : : * channels, before calling TransactionIdDidCommit(). This makes
2794 : : * that case a little faster, but more importantly, it ensures
2795 : : * that if there's a bad entry in the queue for which
2796 : : * TransactionIdDidCommit() fails for some reason, we can skip
2797 : : * over it on the first LISTEN in a session, and not get stuck on
2798 : : * it indefinitely. (This is a little trickier than it looks: it
2799 : : * works because BecomeRegisteredListener runs this code before we
2800 : : * have made the first entry in localChannelTable.)
2801 : : */
2802 [ + - + - ]: 4 : if (LocalChannelTableIsEmpty())
2803 : 4 : continue;
2804 : :
2805 [ # # ]: 0 : if (TransactionIdDidCommit(qe->xid))
2806 : : {
2807 : 0 : memcpy(local_buf_end, qe, qe->length);
2808 : 0 : local_buf_end += qe->length;
2809 : 0 : }
2810 : : else
2811 : : {
2812 : : /*
2813 : : * The source transaction aborted or crashed, so we just
2814 : : * ignore its notifications.
2815 : : */
2816 : : }
2817 : 0 : }
2818 : :
2819 : : /* Loop back if we're not at end of page */
2820 [ - + - + : 5 : } while (!reachedEndOfPage);
+ ]
2821 : :
2822 : : /* Release lock that we got from SimpleLruReadPage_ReadOnly() */
2823 : 1 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2824 : :
2825 : : /*
2826 : : * Now that we have let go of the SLRU bank lock, send the notifications
2827 : : * to our backend
2828 : : */
2829 [ + - ]: 1 : Assert(local_buf_end - local_buf <= BLCKSZ);
2830 [ - + ]: 1 : for (char *p = local_buf; p < local_buf_end;)
2831 : : {
2832 : 0 : AsyncQueueEntry *qe = (AsyncQueueEntry *) p;
2833 : :
2834 : : /* qe->data is the null-terminated channel name */
2835 : 0 : char *channel = qe->data;
2836 : :
2837 [ # # ]: 0 : if (IsListeningOn(channel))
2838 : : {
2839 : : /* payload follows channel name */
2840 : 0 : char *payload = qe->data + strlen(channel) + 1;
2841 : :
2842 : 0 : NotifyMyFrontEnd(channel, payload, qe->srcPid);
2843 : 0 : }
2844 : :
2845 : 0 : p += qe->length;
2846 : 0 : }
2847 : :
2848 [ + - - + ]: 1 : if (QUEUE_POS_EQUAL(*current, stop))
2849 : 1 : reachedStop = true;
2850 : :
2851 : 2 : return reachedStop;
2852 : 1 : }
2853 : :
2854 : : /*
2855 : : * Advance the shared queue tail variable to the minimum of all the
2856 : : * per-backend tail pointers. Truncate pg_notify space if possible.
2857 : : *
2858 : : * This is (usually) called during CommitTransaction(), so it's important for
2859 : : * it to have very low probability of failure.
2860 : : */
2861 : : static void
2862 : 1 : asyncQueueAdvanceTail(void)
2863 : : {
2864 : 1 : QueuePosition min;
2865 : 1 : int64 oldtailpage;
2866 : 1 : int64 newtailpage;
2867 : 1 : int64 boundary;
2868 : :
2869 : : /* Restrict task to one backend per cluster; see SimpleLruTruncate(). */
2870 : 1 : LWLockAcquire(NotifyQueueTailLock, LW_EXCLUSIVE);
2871 : :
2872 : : /*
2873 : : * Compute the new tail. Pre-v13, it's essential that QUEUE_TAIL be exact
2874 : : * (ie, exactly match at least one backend's queue position), so it must
2875 : : * be updated atomically with the actual computation. Since v13, we could
2876 : : * get away with not doing it like that, but it seems prudent to keep it
2877 : : * so.
2878 : : *
2879 : : * Also, because incoming backends will scan forward from QUEUE_TAIL, that
2880 : : * must be advanced before we can truncate any data. Thus, QUEUE_TAIL is
2881 : : * the logical tail, while QUEUE_STOP_PAGE is the physical tail, or oldest
2882 : : * un-truncated page. When QUEUE_STOP_PAGE != QUEUE_POS_PAGE(QUEUE_TAIL),
2883 : : * there are pages we can truncate but haven't yet finished doing so.
2884 : : *
2885 : : * For concurrency's sake, we don't want to hold NotifyQueueLock while
2886 : : * performing SimpleLruTruncate. This is OK because no backend will try
2887 : : * to access the pages we are in the midst of truncating.
2888 : : */
2889 : 1 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
2890 : 1 : min = QUEUE_HEAD;
2891 [ + - ]: 1 : for (ProcNumber i = QUEUE_FIRST_LISTENER; i != INVALID_PROC_NUMBER; i = QUEUE_NEXT_LISTENER(i))
2892 : : {
2893 [ # # ]: 0 : Assert(QUEUE_BACKEND_PID(i) != InvalidPid);
2894 [ # # # # : 0 : min = QUEUE_POS_MIN(min, QUEUE_BACKEND_POS(i));
# # ]
2895 : 0 : }
2896 : 1 : QUEUE_TAIL = min;
2897 : 1 : oldtailpage = QUEUE_STOP_PAGE;
2898 : 1 : LWLockRelease(NotifyQueueLock);
2899 : :
2900 : : /*
2901 : : * We can truncate something if the global tail advanced across an SLRU
2902 : : * segment boundary.
2903 : : *
2904 : : * XXX it might be better to truncate only once every several segments, to
2905 : : * reduce the number of directory scans.
2906 : : */
2907 : 1 : newtailpage = QUEUE_POS_PAGE(min);
2908 : 1 : boundary = newtailpage - (newtailpage % SLRU_PAGES_PER_SEGMENT);
2909 [ + - ]: 1 : if (asyncQueuePagePrecedes(oldtailpage, boundary))
2910 : : {
2911 : : /*
2912 : : * SimpleLruTruncate() will ask for SLRU bank locks but will also
2913 : : * release the lock again.
2914 : : */
2915 : 0 : SimpleLruTruncate(NotifyCtl, newtailpage);
2916 : :
2917 : 0 : LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);
2918 : 0 : QUEUE_STOP_PAGE = newtailpage;
2919 : 0 : LWLockRelease(NotifyQueueLock);
2920 : 0 : }
2921 : :
2922 : 1 : LWLockRelease(NotifyQueueTailLock);
2923 : 1 : }
2924 : :
2925 : : /*
2926 : : * AsyncNotifyFreezeXids
2927 : : *
2928 : : * Prepare the async notification queue for CLOG truncation by freezing
2929 : : * transaction IDs that are about to become inaccessible.
2930 : : *
2931 : : * This function is called by VACUUM before advancing datfrozenxid. It scans
2932 : : * the notification queue and replaces XIDs that would become inaccessible
2933 : : * after CLOG truncation with special markers:
2934 : : * - Committed transactions are set to FrozenTransactionId
2935 : : * - Aborted/crashed transactions are set to InvalidTransactionId
2936 : : *
2937 : : * Only XIDs < newFrozenXid are processed, as those are the ones whose CLOG
2938 : : * pages will be truncated. If XID < newFrozenXid, it cannot still be running
2939 : : * (or it would have held back newFrozenXid through ProcArray).
2940 : : * Therefore, if TransactionIdDidCommit returns false, we know the transaction
2941 : : * either aborted explicitly or crashed, and we can safely mark it invalid.
2942 : : */
2943 : : void
2944 : 2 : AsyncNotifyFreezeXids(TransactionId newFrozenXid)
2945 : : {
2946 : 2 : QueuePosition pos;
2947 : 2 : QueuePosition head;
2948 : 2 : int64 curpage = -1;
2949 : 2 : int slotno = -1;
2950 : 2 : char *page_buffer = NULL;
2951 : 2 : bool page_dirty = false;
2952 : :
2953 : : /*
2954 : : * Acquire locks in the correct order to avoid deadlocks. As per the
2955 : : * locking protocol: NotifyQueueTailLock, then NotifyQueueLock, then SLRU
2956 : : * bank locks.
2957 : : *
2958 : : * We only need SHARED mode since we're just reading the head/tail
2959 : : * positions, not modifying them.
2960 : : */
2961 : 2 : LWLockAcquire(NotifyQueueTailLock, LW_SHARED);
2962 : 2 : LWLockAcquire(NotifyQueueLock, LW_SHARED);
2963 : :
2964 : 2 : pos = QUEUE_TAIL;
2965 : 2 : head = QUEUE_HEAD;
2966 : :
2967 : : /* Release NotifyQueueLock early, we only needed to read the positions */
2968 : 2 : LWLockRelease(NotifyQueueLock);
2969 : :
2970 : : /*
2971 : : * Scan the queue from tail to head, freezing XIDs as needed. We hold
2972 : : * NotifyQueueTailLock throughout to ensure the tail doesn't move while
2973 : : * we're working.
2974 : : */
2975 [ - + + - ]: 2 : while (!QUEUE_POS_EQUAL(pos, head))
2976 : : {
2977 : 0 : AsyncQueueEntry *qe;
2978 : 0 : TransactionId xid;
2979 : 0 : int64 pageno = QUEUE_POS_PAGE(pos);
2980 : 0 : int offset = QUEUE_POS_OFFSET(pos);
2981 : :
2982 : : /* If we need a different page, release old lock and get new one */
2983 [ # # ]: 0 : if (pageno != curpage)
2984 : : {
2985 : 0 : LWLock *lock;
2986 : :
2987 : : /* Release previous page if any */
2988 [ # # ]: 0 : if (slotno >= 0)
2989 : : {
2990 [ # # ]: 0 : if (page_dirty)
2991 : : {
2992 : 0 : NotifyCtl->shared->page_dirty[slotno] = true;
2993 : 0 : page_dirty = false;
2994 : 0 : }
2995 : 0 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
2996 : 0 : }
2997 : :
2998 : 0 : lock = SimpleLruGetBankLock(NotifyCtl, pageno);
2999 : 0 : LWLockAcquire(lock, LW_EXCLUSIVE);
3000 : 0 : slotno = SimpleLruReadPage(NotifyCtl, pageno, true,
3001 : : InvalidTransactionId);
3002 : 0 : page_buffer = NotifyCtl->shared->page_buffer[slotno];
3003 : 0 : curpage = pageno;
3004 : 0 : }
3005 : :
3006 : 0 : qe = (AsyncQueueEntry *) (page_buffer + offset);
3007 : 0 : xid = qe->xid;
3008 : :
3009 [ # # # # ]: 0 : if (TransactionIdIsNormal(xid) &&
3010 : 0 : TransactionIdPrecedes(xid, newFrozenXid))
3011 : : {
3012 [ # # ]: 0 : if (TransactionIdDidCommit(xid))
3013 : : {
3014 : 0 : qe->xid = FrozenTransactionId;
3015 : 0 : page_dirty = true;
3016 : 0 : }
3017 : : else
3018 : : {
3019 : 0 : qe->xid = InvalidTransactionId;
3020 : 0 : page_dirty = true;
3021 : : }
3022 : 0 : }
3023 : :
3024 : : /* Advance to next entry */
3025 : 0 : asyncQueueAdvance(&pos, qe->length);
3026 : 0 : }
3027 : :
3028 : : /* Release final page lock if we acquired one */
3029 [ + - ]: 2 : if (slotno >= 0)
3030 : : {
3031 [ # # ]: 0 : if (page_dirty)
3032 : 0 : NotifyCtl->shared->page_dirty[slotno] = true;
3033 : 0 : LWLockRelease(SimpleLruGetBankLock(NotifyCtl, curpage));
3034 : 0 : }
3035 : :
3036 : 2 : LWLockRelease(NotifyQueueTailLock);
3037 : 2 : }
3038 : :
3039 : : /*
3040 : : * ProcessIncomingNotify
3041 : : *
3042 : : * Scan the queue for arriving notifications and report them to the front
3043 : : * end. The notifications might be from other sessions, or our own;
3044 : : * there's no need to distinguish here.
3045 : : *
3046 : : * If "flush" is true, force any frontend messages out immediately.
3047 : : *
3048 : : * NOTE: since we are outside any transaction, we must create our own.
3049 : : */
3050 : : static void
3051 : 0 : ProcessIncomingNotify(bool flush)
3052 : : {
3053 : : /* We *must* reset the flag */
3054 : 0 : notifyInterruptPending = false;
3055 : :
3056 : : /* Do nothing else if we aren't actively listening */
3057 [ # # # # ]: 0 : if (LocalChannelTableIsEmpty())
3058 : 0 : return;
3059 : :
3060 [ # # ]: 0 : if (Trace_notify)
3061 [ # # # # ]: 0 : elog(DEBUG1, "ProcessIncomingNotify");
3062 : :
3063 : 0 : set_ps_display("notify interrupt");
3064 : :
3065 : : /*
3066 : : * We must run asyncQueueReadAllNotifications inside a transaction, else
3067 : : * bad things happen if it gets an error.
3068 : : */
3069 : 0 : StartTransactionCommand();
3070 : :
3071 : 0 : asyncQueueReadAllNotifications();
3072 : :
3073 : 0 : CommitTransactionCommand();
3074 : :
3075 : : /*
3076 : : * If this isn't an end-of-command case, we must flush the notify messages
3077 : : * to ensure frontend gets them promptly.
3078 : : */
3079 [ # # ]: 0 : if (flush)
3080 : 0 : pq_flush();
3081 : :
3082 : 0 : set_ps_display("idle");
3083 : :
3084 [ # # ]: 0 : if (Trace_notify)
3085 [ # # # # ]: 0 : elog(DEBUG1, "ProcessIncomingNotify: done");
3086 : 0 : }
3087 : :
3088 : : /*
3089 : : * Send NOTIFY message to my front end.
3090 : : */
3091 : : void
3092 : 0 : NotifyMyFrontEnd(const char *channel, const char *payload, int32 srcPid)
3093 : : {
3094 [ # # ]: 0 : if (whereToSendOutput == DestRemote)
3095 : : {
3096 : 0 : StringInfoData buf;
3097 : :
3098 : 0 : pq_beginmessage(&buf, PqMsg_NotificationResponse);
3099 : 0 : pq_sendint32(&buf, srcPid);
3100 : 0 : pq_sendstring(&buf, channel);
3101 : 0 : pq_sendstring(&buf, payload);
3102 : 0 : pq_endmessage(&buf);
3103 : :
3104 : : /*
3105 : : * NOTE: we do not do pq_flush() here. Some level of caller will
3106 : : * handle it later, allowing this message to be combined into a packet
3107 : : * with other ones.
3108 : : */
3109 : 0 : }
3110 : : else
3111 [ # # # # ]: 0 : elog(INFO, "NOTIFY for \"%s\" payload \"%s\"", channel, payload);
3112 : 0 : }
3113 : :
3114 : : /* Does pendingNotifies include a match for the given event? */
3115 : : static bool
3116 : 0 : AsyncExistsPendingNotify(Notification *n)
3117 : : {
3118 [ # # ]: 0 : if (pendingNotifies == NULL)
3119 : 0 : return false;
3120 : :
3121 [ # # ]: 0 : if (pendingNotifies->hashtab != NULL)
3122 : : {
3123 : : /* Use the hash table to probe for a match */
3124 [ # # ]: 0 : if (hash_search(pendingNotifies->hashtab,
3125 : : &n,
3126 : : HASH_FIND,
3127 : : NULL))
3128 : 0 : return true;
3129 : 0 : }
3130 : : else
3131 : : {
3132 : : /* Must scan the event list */
3133 : 0 : ListCell *l;
3134 : :
3135 [ # # # # : 0 : foreach(l, pendingNotifies->events)
# # # # ]
3136 : : {
3137 : 0 : Notification *oldn = (Notification *) lfirst(l);
3138 : :
3139 [ # # ]: 0 : if (n->channel_len == oldn->channel_len &&
3140 [ # # # # ]: 0 : n->payload_len == oldn->payload_len &&
3141 : 0 : memcmp(n->data, oldn->data,
3142 : 0 : n->channel_len + n->payload_len + 2) == 0)
3143 : 0 : return true;
3144 [ # # ]: 0 : }
3145 [ # # # ]: 0 : }
3146 : :
3147 : 0 : return false;
3148 : 0 : }
3149 : :
3150 : : /*
3151 : : * Add a notification event to a pre-existing pendingNotifies list.
3152 : : *
3153 : : * Because pendingNotifies->events is already nonempty, this works
3154 : : * correctly no matter what CurrentMemoryContext is.
3155 : : */
3156 : : static void
3157 : 0 : AddEventToPendingNotifies(Notification *n)
3158 : : {
3159 [ # # ]: 0 : Assert(pendingNotifies->events != NIL);
3160 : :
3161 : : /* Create the hash tables if it's time to */
3162 [ # # # # ]: 0 : if (list_length(pendingNotifies->events) >= MIN_HASHABLE_NOTIFIES &&
3163 : 0 : pendingNotifies->hashtab == NULL)
3164 : : {
3165 : 0 : HASHCTL hash_ctl;
3166 : 0 : ListCell *l;
3167 : :
3168 : : /* Create the hash table */
3169 : 0 : hash_ctl.keysize = sizeof(Notification *);
3170 : 0 : hash_ctl.entrysize = sizeof(struct NotificationHash);
3171 : 0 : hash_ctl.hash = notification_hash;
3172 : 0 : hash_ctl.match = notification_match;
3173 : 0 : hash_ctl.hcxt = CurTransactionContext;
3174 : 0 : pendingNotifies->hashtab =
3175 : 0 : hash_create("Pending Notifies",
3176 : : 256L,
3177 : : &hash_ctl,
3178 : : HASH_ELEM | HASH_FUNCTION | HASH_COMPARE | HASH_CONTEXT);
3179 : :
3180 : : /* Create the unique channel name table */
3181 [ # # ]: 0 : Assert(pendingNotifies->uniqueChannelHash == NULL);
3182 : 0 : hash_ctl.keysize = NAMEDATALEN;
3183 : 0 : hash_ctl.entrysize = sizeof(ChannelName);
3184 : 0 : hash_ctl.hcxt = CurTransactionContext;
3185 : 0 : pendingNotifies->uniqueChannelHash =
3186 : 0 : hash_create("Pending Notify Channel Names",
3187 : : 64L,
3188 : : &hash_ctl,
3189 : : HASH_ELEM | HASH_STRINGS | HASH_CONTEXT);
3190 : :
3191 : : /* Insert all the already-existing events */
3192 [ # # # # : 0 : foreach(l, pendingNotifies->events)
# # ]
3193 : : {
3194 : 0 : Notification *oldn = (Notification *) lfirst(l);
3195 : 0 : char *channel = oldn->data;
3196 : 0 : bool found;
3197 : :
3198 : 0 : (void) hash_search(pendingNotifies->hashtab,
3199 : : &oldn,
3200 : : HASH_ENTER,
3201 : : &found);
3202 [ # # ]: 0 : Assert(!found);
3203 : :
3204 : : /* Add channel name to uniqueChannelHash; might be there already */
3205 : 0 : (void) hash_search(pendingNotifies->uniqueChannelHash,
3206 : 0 : channel,
3207 : : HASH_ENTER,
3208 : : NULL);
3209 : 0 : }
3210 : 0 : }
3211 : :
3212 : : /* Add new event to the list, in order */
3213 : 0 : pendingNotifies->events = lappend(pendingNotifies->events, n);
3214 : :
3215 : : /* Add event to the hash tables if needed */
3216 [ # # ]: 0 : if (pendingNotifies->hashtab != NULL)
3217 : : {
3218 : 0 : char *channel = n->data;
3219 : 0 : bool found;
3220 : :
3221 : 0 : (void) hash_search(pendingNotifies->hashtab,
3222 : : &n,
3223 : : HASH_ENTER,
3224 : : &found);
3225 [ # # ]: 0 : Assert(!found);
3226 : :
3227 : : /* Add channel name to uniqueChannelHash; might be there already */
3228 : 0 : (void) hash_search(pendingNotifies->uniqueChannelHash,
3229 : 0 : channel,
3230 : : HASH_ENTER,
3231 : : NULL);
3232 : 0 : }
3233 : 0 : }
3234 : :
3235 : : /*
3236 : : * notification_hash: hash function for notification hash table
3237 : : *
3238 : : * The hash "keys" are pointers to Notification structs.
3239 : : */
3240 : : static uint32
3241 : 0 : notification_hash(const void *key, Size keysize)
3242 : : {
3243 : 0 : const Notification *k = *(const Notification *const *) key;
3244 : :
3245 [ # # ]: 0 : Assert(keysize == sizeof(Notification *));
3246 : : /* We don't bother to include the payload's trailing null in the hash */
3247 : 0 : return DatumGetUInt32(hash_any((const unsigned char *) k->data,
3248 : 0 : k->channel_len + k->payload_len + 1));
3249 : 0 : }
3250 : :
3251 : : /*
3252 : : * notification_match: match function to use with notification_hash
3253 : : */
3254 : : static int
3255 : 0 : notification_match(const void *key1, const void *key2, Size keysize)
3256 : : {
3257 : 0 : const Notification *k1 = *(const Notification *const *) key1;
3258 : 0 : const Notification *k2 = *(const Notification *const *) key2;
3259 : :
3260 [ # # ]: 0 : Assert(keysize == sizeof(Notification *));
3261 [ # # ]: 0 : if (k1->channel_len == k2->channel_len &&
3262 [ # # # # ]: 0 : k1->payload_len == k2->payload_len &&
3263 : 0 : memcmp(k1->data, k2->data,
3264 : 0 : k1->channel_len + k1->payload_len + 2) == 0)
3265 : 0 : return 0; /* equal */
3266 : 0 : return 1; /* not equal */
3267 : 0 : }
3268 : :
3269 : : /* Clear the pendingActions and pendingNotifies lists. */
3270 : : static void
3271 : 7025 : ClearPendingActionsAndNotifies(void)
3272 : : {
3273 : : /*
3274 : : * Everything's allocated in either TopTransactionContext or the context
3275 : : * for the subtransaction to which it corresponds. So, there's nothing to
3276 : : * do here except reset the pointers; the space will be reclaimed when the
3277 : : * contexts are deleted.
3278 : : */
3279 : 7025 : pendingActions = NULL;
3280 : 7025 : pendingNotifies = NULL;
3281 : : /* Also clear pendingListenActions, which is derived from pendingActions */
3282 : 7025 : pendingListenActions = NULL;
3283 : 7025 : }
3284 : :
3285 : : /*
3286 : : * GUC check_hook for notify_buffers
3287 : : */
3288 : : bool
3289 : 6 : check_notify_buffers(int *newval, void **extra, GucSource source)
3290 : : {
3291 : 6 : return check_slru_buffers("notify_buffers", newval);
3292 : : }
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