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1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * ipc.c
4 : : * POSTGRES inter-process communication definitions.
5 : : *
6 : : * This file is misnamed, as it no longer has much of anything directly
7 : : * to do with IPC. The functionality here is concerned with managing
8 : : * exit-time cleanup for either a postmaster or a backend.
9 : : *
10 : : *
11 : : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
12 : : * Portions Copyright (c) 1994, Regents of the University of California
13 : : *
14 : : *
15 : : * IDENTIFICATION
16 : : * src/backend/storage/ipc/ipc.c
17 : : *
18 : : *-------------------------------------------------------------------------
19 : : */
20 : : #include "postgres.h"
21 : :
22 : : #include <signal.h>
23 : : #include <unistd.h>
24 : : #include <sys/stat.h>
25 : :
26 : : #include "miscadmin.h"
27 : : #ifdef PROFILE_PID_DIR
28 : : #include "postmaster/autovacuum.h"
29 : : #endif
30 : : #include "storage/dsm.h"
31 : : #include "storage/ipc.h"
32 : : #include "storage/lwlock.h"
33 : : #include "tcop/tcopprot.h"
34 : :
35 : :
36 : : /*
37 : : * This flag is set during proc_exit() to change ereport()'s behavior,
38 : : * so that an ereport() from an on_proc_exit routine cannot get us out
39 : : * of the exit procedure. We do NOT want to go back to the idle loop...
40 : : */
41 : : bool proc_exit_inprogress = false;
42 : :
43 : : /*
44 : : * Set when shmem_exit() is in progress.
45 : : */
46 : : bool shmem_exit_inprogress = false;
47 : :
48 : : /*
49 : : * This flag tracks whether we've called atexit() in the current process
50 : : * (or in the parent postmaster).
51 : : */
52 : : static bool atexit_callback_setup = false;
53 : :
54 : : /* local functions */
55 : : static void proc_exit_prepare(int code);
56 : :
57 : :
58 : : /* ----------------------------------------------------------------
59 : : * exit() handling stuff
60 : : *
61 : : * These functions are in generally the same spirit as atexit(),
62 : : * but provide some additional features we need --- in particular,
63 : : * we want to register callbacks to invoke when we are disconnecting
64 : : * from a broken shared-memory context but not exiting the postmaster.
65 : : *
66 : : * Callback functions can take zero, one, or two args: the first passed
67 : : * arg is the integer exitcode, the second is the Datum supplied when
68 : : * the callback was registered.
69 : : * ----------------------------------------------------------------
70 : : */
71 : :
72 : : #define MAX_ON_EXITS 20
73 : :
74 : : struct ONEXIT
75 : : {
76 : : pg_on_exit_callback function;
77 : : Datum arg;
78 : : };
79 : :
80 : : static struct ONEXIT on_proc_exit_list[MAX_ON_EXITS];
81 : : static struct ONEXIT on_shmem_exit_list[MAX_ON_EXITS];
82 : : static struct ONEXIT before_shmem_exit_list[MAX_ON_EXITS];
83 : :
84 : : static int on_proc_exit_index,
85 : : on_shmem_exit_index,
86 : : before_shmem_exit_index;
87 : :
88 : :
89 : : /* ----------------------------------------------------------------
90 : : * proc_exit
91 : : *
92 : : * this function calls all the callbacks registered
93 : : * for it (to free resources) and then calls exit.
94 : : *
95 : : * This should be the only function to call exit().
96 : : * -cim 2/6/90
97 : : *
98 : : * Unfortunately, we can't really guarantee that add-on code
99 : : * obeys the rule of not calling exit() directly. So, while
100 : : * this is the preferred way out of the system, we also register
101 : : * an atexit callback that will make sure cleanup happens.
102 : : * ----------------------------------------------------------------
103 : : */
104 : : void
105 : 810 : proc_exit(int code)
106 : : {
107 : : /* not safe if forked by system(), etc. */
108 [ + - ]: 810 : if (MyProcPid != (int) getpid())
109 [ # # # # ]: 0 : elog(PANIC, "proc_exit() called in child process");
110 : :
111 : : /* Clean up everything that must be cleaned up */
112 : 810 : proc_exit_prepare(code);
113 : :
114 : : #ifdef PROFILE_PID_DIR
115 : : {
116 : : /*
117 : : * If we are profiling ourself then gprof's mcleanup() is about to
118 : : * write out a profile to ./gmon.out. Since mcleanup() always uses a
119 : : * fixed file name, each backend will overwrite earlier profiles. To
120 : : * fix that, we create a separate subdirectory for each backend
121 : : * (./gprof/pid) and 'cd' to that subdirectory before we exit() - that
122 : : * forces mcleanup() to write each profile into its own directory. We
123 : : * end up with something like: $PGDATA/gprof/8829/gmon.out
124 : : * $PGDATA/gprof/8845/gmon.out ...
125 : : *
126 : : * To avoid undesirable disk space bloat, autovacuum workers are
127 : : * discriminated against: all their gmon.out files go into the same
128 : : * subdirectory. Without this, an installation that is "just sitting
129 : : * there" nonetheless eats megabytes of disk space every few seconds.
130 : : *
131 : : * Note that we do this here instead of in an on_proc_exit() callback
132 : : * because we want to ensure that this code executes last - we don't
133 : : * want to interfere with any other on_proc_exit() callback. For the
134 : : * same reason, we do not include it in proc_exit_prepare ... so if
135 : : * you are exiting in the "wrong way" you won't drop your profile in a
136 : : * nice place.
137 : : */
138 : : char gprofDirName[32];
139 : :
140 : : if (AmAutoVacuumWorkerProcess())
141 : : snprintf(gprofDirName, 32, "gprof/avworker");
142 : : else
143 : : snprintf(gprofDirName, 32, "gprof/%d", (int) getpid());
144 : :
145 : : /*
146 : : * Use mkdir() instead of MakePGDirectory() since we aren't making a
147 : : * PG directory here.
148 : : */
149 : : mkdir("gprof", S_IRWXU | S_IRWXG | S_IRWXO);
150 : : mkdir(gprofDirName, S_IRWXU | S_IRWXG | S_IRWXO);
151 : : chdir(gprofDirName);
152 : : }
153 : : #endif
154 : :
155 [ - + + + ]: 810 : elog(DEBUG3, "exit(%d)", code);
156 : :
157 : 810 : exit(code);
158 : : }
159 : :
160 : : /*
161 : : * Code shared between proc_exit and the atexit handler. Note that in
162 : : * normal exit through proc_exit, this will actually be called twice ...
163 : : * but the second call will have nothing to do.
164 : : */
165 : : static void
166 : 1620 : proc_exit_prepare(int code)
167 : : {
168 : : /*
169 : : * Once we set this flag, we are committed to exit. Any ereport() will
170 : : * NOT send control back to the main loop, but right back here.
171 : : */
172 : 1620 : proc_exit_inprogress = true;
173 : :
174 : : /*
175 : : * Forget any pending cancel or die requests; we're doing our best to
176 : : * close up shop already. Note that the signal handlers will not set
177 : : * these flags again, now that proc_exit_inprogress is set.
178 : : */
179 : 1620 : InterruptPending = false;
180 : 1620 : ProcDiePending = false;
181 : 1620 : QueryCancelPending = false;
182 : 1620 : InterruptHoldoffCount = 1;
183 : 1620 : CritSectionCount = 0;
184 : :
185 : : /*
186 : : * Also clear the error context stack, to prevent error callbacks from
187 : : * being invoked by any elog/ereport calls made during proc_exit. Whatever
188 : : * context they might want to offer is probably not relevant, and in any
189 : : * case they are likely to fail outright after we've done things like
190 : : * aborting any open transaction. (In normal exit scenarios the context
191 : : * stack should be empty anyway, but it might not be in the case of
192 : : * elog(FATAL) for example.)
193 : : */
194 : 1620 : error_context_stack = NULL;
195 : : /* For the same reason, reset debug_query_string before it's clobbered */
196 : 1620 : debug_query_string = NULL;
197 : :
198 : : /* do our shared memory exits first */
199 : 1620 : shmem_exit(code);
200 : :
201 [ - + - + ]: 1620 : elog(DEBUG3, "proc_exit(%d): %d callbacks to make",
202 : : code, on_proc_exit_index);
203 : :
204 : : /*
205 : : * call all the registered callbacks.
206 : : *
207 : : * Note that since we decrement on_proc_exit_index each time, if a
208 : : * callback calls ereport(ERROR) or ereport(FATAL) then it won't be
209 : : * invoked again when control comes back here (nor will the
210 : : * previously-completed callbacks). So, an infinite loop should not be
211 : : * possible.
212 : : */
213 [ + + ]: 2749 : while (--on_proc_exit_index >= 0)
214 : 2258 : on_proc_exit_list[on_proc_exit_index].function(code,
215 : 1129 : on_proc_exit_list[on_proc_exit_index].arg);
216 : :
217 : 1620 : on_proc_exit_index = 0;
218 : 1620 : }
219 : :
220 : : /* ------------------
221 : : * Run all of the on_shmem_exit routines --- but don't actually exit.
222 : : * This is used by the postmaster to re-initialize shared memory and
223 : : * semaphores after a backend dies horribly. As with proc_exit(), we
224 : : * remove each callback from the list before calling it, to avoid
225 : : * infinite loop in case of error.
226 : : * ------------------
227 : : */
228 : : void
229 : 1620 : shmem_exit(int code)
230 : : {
231 : 1620 : shmem_exit_inprogress = true;
232 : :
233 : : /*
234 : : * Release any LWLocks we might be holding before callbacks run. This
235 : : * prevents accessing locks in detached DSM segments and allows callbacks
236 : : * to acquire new locks.
237 : : */
238 : 1620 : LWLockReleaseAll();
239 : :
240 : : /*
241 : : * Call before_shmem_exit callbacks.
242 : : *
243 : : * These should be things that need most of the system to still be up and
244 : : * working, such as cleanup of temp relations, which requires catalog
245 : : * access.
246 : : */
247 [ - + - + ]: 1620 : elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
248 : : code, before_shmem_exit_index);
249 [ + + ]: 6226 : while (--before_shmem_exit_index >= 0)
250 : 9212 : before_shmem_exit_list[before_shmem_exit_index].function(code,
251 : 4606 : before_shmem_exit_list[before_shmem_exit_index].arg);
252 : 1620 : before_shmem_exit_index = 0;
253 : :
254 : : /*
255 : : * Call dynamic shared memory callbacks.
256 : : *
257 : : * These serve the same purpose as late callbacks, but for dynamic shared
258 : : * memory segments rather than the main shared memory segment.
259 : : * dsm_backend_shutdown() has the same kind of progressive logic we use
260 : : * for the main shared memory segment; namely, it unregisters each
261 : : * callback before invoking it, so that we don't get stuck in an infinite
262 : : * loop if one of those callbacks itself throws an ERROR or FATAL.
263 : : *
264 : : * Note that explicitly calling this function here is quite different from
265 : : * registering it as an on_shmem_exit callback for precisely this reason:
266 : : * if one dynamic shared memory callback errors out, the remaining
267 : : * callbacks will still be invoked. Thus, hard-coding this call puts it
268 : : * equal footing with callbacks for the main shared memory segment.
269 : : */
270 : 1620 : dsm_backend_shutdown();
271 : :
272 : : /*
273 : : * Call on_shmem_exit callbacks.
274 : : *
275 : : * These are generally releasing low-level shared memory resources. In
276 : : * some cases, this is a backstop against the possibility that the early
277 : : * callbacks might themselves fail, leading to re-entry to this routine;
278 : : * in other cases, it's cleanup that only happens at process exit.
279 : : */
280 [ - + - + ]: 1620 : elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
281 : : code, on_shmem_exit_index);
282 [ + + ]: 7290 : while (--on_shmem_exit_index >= 0)
283 : 11340 : on_shmem_exit_list[on_shmem_exit_index].function(code,
284 : 5670 : on_shmem_exit_list[on_shmem_exit_index].arg);
285 : 1620 : on_shmem_exit_index = 0;
286 : :
287 : 1620 : shmem_exit_inprogress = false;
288 : 1620 : }
289 : :
290 : : /* ----------------------------------------------------------------
291 : : * atexit_callback
292 : : *
293 : : * Backstop to ensure that direct calls of exit() don't mess us up.
294 : : *
295 : : * Somebody who was being really uncooperative could call _exit(),
296 : : * but for that case we have a "dead man switch" that will make the
297 : : * postmaster treat it as a crash --- see pmsignal.c.
298 : : * ----------------------------------------------------------------
299 : : */
300 : : static void
301 : 810 : atexit_callback(void)
302 : : {
303 : : /* Clean up everything that must be cleaned up */
304 : : /* ... too bad we don't know the real exit code ... */
305 : 810 : proc_exit_prepare(-1);
306 : 810 : }
307 : :
308 : : /* ----------------------------------------------------------------
309 : : * on_proc_exit
310 : : *
311 : : * this function adds a callback function to the list of
312 : : * functions invoked by proc_exit(). -cim 2/6/90
313 : : * ----------------------------------------------------------------
314 : : */
315 : : void
316 : 1129 : on_proc_exit(pg_on_exit_callback function, Datum arg)
317 : : {
318 [ + - ]: 1129 : if (on_proc_exit_index >= MAX_ON_EXITS)
319 [ # # # # ]: 0 : ereport(FATAL,
320 : : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
321 : : errmsg_internal("out of on_proc_exit slots")));
322 : :
323 : 1129 : on_proc_exit_list[on_proc_exit_index].function = function;
324 : 1129 : on_proc_exit_list[on_proc_exit_index].arg = arg;
325 : :
326 : 1129 : ++on_proc_exit_index;
327 : :
328 [ + + ]: 1129 : if (!atexit_callback_setup)
329 : : {
330 : 6 : atexit(atexit_callback);
331 : 6 : atexit_callback_setup = true;
332 : 6 : }
333 : 1129 : }
334 : :
335 : : /* ----------------------------------------------------------------
336 : : * before_shmem_exit
337 : : *
338 : : * Register early callback to perform user-level cleanup,
339 : : * e.g. transaction abort, before we begin shutting down
340 : : * low-level subsystems.
341 : : * ----------------------------------------------------------------
342 : : */
343 : : void
344 : 4782 : before_shmem_exit(pg_on_exit_callback function, Datum arg)
345 : : {
346 [ + - ]: 4782 : if (before_shmem_exit_index >= MAX_ON_EXITS)
347 [ # # # # ]: 0 : ereport(FATAL,
348 : : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
349 : : errmsg_internal("out of before_shmem_exit slots")));
350 : :
351 : 4782 : before_shmem_exit_list[before_shmem_exit_index].function = function;
352 : 4782 : before_shmem_exit_list[before_shmem_exit_index].arg = arg;
353 : :
354 : 4782 : ++before_shmem_exit_index;
355 : :
356 [ + - ]: 4782 : if (!atexit_callback_setup)
357 : : {
358 : 0 : atexit(atexit_callback);
359 : 0 : atexit_callback_setup = true;
360 : 0 : }
361 : 4782 : }
362 : :
363 : : /* ----------------------------------------------------------------
364 : : * on_shmem_exit
365 : : *
366 : : * Register ordinary callback to perform low-level shutdown
367 : : * (e.g. releasing our PGPROC); run after before_shmem_exit
368 : : * callbacks and before on_proc_exit callbacks.
369 : : * ----------------------------------------------------------------
370 : : */
371 : : void
372 : 5670 : on_shmem_exit(pg_on_exit_callback function, Datum arg)
373 : : {
374 [ + - ]: 5670 : if (on_shmem_exit_index >= MAX_ON_EXITS)
375 [ # # # # ]: 0 : ereport(FATAL,
376 : : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
377 : : errmsg_internal("out of on_shmem_exit slots")));
378 : :
379 : 5670 : on_shmem_exit_list[on_shmem_exit_index].function = function;
380 : 5670 : on_shmem_exit_list[on_shmem_exit_index].arg = arg;
381 : :
382 : 5670 : ++on_shmem_exit_index;
383 : :
384 [ + - ]: 5670 : if (!atexit_callback_setup)
385 : : {
386 : 0 : atexit(atexit_callback);
387 : 0 : atexit_callback_setup = true;
388 : 0 : }
389 : 5670 : }
390 : :
391 : : /* ----------------------------------------------------------------
392 : : * cancel_before_shmem_exit
393 : : *
394 : : * this function removes a previously-registered before_shmem_exit
395 : : * callback. We only look at the latest entry for removal, as we
396 : : * expect callers to add and remove temporary before_shmem_exit
397 : : * callbacks in strict LIFO order.
398 : : * ----------------------------------------------------------------
399 : : */
400 : : void
401 : 176 : cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
402 : : {
403 [ + - ]: 176 : if (before_shmem_exit_index > 0 &&
404 : 176 : before_shmem_exit_list[before_shmem_exit_index - 1].function
405 : 176 : == function &&
406 : 176 : before_shmem_exit_list[before_shmem_exit_index - 1].arg == arg)
407 : 176 : --before_shmem_exit_index;
408 : : else
409 [ # # # # ]: 0 : elog(ERROR, "before_shmem_exit callback (%p,0x%" PRIx64 ") is not the latest entry",
410 : : function, arg);
411 : 176 : }
412 : :
413 : : /* ----------------------------------------------------------------
414 : : * on_exit_reset
415 : : *
416 : : * this function clears all on_proc_exit() and on_shmem_exit()
417 : : * registered functions. This is used just after forking a backend,
418 : : * so that the backend doesn't believe it should call the postmaster's
419 : : * on-exit routines when it exits...
420 : : * ----------------------------------------------------------------
421 : : */
422 : : void
423 : 804 : on_exit_reset(void)
424 : : {
425 : 804 : before_shmem_exit_index = 0;
426 : 804 : on_shmem_exit_index = 0;
427 : 804 : on_proc_exit_index = 0;
428 : 804 : reset_on_dsm_detach();
429 : 804 : }
430 : :
431 : : /* ----------------------------------------------------------------
432 : : * check_on_shmem_exit_lists_are_empty
433 : : *
434 : : * Debugging check that no shmem cleanup handlers have been registered
435 : : * prematurely in the current process.
436 : : * ----------------------------------------------------------------
437 : : */
438 : : void
439 : 315 : check_on_shmem_exit_lists_are_empty(void)
440 : : {
441 [ + - ]: 315 : if (before_shmem_exit_index)
442 [ # # # # ]: 0 : elog(FATAL, "before_shmem_exit has been called prematurely");
443 [ + - ]: 315 : if (on_shmem_exit_index)
444 [ # # # # ]: 0 : elog(FATAL, "on_shmem_exit has been called prematurely");
445 : : /* Checking DSM detach state seems unnecessary given the above */
446 : 315 : }
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