1/*-------------------------------------------------------------------------
4 * POSTGRES inter-process communication definitions.
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.
11 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
12 * Portions Copyright (c) 1994, Regents of the University of California
16 * src/backend/storage/ipc/ipc.c
18 *-------------------------------------------------------------------------
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...
43 * Set when shmem_exit() is in progress.
48 * This flag tracks whether we've called atexit() in the current process
49 * (or in the parent postmaster).
57/* ----------------------------------------------------------------
58 * exit() handling stuff
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.
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 * ----------------------------------------------------------------
71 #define MAX_ON_EXITS 20
88/* ----------------------------------------------------------------
91 * this function calls all the callbacks registered
92 * for it (to free resources) and then calls exit.
94 * This should be the only function to call exit().
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 * ----------------------------------------------------------------
106 /* not safe if forked by system(), etc. */
108 elog(
PANIC,
"proc_exit() called in child process");
110 /* Clean up everything that must be cleaned up */
113#ifdef PROFILE_PID_DIR
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 ...
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.
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
137 char gprofDirName[32];
140 snprintf(gprofDirName, 32,
"gprof/avworker");
142 snprintf(gprofDirName, 32,
"gprof/%d", (
int) getpid());
145 * Use mkdir() instead of MakePGDirectory() since we aren't making a
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.
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.
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.
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.)
194 /* For the same reason, reset debug_query_string before it's clobbered */
197 /* do our shared memory exits first */
200 elog(
DEBUG3,
"proc_exit(%d): %d callbacks to make",
204 * call all the registered callbacks.
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
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.
233 * Call before_shmem_exit callbacks.
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.
240 elog(
DEBUG3,
"shmem_exit(%d): %d before_shmem_exit callbacks to make",
248 * Call dynamic shared memory callbacks.
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.
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.
266 * Call on_shmem_exit callbacks.
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.
273 elog(
DEBUG3,
"shmem_exit(%d): %d on_shmem_exit callbacks to make",
283/* ----------------------------------------------------------------
286 * Backstop to ensure that direct calls of exit() don't mess us up.
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 * ----------------------------------------------------------------
296 /* Clean up everything that must be cleaned up */
297 /* ... too bad we don't know the real exit code ... */
301/* ----------------------------------------------------------------
304 * this function adds a callback function to the list of
305 * functions invoked by proc_exit(). -cim 2/6/90
306 * ----------------------------------------------------------------
313 (
errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
328/* ----------------------------------------------------------------
331 * Register early callback to perform user-level cleanup,
332 * e.g. transaction abort, before we begin shutting down
333 * low-level subsystems.
334 * ----------------------------------------------------------------
341 (
errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
356/* ----------------------------------------------------------------
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 * ----------------------------------------------------------------
369 (
errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
384/* ----------------------------------------------------------------
385 * cancel_before_shmem_exit
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 * ----------------------------------------------------------------
402 elog(
ERROR,
"before_shmem_exit callback (%p,0x%" PRIx64
") is not the latest entry",
406/* ----------------------------------------------------------------
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 * ----------------------------------------------------------------
424/* ----------------------------------------------------------------
425 * check_on_shmem_exit_lists_are_empty
427 * Debugging check that no shmem cleanup handlers have been registered
428 * prematurely in the current process.
429 * ----------------------------------------------------------------
435 elog(
FATAL,
"before_shmem_exit has been called prematurely");
437 elog(
FATAL,
"on_shmem_exit has been called prematurely");
438 /* Checking DSM detach state seems unnecessary given the above */
void dsm_backend_shutdown(void)
void reset_on_dsm_detach(void)
int errmsg_internal(const char *fmt,...)
ErrorContextCallback * error_context_stack
int errcode(int sqlerrcode)
#define ereport(elevel,...)
volatile sig_atomic_t InterruptPending
volatile uint32 InterruptHoldoffCount
volatile uint32 CritSectionCount
volatile sig_atomic_t QueryCancelPending
volatile sig_atomic_t ProcDiePending
void check_on_shmem_exit_lists_are_empty(void)
void on_shmem_exit(pg_on_exit_callback function, Datum arg)
static bool atexit_callback_setup
bool shmem_exit_inprogress
void on_proc_exit(pg_on_exit_callback function, Datum arg)
static struct ONEXIT on_proc_exit_list[MAX_ON_EXITS]
void cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
static void atexit_callback(void)
bool proc_exit_inprogress
static int before_shmem_exit_index
void shmem_exit(int code)
void before_shmem_exit(pg_on_exit_callback function, Datum arg)
static int on_shmem_exit_index
static struct ONEXIT before_shmem_exit_list[MAX_ON_EXITS]
static int on_proc_exit_index
static struct ONEXIT on_shmem_exit_list[MAX_ON_EXITS]
static void proc_exit_prepare(int code)
void(* pg_on_exit_callback)(int code, Datum arg)
#define AmAutoVacuumWorkerProcess()
on_exit_nicely_callback function
const char * debug_query_string
pg_on_exit_callback function