TLA 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) 1996-2023, 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 CBC 14589 : proc_exit(int code)
105 : {
106 : /* Clean up everything that must be cleaned up */
107 14589 : proc_exit_prepare(code);
108 :
109 : #ifdef PROFILE_PID_DIR
110 : {
111 : /*
112 : * If we are profiling ourself then gprof's mcleanup() is about to
113 : * write out a profile to ./gmon.out. Since mcleanup() always uses a
114 : * fixed file name, each backend will overwrite earlier profiles. To
115 : * fix that, we create a separate subdirectory for each backend
116 : * (./gprof/pid) and 'cd' to that subdirectory before we exit() - that
117 : * forces mcleanup() to write each profile into its own directory. We
118 : * end up with something like: $PGDATA/gprof/8829/gmon.out
119 : * $PGDATA/gprof/8845/gmon.out ...
120 : *
121 : * To avoid undesirable disk space bloat, autovacuum workers are
122 : * discriminated against: all their gmon.out files go into the same
123 : * subdirectory. Without this, an installation that is "just sitting
124 : * there" nonetheless eats megabytes of disk space every few seconds.
125 : *
126 : * Note that we do this here instead of in an on_proc_exit() callback
127 : * because we want to ensure that this code executes last - we don't
128 : * want to interfere with any other on_proc_exit() callback. For the
129 : * same reason, we do not include it in proc_exit_prepare ... so if
130 : * you are exiting in the "wrong way" you won't drop your profile in a
131 : * nice place.
132 : */
133 : char gprofDirName[32];
134 :
135 : if (IsAutoVacuumWorkerProcess())
136 : snprintf(gprofDirName, 32, "gprof/avworker");
137 : else
138 : snprintf(gprofDirName, 32, "gprof/%d", (int) getpid());
139 :
140 : /*
141 : * Use mkdir() instead of MakePGDirectory() since we aren't making a
142 : * PG directory here.
143 : */
144 : mkdir("gprof", S_IRWXU | S_IRWXG | S_IRWXO);
145 : mkdir(gprofDirName, S_IRWXU | S_IRWXG | S_IRWXO);
146 : chdir(gprofDirName);
147 : }
148 : #endif
149 :
150 14589 : elog(DEBUG3, "exit(%d)", code);
151 :
152 14589 : exit(code);
153 : }
154 :
155 : /*
156 : * Code shared between proc_exit and the atexit handler. Note that in
157 : * normal exit through proc_exit, this will actually be called twice ...
158 : * but the second call will have nothing to do.
159 : */
160 : static void
161 29149 : proc_exit_prepare(int code)
162 : {
163 : /*
164 : * Once we set this flag, we are committed to exit. Any ereport() will
165 : * NOT send control back to the main loop, but right back here.
166 : */
167 29149 : proc_exit_inprogress = true;
168 :
169 : /*
170 : * Forget any pending cancel or die requests; we're doing our best to
171 : * close up shop already. Note that the signal handlers will not set
172 : * these flags again, now that proc_exit_inprogress is set.
173 : */
174 29149 : InterruptPending = false;
175 29149 : ProcDiePending = false;
176 29149 : QueryCancelPending = false;
177 29149 : InterruptHoldoffCount = 1;
178 29149 : CritSectionCount = 0;
179 :
180 : /*
181 : * Also clear the error context stack, to prevent error callbacks from
182 : * being invoked by any elog/ereport calls made during proc_exit. Whatever
183 : * context they might want to offer is probably not relevant, and in any
184 : * case they are likely to fail outright after we've done things like
185 : * aborting any open transaction. (In normal exit scenarios the context
186 : * stack should be empty anyway, but it might not be in the case of
187 : * elog(FATAL) for example.)
188 : */
189 29149 : error_context_stack = NULL;
190 : /* For the same reason, reset debug_query_string before it's clobbered */
191 29149 : debug_query_string = NULL;
192 :
193 : /* do our shared memory exits first */
194 29149 : shmem_exit(code);
195 :
196 29149 : elog(DEBUG3, "proc_exit(%d): %d callbacks to make",
197 : code, on_proc_exit_index);
198 :
199 : /*
200 : * call all the registered callbacks.
201 : *
202 : * Note that since we decrement on_proc_exit_index each time, if a
203 : * callback calls ereport(ERROR) or ereport(FATAL) then it won't be
204 : * invoked again when control comes back here (nor will the
205 : * previously-completed callbacks). So, an infinite loop should not be
206 : * possible.
207 : */
208 53952 : while (--on_proc_exit_index >= 0)
209 24803 : on_proc_exit_list[on_proc_exit_index].function(code,
210 : on_proc_exit_list[on_proc_exit_index].arg);
211 :
212 29149 : on_proc_exit_index = 0;
213 29149 : }
214 :
215 : /* ------------------
216 : * Run all of the on_shmem_exit routines --- but don't actually exit.
217 : * This is used by the postmaster to re-initialize shared memory and
218 : * semaphores after a backend dies horribly. As with proc_exit(), we
219 : * remove each callback from the list before calling it, to avoid
220 : * infinite loop in case of error.
221 : * ------------------
222 : */
223 : void
224 29153 : shmem_exit(int code)
225 : {
226 29153 : shmem_exit_inprogress = true;
227 :
228 : /*
229 : * Call before_shmem_exit callbacks.
230 : *
231 : * These should be things that need most of the system to still be up and
232 : * working, such as cleanup of temp relations, which requires catalog
233 : * access; or things that need to be completed because later cleanup steps
234 : * depend on them, such as releasing lwlocks.
235 : */
236 29153 : elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
237 : code, before_shmem_exit_index);
238 86281 : while (--before_shmem_exit_index >= 0)
239 57128 : before_shmem_exit_list[before_shmem_exit_index].function(code,
240 : before_shmem_exit_list[before_shmem_exit_index].arg);
241 29153 : before_shmem_exit_index = 0;
242 :
243 : /*
244 : * Call dynamic shared memory callbacks.
245 : *
246 : * These serve the same purpose as late callbacks, but for dynamic shared
247 : * memory segments rather than the main shared memory segment.
248 : * dsm_backend_shutdown() has the same kind of progressive logic we use
249 : * for the main shared memory segment; namely, it unregisters each
250 : * callback before invoking it, so that we don't get stuck in an infinite
251 : * loop if one of those callbacks itself throws an ERROR or FATAL.
252 : *
253 : * Note that explicitly calling this function here is quite different from
254 : * registering it as an on_shmem_exit callback for precisely this reason:
255 : * if one dynamic shared memory callback errors out, the remaining
256 : * callbacks will still be invoked. Thus, hard-coding this call puts it
257 : * equal footing with callbacks for the main shared memory segment.
258 : */
259 29153 : dsm_backend_shutdown();
260 :
261 : /*
262 : * Call on_shmem_exit callbacks.
263 : *
264 : * These are generally releasing low-level shared memory resources. In
265 : * some cases, this is a backstop against the possibility that the early
266 : * callbacks might themselves fail, leading to re-entry to this routine;
267 : * in other cases, it's cleanup that only happens at process exit.
268 : */
269 29153 : elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
270 : code, on_shmem_exit_index);
271 118809 : while (--on_shmem_exit_index >= 0)
272 89656 : on_shmem_exit_list[on_shmem_exit_index].function(code,
273 : on_shmem_exit_list[on_shmem_exit_index].arg);
274 29153 : on_shmem_exit_index = 0;
275 :
276 29153 : shmem_exit_inprogress = false;
277 29153 : }
278 :
279 : /* ----------------------------------------------------------------
280 : * atexit_callback
281 : *
282 : * Backstop to ensure that direct calls of exit() don't mess us up.
283 : *
284 : * Somebody who was being really uncooperative could call _exit(),
285 : * but for that case we have a "dead man switch" that will make the
286 : * postmaster treat it as a crash --- see pmsignal.c.
287 : * ----------------------------------------------------------------
288 : */
289 : static void
290 14560 : atexit_callback(void)
291 : {
292 : /* Clean up everything that must be cleaned up */
293 : /* ... too bad we don't know the real exit code ... */
294 14560 : proc_exit_prepare(-1);
295 14560 : }
296 :
297 : /* ----------------------------------------------------------------
298 : * on_proc_exit
299 : *
300 : * this function adds a callback function to the list of
301 : * functions invoked by proc_exit(). -cim 2/6/90
302 : * ----------------------------------------------------------------
303 : */
304 : void
305 24803 : on_proc_exit(pg_on_exit_callback function, Datum arg)
306 : {
307 24803 : if (on_proc_exit_index >= MAX_ON_EXITS)
308 UBC 0 : ereport(FATAL,
309 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
310 : errmsg_internal("out of on_proc_exit slots")));
311 :
312 CBC 24803 : on_proc_exit_list[on_proc_exit_index].function = function;
313 24803 : on_proc_exit_list[on_proc_exit_index].arg = arg;
314 :
315 24803 : ++on_proc_exit_index;
316 :
317 24803 : if (!atexit_callback_setup)
318 : {
319 1828 : atexit(atexit_callback);
320 1828 : atexit_callback_setup = true;
321 : }
322 24803 : }
323 :
324 : /* ----------------------------------------------------------------
325 : * before_shmem_exit
326 : *
327 : * Register early callback to perform user-level cleanup,
328 : * e.g. transaction abort, before we begin shutting down
329 : * low-level subsystems.
330 : * ----------------------------------------------------------------
331 : */
332 : void
333 62199 : before_shmem_exit(pg_on_exit_callback function, Datum arg)
334 : {
335 62199 : if (before_shmem_exit_index >= MAX_ON_EXITS)
336 UBC 0 : ereport(FATAL,
337 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
338 : errmsg_internal("out of before_shmem_exit slots")));
339 :
340 CBC 62199 : before_shmem_exit_list[before_shmem_exit_index].function = function;
341 62199 : before_shmem_exit_list[before_shmem_exit_index].arg = arg;
342 :
343 62199 : ++before_shmem_exit_index;
344 :
345 62199 : if (!atexit_callback_setup)
346 : {
347 UBC 0 : atexit(atexit_callback);
348 0 : atexit_callback_setup = true;
349 : }
350 CBC 62199 : }
351 :
352 : /* ----------------------------------------------------------------
353 : * on_shmem_exit
354 : *
355 : * Register ordinary callback to perform low-level shutdown
356 : * (e.g. releasing our PGPROC); run after before_shmem_exit
357 : * callbacks and before on_proc_exit callbacks.
358 : * ----------------------------------------------------------------
359 : */
360 : void
361 89656 : on_shmem_exit(pg_on_exit_callback function, Datum arg)
362 : {
363 89656 : if (on_shmem_exit_index >= MAX_ON_EXITS)
364 UBC 0 : ereport(FATAL,
365 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
366 : errmsg_internal("out of on_shmem_exit slots")));
367 :
368 CBC 89656 : on_shmem_exit_list[on_shmem_exit_index].function = function;
369 89656 : on_shmem_exit_list[on_shmem_exit_index].arg = arg;
370 :
371 89656 : ++on_shmem_exit_index;
372 :
373 89656 : if (!atexit_callback_setup)
374 : {
375 UBC 0 : atexit(atexit_callback);
376 0 : atexit_callback_setup = true;
377 : }
378 CBC 89656 : }
379 :
380 : /* ----------------------------------------------------------------
381 : * cancel_before_shmem_exit
382 : *
383 : * this function removes a previously-registered before_shmem_exit
384 : * callback. We only look at the latest entry for removal, as we
385 : * expect callers to add and remove temporary before_shmem_exit
386 : * callbacks in strict LIFO order.
387 : * ----------------------------------------------------------------
388 : */
389 : void
390 5071 : cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
391 : {
392 5071 : if (before_shmem_exit_index > 0 &&
393 5071 : before_shmem_exit_list[before_shmem_exit_index - 1].function
394 5071 : == function &&
395 5071 : before_shmem_exit_list[before_shmem_exit_index - 1].arg == arg)
396 5071 : --before_shmem_exit_index;
397 : else
398 UBC 0 : elog(ERROR, "before_shmem_exit callback (%p,0x%llx) is not the latest entry",
399 : function, (long long) arg);
400 CBC 5071 : }
401 :
402 : /* ----------------------------------------------------------------
403 : * on_exit_reset
404 : *
405 : * this function clears all on_proc_exit() and on_shmem_exit()
406 : * registered functions. This is used just after forking a backend,
407 : * so that the backend doesn't believe it should call the postmaster's
408 : * on-exit routines when it exits...
409 : * ----------------------------------------------------------------
410 : */
411 : void
412 12732 : on_exit_reset(void)
413 : {
414 12732 : before_shmem_exit_index = 0;
415 12732 : on_shmem_exit_index = 0;
416 12732 : on_proc_exit_index = 0;
417 12732 : reset_on_dsm_detach();
418 12732 : }
419 :
420 : /* ----------------------------------------------------------------
421 : * check_on_shmem_exit_lists_are_empty
422 : *
423 : * Debugging check that no shmem cleanup handlers have been registered
424 : * prematurely in the current process.
425 : * ----------------------------------------------------------------
426 : */
427 : void
428 8654 : check_on_shmem_exit_lists_are_empty(void)
429 : {
430 8654 : if (before_shmem_exit_index)
431 UBC 0 : elog(FATAL, "before_shmem_exit has been called prematurely");
432 CBC 8654 : if (on_shmem_exit_index)
433 UBC 0 : elog(FATAL, "on_shmem_exit has been called prematurely");
434 : /* Checking DSM detach state seems unnecessary given the above */
435 CBC 8654 : }
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