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) 1996-2024, 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 "tcop/tcopprot.h"
33 :
34 :
35 : /*
36 : * This flag is set during proc_exit() to change ereport()'s behavior,
37 : * so that an ereport() from an on_proc_exit routine cannot get us out
38 : * of the exit procedure. We do NOT want to go back to the idle loop...
39 : */
40 : bool proc_exit_inprogress = false;
41 :
42 : /*
43 : * Set when shmem_exit() is in progress.
44 : */
45 : bool shmem_exit_inprogress = false;
46 :
47 : /*
48 : * This flag tracks whether we've called atexit() in the current process
49 : * (or in the parent postmaster).
50 : */
51 : static bool atexit_callback_setup = false;
52 :
53 : /* local functions */
54 : static void proc_exit_prepare(int code);
55 :
56 :
57 : /* ----------------------------------------------------------------
58 : * exit() handling stuff
59 : *
60 : * These functions are in generally the same spirit as atexit(),
61 : * but provide some additional features we need --- in particular,
62 : * we want to register callbacks to invoke when we are disconnecting
63 : * from a broken shared-memory context but not exiting the postmaster.
64 : *
65 : * Callback functions can take zero, one, or two args: the first passed
66 : * arg is the integer exitcode, the second is the Datum supplied when
67 : * the callback was registered.
68 : * ----------------------------------------------------------------
69 : */
70 :
71 : #define MAX_ON_EXITS 20
72 :
73 : struct ONEXIT
74 : {
75 : pg_on_exit_callback function;
76 : Datum arg;
77 : };
78 :
79 : static struct ONEXIT on_proc_exit_list[MAX_ON_EXITS];
80 : static struct ONEXIT on_shmem_exit_list[MAX_ON_EXITS];
81 : static struct ONEXIT before_shmem_exit_list[MAX_ON_EXITS];
82 :
83 : static int on_proc_exit_index,
84 : on_shmem_exit_index,
85 : before_shmem_exit_index;
86 :
87 :
88 : /* ----------------------------------------------------------------
89 : * proc_exit
90 : *
91 : * this function calls all the callbacks registered
92 : * for it (to free resources) and then calls exit.
93 : *
94 : * This should be the only function to call exit().
95 : * -cim 2/6/90
96 : *
97 : * Unfortunately, we can't really guarantee that add-on code
98 : * obeys the rule of not calling exit() directly. So, while
99 : * this is the preferred way out of the system, we also register
100 : * an atexit callback that will make sure cleanup happens.
101 : * ----------------------------------------------------------------
102 : */
103 : void
104 37672 : proc_exit(int code)
105 : {
106 : /* not safe if forked by system(), etc. */
107 37672 : if (MyProcPid != (int) getpid())
108 0 : elog(PANIC, "proc_exit() called in child process");
109 :
110 : /* Clean up everything that must be cleaned up */
111 37672 : proc_exit_prepare(code);
112 :
113 : #ifdef PROFILE_PID_DIR
114 : {
115 : /*
116 : * If we are profiling ourself then gprof's mcleanup() is about to
117 : * write out a profile to ./gmon.out. Since mcleanup() always uses a
118 : * fixed file name, each backend will overwrite earlier profiles. To
119 : * fix that, we create a separate subdirectory for each backend
120 : * (./gprof/pid) and 'cd' to that subdirectory before we exit() - that
121 : * forces mcleanup() to write each profile into its own directory. We
122 : * end up with something like: $PGDATA/gprof/8829/gmon.out
123 : * $PGDATA/gprof/8845/gmon.out ...
124 : *
125 : * To avoid undesirable disk space bloat, autovacuum workers are
126 : * discriminated against: all their gmon.out files go into the same
127 : * subdirectory. Without this, an installation that is "just sitting
128 : * there" nonetheless eats megabytes of disk space every few seconds.
129 : *
130 : * Note that we do this here instead of in an on_proc_exit() callback
131 : * because we want to ensure that this code executes last - we don't
132 : * want to interfere with any other on_proc_exit() callback. For the
133 : * same reason, we do not include it in proc_exit_prepare ... so if
134 : * you are exiting in the "wrong way" you won't drop your profile in a
135 : * nice place.
136 : */
137 : char gprofDirName[32];
138 :
139 : if (AmAutoVacuumWorkerProcess())
140 : snprintf(gprofDirName, 32, "gprof/avworker");
141 : else
142 : snprintf(gprofDirName, 32, "gprof/%d", (int) getpid());
143 :
144 : /*
145 : * Use mkdir() instead of MakePGDirectory() since we aren't making a
146 : * PG directory here.
147 : */
148 : mkdir("gprof", S_IRWXU | S_IRWXG | S_IRWXO);
149 : mkdir(gprofDirName, S_IRWXU | S_IRWXG | S_IRWXO);
150 : chdir(gprofDirName);
151 : }
152 : #endif
153 :
154 37672 : elog(DEBUG3, "exit(%d)", code);
155 :
156 37672 : exit(code);
157 : }
158 :
159 : /*
160 : * Code shared between proc_exit and the atexit handler. Note that in
161 : * normal exit through proc_exit, this will actually be called twice ...
162 : * but the second call will have nothing to do.
163 : */
164 : static void
165 75286 : proc_exit_prepare(int code)
166 : {
167 : /*
168 : * Once we set this flag, we are committed to exit. Any ereport() will
169 : * NOT send control back to the main loop, but right back here.
170 : */
171 75286 : proc_exit_inprogress = true;
172 :
173 : /*
174 : * Forget any pending cancel or die requests; we're doing our best to
175 : * close up shop already. Note that the signal handlers will not set
176 : * these flags again, now that proc_exit_inprogress is set.
177 : */
178 75286 : InterruptPending = false;
179 75286 : ProcDiePending = false;
180 75286 : QueryCancelPending = false;
181 75286 : InterruptHoldoffCount = 1;
182 75286 : CritSectionCount = 0;
183 :
184 : /*
185 : * Also clear the error context stack, to prevent error callbacks from
186 : * being invoked by any elog/ereport calls made during proc_exit. Whatever
187 : * context they might want to offer is probably not relevant, and in any
188 : * case they are likely to fail outright after we've done things like
189 : * aborting any open transaction. (In normal exit scenarios the context
190 : * stack should be empty anyway, but it might not be in the case of
191 : * elog(FATAL) for example.)
192 : */
193 75286 : error_context_stack = NULL;
194 : /* For the same reason, reset debug_query_string before it's clobbered */
195 75286 : debug_query_string = NULL;
196 :
197 : /* do our shared memory exits first */
198 75286 : shmem_exit(code);
199 :
200 75286 : elog(DEBUG3, "proc_exit(%d): %d callbacks to make",
201 : code, on_proc_exit_index);
202 :
203 : /*
204 : * call all the registered callbacks.
205 : *
206 : * Note that since we decrement on_proc_exit_index each time, if a
207 : * callback calls ereport(ERROR) or ereport(FATAL) then it won't be
208 : * invoked again when control comes back here (nor will the
209 : * previously-completed callbacks). So, an infinite loop should not be
210 : * possible.
211 : */
212 140102 : while (--on_proc_exit_index >= 0)
213 64816 : on_proc_exit_list[on_proc_exit_index].function(code,
214 : on_proc_exit_list[on_proc_exit_index].arg);
215 :
216 75286 : on_proc_exit_index = 0;
217 75286 : }
218 :
219 : /* ------------------
220 : * Run all of the on_shmem_exit routines --- but don't actually exit.
221 : * This is used by the postmaster to re-initialize shared memory and
222 : * semaphores after a backend dies horribly. As with proc_exit(), we
223 : * remove each callback from the list before calling it, to avoid
224 : * infinite loop in case of error.
225 : * ------------------
226 : */
227 : void
228 75296 : shmem_exit(int code)
229 : {
230 75296 : shmem_exit_inprogress = true;
231 :
232 : /*
233 : * Call before_shmem_exit callbacks.
234 : *
235 : * These should be things that need most of the system to still be up and
236 : * working, such as cleanup of temp relations, which requires catalog
237 : * access; or things that need to be completed because later cleanup steps
238 : * depend on them, such as releasing lwlocks.
239 : */
240 75296 : elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
241 : code, before_shmem_exit_index);
242 224768 : while (--before_shmem_exit_index >= 0)
243 149472 : before_shmem_exit_list[before_shmem_exit_index].function(code,
244 : before_shmem_exit_list[before_shmem_exit_index].arg);
245 75296 : before_shmem_exit_index = 0;
246 :
247 : /*
248 : * Call dynamic shared memory callbacks.
249 : *
250 : * These serve the same purpose as late callbacks, but for dynamic shared
251 : * memory segments rather than the main shared memory segment.
252 : * dsm_backend_shutdown() has the same kind of progressive logic we use
253 : * for the main shared memory segment; namely, it unregisters each
254 : * callback before invoking it, so that we don't get stuck in an infinite
255 : * loop if one of those callbacks itself throws an ERROR or FATAL.
256 : *
257 : * Note that explicitly calling this function here is quite different from
258 : * registering it as an on_shmem_exit callback for precisely this reason:
259 : * if one dynamic shared memory callback errors out, the remaining
260 : * callbacks will still be invoked. Thus, hard-coding this call puts it
261 : * equal footing with callbacks for the main shared memory segment.
262 : */
263 75296 : dsm_backend_shutdown();
264 :
265 : /*
266 : * Call on_shmem_exit callbacks.
267 : *
268 : * These are generally releasing low-level shared memory resources. In
269 : * some cases, this is a backstop against the possibility that the early
270 : * callbacks might themselves fail, leading to re-entry to this routine;
271 : * in other cases, it's cleanup that only happens at process exit.
272 : */
273 75296 : elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
274 : code, on_shmem_exit_index);
275 337224 : while (--on_shmem_exit_index >= 0)
276 261928 : on_shmem_exit_list[on_shmem_exit_index].function(code,
277 : on_shmem_exit_list[on_shmem_exit_index].arg);
278 75296 : on_shmem_exit_index = 0;
279 :
280 75296 : shmem_exit_inprogress = false;
281 75296 : }
282 :
283 : /* ----------------------------------------------------------------
284 : * atexit_callback
285 : *
286 : * Backstop to ensure that direct calls of exit() don't mess us up.
287 : *
288 : * Somebody who was being really uncooperative could call _exit(),
289 : * but for that case we have a "dead man switch" that will make the
290 : * postmaster treat it as a crash --- see pmsignal.c.
291 : * ----------------------------------------------------------------
292 : */
293 : static void
294 37614 : atexit_callback(void)
295 : {
296 : /* Clean up everything that must be cleaned up */
297 : /* ... too bad we don't know the real exit code ... */
298 37614 : proc_exit_prepare(-1);
299 37614 : }
300 :
301 : /* ----------------------------------------------------------------
302 : * on_proc_exit
303 : *
304 : * this function adds a callback function to the list of
305 : * functions invoked by proc_exit(). -cim 2/6/90
306 : * ----------------------------------------------------------------
307 : */
308 : void
309 64828 : on_proc_exit(pg_on_exit_callback function, Datum arg)
310 : {
311 64828 : if (on_proc_exit_index >= MAX_ON_EXITS)
312 0 : ereport(FATAL,
313 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
314 : errmsg_internal("out of on_proc_exit slots")));
315 :
316 64828 : on_proc_exit_list[on_proc_exit_index].function = function;
317 64828 : on_proc_exit_list[on_proc_exit_index].arg = arg;
318 :
319 64828 : ++on_proc_exit_index;
320 :
321 64828 : if (!atexit_callback_setup)
322 : {
323 1908 : atexit(atexit_callback);
324 1908 : atexit_callback_setup = true;
325 : }
326 64828 : }
327 :
328 : /* ----------------------------------------------------------------
329 : * before_shmem_exit
330 : *
331 : * Register early callback to perform user-level cleanup,
332 : * e.g. transaction abort, before we begin shutting down
333 : * low-level subsystems.
334 : * ----------------------------------------------------------------
335 : */
336 : void
337 153206 : before_shmem_exit(pg_on_exit_callback function, Datum arg)
338 : {
339 153206 : if (before_shmem_exit_index >= MAX_ON_EXITS)
340 0 : ereport(FATAL,
341 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
342 : errmsg_internal("out of before_shmem_exit slots")));
343 :
344 153206 : before_shmem_exit_list[before_shmem_exit_index].function = function;
345 153206 : before_shmem_exit_list[before_shmem_exit_index].arg = arg;
346 :
347 153206 : ++before_shmem_exit_index;
348 :
349 153206 : if (!atexit_callback_setup)
350 : {
351 0 : atexit(atexit_callback);
352 0 : atexit_callback_setup = true;
353 : }
354 153206 : }
355 :
356 : /* ----------------------------------------------------------------
357 : * on_shmem_exit
358 : *
359 : * Register ordinary callback to perform low-level shutdown
360 : * (e.g. releasing our PGPROC); run after before_shmem_exit
361 : * callbacks and before on_proc_exit callbacks.
362 : * ----------------------------------------------------------------
363 : */
364 : void
365 261958 : on_shmem_exit(pg_on_exit_callback function, Datum arg)
366 : {
367 261958 : if (on_shmem_exit_index >= MAX_ON_EXITS)
368 0 : ereport(FATAL,
369 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
370 : errmsg_internal("out of on_shmem_exit slots")));
371 :
372 261958 : on_shmem_exit_list[on_shmem_exit_index].function = function;
373 261958 : on_shmem_exit_list[on_shmem_exit_index].arg = arg;
374 :
375 261958 : ++on_shmem_exit_index;
376 :
377 261958 : if (!atexit_callback_setup)
378 : {
379 0 : atexit(atexit_callback);
380 0 : atexit_callback_setup = true;
381 : }
382 261958 : }
383 :
384 : /* ----------------------------------------------------------------
385 : * cancel_before_shmem_exit
386 : *
387 : * this function removes a previously-registered before_shmem_exit
388 : * callback. We only look at the latest entry for removal, as we
389 : * expect callers to add and remove temporary before_shmem_exit
390 : * callbacks in strict LIFO order.
391 : * ----------------------------------------------------------------
392 : */
393 : void
394 3734 : cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
395 : {
396 3734 : if (before_shmem_exit_index > 0 &&
397 3734 : before_shmem_exit_list[before_shmem_exit_index - 1].function
398 3734 : == function &&
399 3734 : before_shmem_exit_list[before_shmem_exit_index - 1].arg == arg)
400 3734 : --before_shmem_exit_index;
401 : else
402 0 : elog(ERROR, "before_shmem_exit callback (%p,0x%llx) is not the latest entry",
403 : function, (long long) arg);
404 3734 : }
405 :
406 : /* ----------------------------------------------------------------
407 : * on_exit_reset
408 : *
409 : * this function clears all on_proc_exit() and on_shmem_exit()
410 : * registered functions. This is used just after forking a backend,
411 : * so that the backend doesn't believe it should call the postmaster's
412 : * on-exit routines when it exits...
413 : * ----------------------------------------------------------------
414 : */
415 : void
416 35712 : on_exit_reset(void)
417 : {
418 35712 : before_shmem_exit_index = 0;
419 35712 : on_shmem_exit_index = 0;
420 35712 : on_proc_exit_index = 0;
421 35712 : reset_on_dsm_detach();
422 35712 : }
423 :
424 : /* ----------------------------------------------------------------
425 : * check_on_shmem_exit_lists_are_empty
426 : *
427 : * Debugging check that no shmem cleanup handlers have been registered
428 : * prematurely in the current process.
429 : * ----------------------------------------------------------------
430 : */
431 : void
432 25028 : check_on_shmem_exit_lists_are_empty(void)
433 : {
434 25028 : if (before_shmem_exit_index)
435 0 : elog(FATAL, "before_shmem_exit has been called prematurely");
436 25028 : if (on_shmem_exit_index)
437 0 : elog(FATAL, "on_shmem_exit has been called prematurely");
438 : /* Checking DSM detach state seems unnecessary given the above */
439 25028 : }
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