Line data Source code
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 47812 : proc_exit(int code)
106 : {
107 : /* not safe if forked by system(), etc. */
108 47812 : 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 47812 : 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 47812 : elog(DEBUG3, "exit(%d)", code);
156 :
157 47812 : 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 95556 : 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 95556 : 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 95556 : InterruptPending = false;
180 95556 : ProcDiePending = false;
181 95556 : QueryCancelPending = false;
182 95556 : InterruptHoldoffCount = 1;
183 95556 : 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 95556 : error_context_stack = NULL;
195 : /* For the same reason, reset debug_query_string before it's clobbered */
196 95556 : debug_query_string = NULL;
197 :
198 : /* do our shared memory exits first */
199 95556 : shmem_exit(code);
200 :
201 95556 : 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 173058 : while (--on_proc_exit_index >= 0)
214 77502 : on_proc_exit_list[on_proc_exit_index].function(code,
215 : on_proc_exit_list[on_proc_exit_index].arg);
216 :
217 95556 : on_proc_exit_index = 0;
218 95556 : }
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 95566 : shmem_exit(int code)
230 : {
231 95566 : 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 95566 : 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 95566 : elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
248 : code, before_shmem_exit_index);
249 325026 : while (--before_shmem_exit_index >= 0)
250 229460 : before_shmem_exit_list[before_shmem_exit_index].function(code,
251 : before_shmem_exit_list[before_shmem_exit_index].arg);
252 95566 : 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 95566 : 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 95566 : elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
281 : code, on_shmem_exit_index);
282 425790 : while (--on_shmem_exit_index >= 0)
283 330224 : on_shmem_exit_list[on_shmem_exit_index].function(code,
284 : on_shmem_exit_list[on_shmem_exit_index].arg);
285 95566 : on_shmem_exit_index = 0;
286 :
287 95566 : shmem_exit_inprogress = false;
288 95566 : }
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 47744 : 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 47744 : proc_exit_prepare(-1);
306 47744 : }
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 77502 : on_proc_exit(pg_on_exit_callback function, Datum arg)
317 : {
318 77502 : 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 77502 : on_proc_exit_list[on_proc_exit_index].function = function;
324 77502 : on_proc_exit_list[on_proc_exit_index].arg = arg;
325 :
326 77502 : ++on_proc_exit_index;
327 :
328 77502 : if (!atexit_callback_setup)
329 : {
330 2286 : atexit(atexit_callback);
331 2286 : atexit_callback_setup = true;
332 : }
333 77502 : }
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 234158 : before_shmem_exit(pg_on_exit_callback function, Datum arg)
345 : {
346 234158 : 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 234158 : before_shmem_exit_list[before_shmem_exit_index].function = function;
352 234158 : before_shmem_exit_list[before_shmem_exit_index].arg = arg;
353 :
354 234158 : ++before_shmem_exit_index;
355 :
356 234158 : if (!atexit_callback_setup)
357 : {
358 0 : atexit(atexit_callback);
359 0 : atexit_callback_setup = true;
360 : }
361 234158 : }
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 330224 : on_shmem_exit(pg_on_exit_callback function, Datum arg)
373 : {
374 330224 : 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 330224 : on_shmem_exit_list[on_shmem_exit_index].function = function;
380 330224 : on_shmem_exit_list[on_shmem_exit_index].arg = arg;
381 :
382 330224 : ++on_shmem_exit_index;
383 :
384 330224 : if (!atexit_callback_setup)
385 : {
386 0 : atexit(atexit_callback);
387 0 : atexit_callback_setup = true;
388 : }
389 330224 : }
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 4698 : cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
402 : {
403 4698 : if (before_shmem_exit_index > 0 &&
404 4698 : before_shmem_exit_list[before_shmem_exit_index - 1].function
405 4698 : == function &&
406 4698 : before_shmem_exit_list[before_shmem_exit_index - 1].arg == arg)
407 4698 : --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 4698 : }
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 45458 : on_exit_reset(void)
424 : {
425 45458 : before_shmem_exit_index = 0;
426 45458 : on_shmem_exit_index = 0;
427 45458 : on_proc_exit_index = 0;
428 45458 : reset_on_dsm_detach();
429 45458 : }
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 27500 : check_on_shmem_exit_lists_are_empty(void)
440 : {
441 27500 : if (before_shmem_exit_index)
442 0 : elog(FATAL, "before_shmem_exit has been called prematurely");
443 27500 : 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 27500 : }
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