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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) 1996-2017, 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 {
72 };
73 
77 
78 static int on_proc_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 proc_exit(int code)
100 {
101  /* Clean up everything that must be cleaned up */
102  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 
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  elog(DEBUG3, "exit(%d)", code);
142 
143  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
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  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  InterruptPending = false;
166  ProcDiePending = false;
167  QueryCancelPending = false;
169  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  */
181  /* For the same reason, reset debug_query_string before it's clobbered */
183 
184  /* do our shared memory exits first */
185  shmem_exit(code);
186 
187  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  while (--on_proc_exit_index >= 0)
202 
203  on_proc_exit_index = 0;
204 }
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 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  elog(DEBUG3, "shmem_exit(%d): %d before_shmem_exit callbacks to make",
227  while (--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  */
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  elog(DEBUG3, "shmem_exit(%d): %d on_shmem_exit callbacks to make",
259  code, on_shmem_exit_index);
260  while (--on_shmem_exit_index >= 0)
264 }
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
278 {
279  /* Clean up everything that must be cleaned up */
280  /* ... too bad we don't know the real exit code ... */
281  proc_exit_prepare(-1);
282 }
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
293 {
295  ereport(FATAL,
296  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
297  errmsg_internal("out of on_proc_exit slots")));
298 
301 
303 
305  {
306  atexit(atexit_callback);
307  atexit_callback_setup = true;
308  }
309 }
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
321 {
323  ereport(FATAL,
324  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
325  errmsg_internal("out of before_shmem_exit slots")));
326 
329 
331 
333  {
334  atexit(atexit_callback);
335  atexit_callback_setup = true;
336  }
337 }
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
349 {
351  ereport(FATAL,
352  (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
353  errmsg_internal("out of on_shmem_exit slots")));
354 
357 
359 
361  {
362  atexit(atexit_callback);
363  atexit_callback_setup = true;
364  }
365 }
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
378 {
379  if (before_shmem_exit_index > 0 &&
381  == function &&
384 }
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
397 {
400  on_proc_exit_index = 0;
402 }
void(* pg_on_exit_callback)(int code, Datum arg)
Definition: ipc.h:21
volatile uint32 InterruptHoldoffCount
Definition: globals.c:34
void reset_on_dsm_detach(void)
Definition: dsm.c:1063
static struct ONEXIT on_proc_exit_list[MAX_ON_EXITS]
Definition: ipc.c:74
#define DEBUG3
Definition: elog.h:23
void on_proc_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:292
#define MAX_ON_EXITS
Definition: ipc.c:66
#define mkdir(a, b)
Definition: win32.h:65
static void proc_exit_prepare(int code)
Definition: ipc.c:152
void proc_exit(int code)
Definition: ipc.c:99
int errcode(int sqlerrcode)
Definition: elog.c:575
static int on_shmem_exit_index
Definition: ipc.c:78
int snprintf(char *str, size_t count, const char *fmt,...) pg_attribute_printf(3
void shmem_exit(int code)
Definition: ipc.c:215
volatile bool QueryCancelPending
Definition: globals.c:30
ErrorContextCallback * error_context_stack
Definition: elog.c:88
pg_on_exit_callback function
Definition: ipc.c:70
static bool atexit_callback_setup
Definition: ipc.c:46
void on_exit_reset(void)
Definition: ipc.c:396
#define FATAL
Definition: elog.h:52
void cancel_before_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:377
void on_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:348
void before_shmem_exit(pg_on_exit_callback function, Datum arg)
Definition: ipc.c:320
volatile uint32 CritSectionCount
Definition: globals.c:36
Definition: ipc.c:68
bool IsAutoVacuumWorkerProcess(void)
Definition: autovacuum.c:2988
#define ereport(elevel, rest)
Definition: elog.h:122
void dsm_backend_shutdown(void)
Definition: dsm.c:636
const char * debug_query_string
Definition: postgres.c:83
static struct ONEXIT on_shmem_exit_list[MAX_ON_EXITS]
Definition: ipc.c:75
uintptr_t Datum
Definition: postgres.h:372
#define S_IRWXO
Definition: win32.h:484
static int on_proc_exit_index
Definition: ipc.c:78
volatile bool InterruptPending
Definition: globals.c:29
int errmsg_internal(const char *fmt,...)
Definition: elog.c:827
#define NULL
Definition: c.h:229
bool proc_exit_inprogress
Definition: ipc.c:40
static int before_shmem_exit_index
Definition: ipc.c:78
#define S_IRWXG
Definition: win32.h:480
Datum arg
Definition: ipc.c:71
volatile bool ProcDiePending
Definition: globals.c:31
void * arg
static struct ONEXIT before_shmem_exit_list[MAX_ON_EXITS]
Definition: ipc.c:76
#define elog
Definition: elog.h:219
static void atexit_callback(void)
Definition: ipc.c:277