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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) 1996-2017, 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 : * This flag tracks whether we've called atexit() in the current process
44 : * (or in the parent postmaster).
45 : */
46 : static bool atexit_callback_setup = false;
47 :
48 : /* local functions */
49 : static void proc_exit_prepare(int code);
50 :
51 :
52 : /* ----------------------------------------------------------------
53 : * exit() handling stuff
54 : *
55 : * These functions are in generally the same spirit as atexit(),
56 : * but provide some additional features we need --- in particular,
57 : * we want to register callbacks to invoke when we are disconnecting
58 : * from a broken shared-memory context but not exiting the postmaster.
59 : *
60 : * Callback functions can take zero, one, or two args: the first passed
61 : * arg is the integer exitcode, the second is the Datum supplied when
62 : * the callback was registered.
63 : * ----------------------------------------------------------------
64 : */
65 :
66 : #define MAX_ON_EXITS 20
67 :
68 : struct ONEXIT
69 : {
70 : pg_on_exit_callback function;
71 : Datum arg;
72 : };
73 :
74 : static struct ONEXIT on_proc_exit_list[MAX_ON_EXITS];
75 : static struct ONEXIT on_shmem_exit_list[MAX_ON_EXITS];
76 : static struct ONEXIT before_shmem_exit_list[MAX_ON_EXITS];
77 :
78 : static int on_proc_exit_index,
79 : on_shmem_exit_index,
80 : before_shmem_exit_index;
81 :
82 :
83 : /* ----------------------------------------------------------------
84 : * proc_exit
85 : *
86 : * this function calls all the callbacks registered
87 : * for it (to free resources) and then calls exit.
88 : *
89 : * This should be the only function to call exit().
90 : * -cim 2/6/90
91 : *
92 : * Unfortunately, we can't really guarantee that add-on code
93 : * obeys the rule of not calling exit() directly. So, while
94 : * this is the preferred way out of the system, we also register
95 : * an atexit callback that will make sure cleanup happens.
96 : * ----------------------------------------------------------------
97 : */
98 : void
99 345 : proc_exit(int code)
100 : {
101 : /* Clean up everything that must be cleaned up */
102 345 : proc_exit_prepare(code);
103 :
104 : #ifdef PROFILE_PID_DIR
105 : {
106 : /*
107 : * If we are profiling ourself then gprof's mcleanup() is about to
108 : * write out a profile to ./gmon.out. Since mcleanup() always uses a
109 : * fixed file name, each backend will overwrite earlier profiles. To
110 : * fix that, we create a separate subdirectory for each backend
111 : * (./gprof/pid) and 'cd' to that subdirectory before we exit() - that
112 : * forces mcleanup() to write each profile into its own directory. We
113 : * end up with something like: $PGDATA/gprof/8829/gmon.out
114 : * $PGDATA/gprof/8845/gmon.out ...
115 : *
116 : * To avoid undesirable disk space bloat, autovacuum workers are
117 : * discriminated against: all their gmon.out files go into the same
118 : * subdirectory. Without this, an installation that is "just sitting
119 : * there" nonetheless eats megabytes of disk space every few seconds.
120 : *
121 : * Note that we do this here instead of in an on_proc_exit() callback
122 : * because we want to ensure that this code executes last - we don't
123 : * want to interfere with any other on_proc_exit() callback. For the
124 : * same reason, we do not include it in proc_exit_prepare ... so if
125 : * you are exiting in the "wrong way" you won't drop your profile in a
126 : * nice place.
127 : */
128 : char gprofDirName[32];
129 :
130 : if (IsAutoVacuumWorkerProcess())
131 : snprintf(gprofDirName, 32, "gprof/avworker");
132 : else
133 : snprintf(gprofDirName, 32, "gprof/%d", (int) getpid());
134 :
135 : mkdir("gprof", S_IRWXU | S_IRWXG | S_IRWXO);
136 : mkdir(gprofDirName, S_IRWXU | S_IRWXG | S_IRWXO);
137 : chdir(gprofDirName);
138 : }
139 : #endif
140 :
141 345 : elog(DEBUG3, "exit(%d)", code);
142 :
143 345 : exit(code);
144 : }
145 :
146 : /*
147 : * Code shared between proc_exit and the atexit handler. Note that in
148 : * normal exit through proc_exit, this will actually be called twice ...
149 : * but the second call will have nothing to do.
150 : */
151 : static void
152 691 : proc_exit_prepare(int code)
153 : {
154 : /*
155 : * Once we set this flag, we are committed to exit. Any ereport() will
156 : * NOT send control back to the main loop, but right back here.
157 : */
158 691 : proc_exit_inprogress = true;
159 :
160 : /*
161 : * Forget any pending cancel or die requests; we're doing our best to
162 : * close up shop already. Note that the signal handlers will not set
163 : * these flags again, now that proc_exit_inprogress is set.
164 : */
165 691 : InterruptPending = false;
166 691 : ProcDiePending = false;
167 691 : QueryCancelPending = false;
168 691 : InterruptHoldoffCount = 1;
169 691 : CritSectionCount = 0;
170 :
171 : /*
172 : * Also clear the error context stack, to prevent error callbacks from
173 : * being invoked by any elog/ereport calls made during proc_exit. Whatever
174 : * context they might want to offer is probably not relevant, and in any
175 : * case they are likely to fail outright after we've done things like
176 : * aborting any open transaction. (In normal exit scenarios the context
177 : * stack should be empty anyway, but it might not be in the case of
178 : * elog(FATAL) for example.)
179 : */
180 691 : error_context_stack = NULL;
181 : /* For the same reason, reset debug_query_string before it's clobbered */
182 691 : debug_query_string = NULL;
183 :
184 : /* do our shared memory exits first */
185 691 : shmem_exit(code);
186 :
187 691 : elog(DEBUG3, "proc_exit(%d): %d callbacks to make",
188 : code, on_proc_exit_index);
189 :
190 : /*
191 : * call all the registered callbacks.
192 : *
193 : * Note that since we decrement on_proc_exit_index each time, if a
194 : * callback calls ereport(ERROR) or ereport(FATAL) then it won't be
195 : * invoked again when control comes back here (nor will the
196 : * previously-completed callbacks). So, an infinite loop should not be
197 : * possible.
198 : */
199 2291 : while (--on_proc_exit_index >= 0)
200 909 : (*on_proc_exit_list[on_proc_exit_index].function) (code,
201 : on_proc_exit_list[on_proc_exit_index].arg);
202 :
203 691 : on_proc_exit_index = 0;
204 691 : }
205 :
206 : /* ------------------
207 : * Run all of the on_shmem_exit routines --- but don't actually exit.
208 : * This is used by the postmaster to re-initialize shared memory and
209 : * semaphores after a backend dies horribly. As with proc_exit(), we
210 : * remove each callback from the list before calling it, to avoid
211 : * infinite loop in case of error.
212 : * ------------------
213 : */
214 : void
215 691 : shmem_exit(int code)
216 : {
217 : /*
218 : * Call before_shmem_exit callbacks.
219 : *
220 : * These should be things that need most of the system to still be up and
221 : * working, such as cleanup of temp relations, which requires catalog
222 : * access; or things that need to be completed because later cleanup steps
223 : * depend on them, such as releasing lwlocks.
224 : */
225 691 : elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
226 : code, before_shmem_exit_index);
227 1783 : while (--before_shmem_exit_index >= 0)
228 401 : (*before_shmem_exit_list[before_shmem_exit_index].function) (code,
229 : before_shmem_exit_list[before_shmem_exit_index].arg);
230 691 : before_shmem_exit_index = 0;
231 :
232 : /*
233 : * Call dynamic shared memory callbacks.
234 : *
235 : * These serve the same purpose as late callbacks, but for dynamic shared
236 : * memory segments rather than the main shared memory segment.
237 : * dsm_backend_shutdown() has the same kind of progressive logic we use
238 : * for the main shared memory segment; namely, it unregisters each
239 : * callback before invoking it, so that we don't get stuck in an infinite
240 : * loop if one of those callbacks itself throws an ERROR or FATAL.
241 : *
242 : * Note that explicitly calling this function here is quite different from
243 : * registering it as an on_shmem_exit callback for precisely this reason:
244 : * if one dynamic shared memory callback errors out, the remaining
245 : * callbacks will still be invoked. Thus, hard-coding this call puts it
246 : * equal footing with callbacks for the main shared memory segment.
247 : */
248 691 : dsm_backend_shutdown();
249 :
250 : /*
251 : * Call on_shmem_exit callbacks.
252 : *
253 : * These are generally releasing low-level shared memory resources. In
254 : * some cases, this is a backstop against the possibility that the early
255 : * callbacks might themselves fail, leading to re-entry to this routine;
256 : * in other cases, it's cleanup that only happens at process exit.
257 : */
258 691 : elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
259 : code, on_shmem_exit_index);
260 3454 : while (--on_shmem_exit_index >= 0)
261 2072 : (*on_shmem_exit_list[on_shmem_exit_index].function) (code,
262 : on_shmem_exit_list[on_shmem_exit_index].arg);
263 691 : on_shmem_exit_index = 0;
264 691 : }
265 :
266 : /* ----------------------------------------------------------------
267 : * atexit_callback
268 : *
269 : * Backstop to ensure that direct calls of exit() don't mess us up.
270 : *
271 : * Somebody who was being really uncooperative could call _exit(),
272 : * but for that case we have a "dead man switch" that will make the
273 : * postmaster treat it as a crash --- see pmsignal.c.
274 : * ----------------------------------------------------------------
275 : */
276 : static void
277 346 : atexit_callback(void)
278 : {
279 : /* Clean up everything that must be cleaned up */
280 : /* ... too bad we don't know the real exit code ... */
281 346 : proc_exit_prepare(-1);
282 346 : }
283 :
284 : /* ----------------------------------------------------------------
285 : * on_proc_exit
286 : *
287 : * this function adds a callback function to the list of
288 : * functions invoked by proc_exit(). -cim 2/6/90
289 : * ----------------------------------------------------------------
290 : */
291 : void
292 909 : on_proc_exit(pg_on_exit_callback function, Datum arg)
293 : {
294 909 : if (on_proc_exit_index >= MAX_ON_EXITS)
295 0 : ereport(FATAL,
296 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
297 : errmsg_internal("out of on_proc_exit slots")));
298 :
299 909 : on_proc_exit_list[on_proc_exit_index].function = function;
300 909 : on_proc_exit_list[on_proc_exit_index].arg = arg;
301 :
302 909 : ++on_proc_exit_index;
303 :
304 909 : if (!atexit_callback_setup)
305 : {
306 5 : atexit(atexit_callback);
307 5 : atexit_callback_setup = true;
308 : }
309 909 : }
310 :
311 : /* ----------------------------------------------------------------
312 : * before_shmem_exit
313 : *
314 : * Register early callback to perform user-level cleanup,
315 : * e.g. transaction abort, before we begin shutting down
316 : * low-level subsystems.
317 : * ----------------------------------------------------------------
318 : */
319 : void
320 513 : before_shmem_exit(pg_on_exit_callback function, Datum arg)
321 : {
322 513 : if (before_shmem_exit_index >= MAX_ON_EXITS)
323 0 : ereport(FATAL,
324 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
325 : errmsg_internal("out of before_shmem_exit slots")));
326 :
327 513 : before_shmem_exit_list[before_shmem_exit_index].function = function;
328 513 : before_shmem_exit_list[before_shmem_exit_index].arg = arg;
329 :
330 513 : ++before_shmem_exit_index;
331 :
332 513 : if (!atexit_callback_setup)
333 : {
334 0 : atexit(atexit_callback);
335 0 : atexit_callback_setup = true;
336 : }
337 513 : }
338 :
339 : /* ----------------------------------------------------------------
340 : * on_shmem_exit
341 : *
342 : * Register ordinary callback to perform low-level shutdown
343 : * (e.g. releasing our PGPROC); run after before_shmem_exit
344 : * callbacks and before on_proc_exit callbacks.
345 : * ----------------------------------------------------------------
346 : */
347 : void
348 2072 : on_shmem_exit(pg_on_exit_callback function, Datum arg)
349 : {
350 2072 : if (on_shmem_exit_index >= MAX_ON_EXITS)
351 0 : ereport(FATAL,
352 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
353 : errmsg_internal("out of on_shmem_exit slots")));
354 :
355 2072 : on_shmem_exit_list[on_shmem_exit_index].function = function;
356 2072 : on_shmem_exit_list[on_shmem_exit_index].arg = arg;
357 :
358 2072 : ++on_shmem_exit_index;
359 :
360 2072 : if (!atexit_callback_setup)
361 : {
362 0 : atexit(atexit_callback);
363 0 : atexit_callback_setup = true;
364 : }
365 2072 : }
366 :
367 : /* ----------------------------------------------------------------
368 : * cancel_before_shmem_exit
369 : *
370 : * this function removes a previously-registed before_shmem_exit
371 : * callback. For simplicity, only the latest entry can be
372 : * removed. (We could work harder but there is no need for
373 : * current uses.)
374 : * ----------------------------------------------------------------
375 : */
376 : void
377 112 : cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
378 : {
379 224 : if (before_shmem_exit_index > 0 &&
380 112 : before_shmem_exit_list[before_shmem_exit_index - 1].function
381 112 : == function &&
382 112 : before_shmem_exit_list[before_shmem_exit_index - 1].arg == arg)
383 112 : --before_shmem_exit_index;
384 112 : }
385 :
386 : /* ----------------------------------------------------------------
387 : * on_exit_reset
388 : *
389 : * this function clears all on_proc_exit() and on_shmem_exit()
390 : * registered functions. This is used just after forking a backend,
391 : * so that the backend doesn't believe it should call the postmaster's
392 : * on-exit routines when it exits...
393 : * ----------------------------------------------------------------
394 : */
395 : void
396 341 : on_exit_reset(void)
397 : {
398 341 : before_shmem_exit_index = 0;
399 341 : on_shmem_exit_index = 0;
400 341 : on_proc_exit_index = 0;
401 341 : reset_on_dsm_detach();
402 341 : }
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