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ipc.c
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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) 1996-2024, 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 {
77 };
78 
82 
83 static int on_proc_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 proc_exit(int code)
105 {
106  /* not safe if forked by system(), etc. */
107  if (MyProcPid != (int) getpid())
108  elog(PANIC, "proc_exit() called in child process");
109 
110  /* Clean up everything that must be cleaned up */
111  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 
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  elog(DEBUG3, "exit(%d)", code);
155 
156  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
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  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  InterruptPending = false;
179  ProcDiePending = false;
180  QueryCancelPending = false;
182  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  error_context_stack = NULL;
194  /* For the same reason, reset debug_query_string before it's clobbered */
195  debug_query_string = NULL;
196 
197  /* do our shared memory exits first */
198  shmem_exit(code);
199 
200  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  while (--on_proc_exit_index >= 0)
215 
216  on_proc_exit_index = 0;
217 }
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 shmem_exit(int code)
229 {
230  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  elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
242  while (--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  */
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  elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
274  code, on_shmem_exit_index);
275  while (--on_shmem_exit_index >= 0)
279 
280  shmem_exit_inprogress = false;
281 }
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
295 {
296  /* Clean up everything that must be cleaned up */
297  /* ... too bad we don't know the real exit code ... */
298  proc_exit_prepare(-1);
299 }
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
310 {
312  ereport(FATAL,
313  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
314  errmsg_internal("out of on_proc_exit slots")));
315 
318 
320 
322  {
323  atexit(atexit_callback);
324  atexit_callback_setup = true;
325  }
326 }
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
338 {
340  ereport(FATAL,
341  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
342  errmsg_internal("out of before_shmem_exit slots")));
343 
346 
348 
350  {
351  atexit(atexit_callback);
352  atexit_callback_setup = true;
353  }
354 }
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
366 {
368  ereport(FATAL,
369  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
370  errmsg_internal("out of on_shmem_exit slots")));
371 
374 
376 
378  {
379  atexit(atexit_callback);
380  atexit_callback_setup = true;
381  }
382 }
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
395 {
396  if (before_shmem_exit_index > 0 &&
398  == function &&
401  else
402  elog(ERROR, "before_shmem_exit callback (%p,0x%llx) is not the latest entry",
403  function, (long long) arg);
404 }
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
417 {
420  on_proc_exit_index = 0;
422 }
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
433 {
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 */
439 }
void dsm_backend_shutdown(void)
Definition: dsm.c:757
void reset_on_dsm_detach(void)
Definition: dsm.c:1170
int errmsg_internal(const char *fmt,...)
Definition: elog.c:1157
ErrorContextCallback * error_context_stack
Definition: elog.c:94
int errcode(int sqlerrcode)
Definition: elog.c:857
#define DEBUG3
Definition: elog.h:28
#define FATAL
Definition: elog.h:41
#define PANIC
Definition: elog.h:42
#define ERROR
Definition: elog.h:39
#define elog(elevel,...)
Definition: elog.h:224
#define ereport(elevel,...)
Definition: elog.h:149
volatile sig_atomic_t InterruptPending
Definition: globals.c:30
volatile uint32 InterruptHoldoffCount
Definition: globals.c:41
int MyProcPid
Definition: globals.c:45
volatile uint32 CritSectionCount
Definition: globals.c:43
volatile sig_atomic_t QueryCancelPending
Definition: globals.c:31
volatile sig_atomic_t ProcDiePending
Definition: globals.c:32
void check_on_shmem_exit_lists_are_empty(void)
Definition: ipc.c:432
void on_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:365
static bool atexit_callback_setup
Definition: ipc.c:51
bool shmem_exit_inprogress
Definition: ipc.c:45
void on_proc_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:309
static struct ONEXIT on_proc_exit_list[MAX_ON_EXITS]
Definition: ipc.c:79
void cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:394
static void atexit_callback(void)
Definition: ipc.c:294
bool proc_exit_inprogress
Definition: ipc.c:40
#define MAX_ON_EXITS
Definition: ipc.c:71
static int before_shmem_exit_index
Definition: ipc.c:85
void shmem_exit(int code)
Definition: ipc.c:228
void before_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:337
static int on_shmem_exit_index
Definition: ipc.c:84
void on_exit_reset(void)
Definition: ipc.c:416
static struct ONEXIT before_shmem_exit_list[MAX_ON_EXITS]
Definition: ipc.c:81
void proc_exit(int code)
Definition: ipc.c:104
static int on_proc_exit_index
Definition: ipc.c:83
static struct ONEXIT on_shmem_exit_list[MAX_ON_EXITS]
Definition: ipc.c:80
static void proc_exit_prepare(int code)
Definition: ipc.c:165
void(* pg_on_exit_callback)(int code, Datum arg)
Definition: ipc.h:21
exit(1)
#define AmAutoVacuumWorkerProcess()
Definition: miscadmin.h:375
void * arg
#define snprintf
Definition: port.h:238
const char * debug_query_string
Definition: postgres.c:87
uintptr_t Datum
Definition: postgres.h:64
Definition: ipc.c:74
Datum arg
Definition: ipc.c:76
pg_on_exit_callback function
Definition: ipc.c:75
#define S_IRWXG
Definition: win32_port.h:310
#define S_IRWXO
Definition: win32_port.h:322
#define mkdir(a, b)
Definition: win32_port.h:80
#define S_IRWXU
Definition: win32_port.h:298