PostgreSQL Source Code  git master
timeout.c File Reference
#include "postgres.h"
#include <sys/time.h>
#include "miscadmin.h"
#include "storage/proc.h"
#include "utils/timeout.h"
#include "utils/timestamp.h"
Include dependency graph for timeout.c:

Go to the source code of this file.

Data Structures

struct  timeout_params
 

Macros

#define disable_alarm()   (alarm_enabled = false)
 
#define enable_alarm()   (alarm_enabled = true)
 

Typedefs

typedef struct timeout_params timeout_params
 

Functions

static int find_active_timeout (TimeoutId id)
 
static void insert_timeout (TimeoutId id, int index)
 
static void remove_timeout_index (int index)
 
static void enable_timeout (TimeoutId id, TimestampTz now, TimestampTz fin_time, int interval_in_ms)
 
static void schedule_alarm (TimestampTz now)
 
static void handle_sig_alarm (SIGNAL_ARGS)
 
void InitializeTimeouts (void)
 
TimeoutId RegisterTimeout (TimeoutId id, timeout_handler_proc handler)
 
void reschedule_timeouts (void)
 
void enable_timeout_after (TimeoutId id, int delay_ms)
 
void enable_timeout_every (TimeoutId id, TimestampTz fin_time, int delay_ms)
 
void enable_timeout_at (TimeoutId id, TimestampTz fin_time)
 
void enable_timeouts (const EnableTimeoutParams *timeouts, int count)
 
void disable_timeout (TimeoutId id, bool keep_indicator)
 
void disable_timeouts (const DisableTimeoutParams *timeouts, int count)
 
void disable_all_timeouts (bool keep_indicators)
 
bool get_timeout_active (TimeoutId id)
 
bool get_timeout_indicator (TimeoutId id, bool reset_indicator)
 
TimestampTz get_timeout_start_time (TimeoutId id)
 
TimestampTz get_timeout_finish_time (TimeoutId id)
 

Variables

static timeout_params all_timeouts [MAX_TIMEOUTS]
 
static bool all_timeouts_initialized = false
 
static volatile int num_active_timeouts = 0
 
static timeout_params *volatile active_timeouts [MAX_TIMEOUTS]
 
static volatile sig_atomic_t alarm_enabled = false
 
static volatile sig_atomic_t signal_pending = false
 
static volatile TimestampTz signal_due_at = 0
 

Macro Definition Documentation

◆ disable_alarm

#define disable_alarm ( )    (alarm_enabled = false)

Definition at line 69 of file timeout.c.

◆ enable_alarm

#define enable_alarm ( )    (alarm_enabled = true)

Definition at line 70 of file timeout.c.

Typedef Documentation

◆ timeout_params

Function Documentation

◆ disable_all_timeouts()

void disable_all_timeouts ( bool  keep_indicators)

Definition at line 755 of file timeout.c.

756 {
757  int i;
758 
759  disable_alarm();
760 
761  /*
762  * We used to disable the timer interrupt here, but in common usage
763  * patterns it's cheaper to leave it enabled; that may save us from having
764  * to enable it again shortly. See comments in schedule_alarm().
765  */
766 
768 
769  for (i = 0; i < MAX_TIMEOUTS; i++)
770  {
771  all_timeouts[i].active = false;
772  if (!keep_indicators)
773  all_timeouts[i].indicator = false;
774  }
775 }
int i
Definition: isn.c:73
volatile bool active
Definition: timeout.c:31
volatile bool indicator
Definition: timeout.c:32
#define disable_alarm()
Definition: timeout.c:69
static timeout_params all_timeouts[MAX_TIMEOUTS]
Definition: timeout.c:45
static volatile int num_active_timeouts
Definition: timeout.c:52
@ MAX_TIMEOUTS
Definition: timeout.h:41

References timeout_params::active, all_timeouts, disable_alarm, i, timeout_params::indicator, MAX_TIMEOUTS, and num_active_timeouts.

Referenced by AutoVacLauncherMain(), PostgresMain(), ResolveRecoveryConflictWithBufferPin(), and ResolveRecoveryConflictWithLock().

◆ disable_timeout()

void disable_timeout ( TimeoutId  id,
bool  keep_indicator 
)

Definition at line 689 of file timeout.c.

690 {
691  /* Assert request is sane */
693  Assert(all_timeouts[id].timeout_handler != NULL);
694 
695  /* Disable timeout interrupts for safety. */
696  disable_alarm();
697 
698  /* Find the timeout and remove it from the active list. */
699  if (all_timeouts[id].active)
701 
702  /* Mark it inactive, whether it was active or not. */
703  if (!keep_indicator)
704  all_timeouts[id].indicator = false;
705 
706  /* Reschedule the interrupt, if any timeouts remain active. */
707  if (num_active_timeouts > 0)
709 }
TimestampTz GetCurrentTimestamp(void)
Definition: timestamp.c:1574
Assert(fmt[strlen(fmt) - 1] !='\n')
static int find_active_timeout(TimeoutId id)
Definition: timeout.c:96
static bool all_timeouts_initialized
Definition: timeout.c:46
static void schedule_alarm(TimestampTz now)
Definition: timeout.c:210
static void remove_timeout_index(int index)
Definition: timeout.c:137

References all_timeouts, all_timeouts_initialized, Assert(), disable_alarm, find_active_timeout(), GetCurrentTimestamp(), timeout_params::indicator, num_active_timeouts, remove_timeout_index(), and schedule_alarm().

Referenced by BackendInitialize(), begin_startup_progress_phase(), disable_statement_timeout(), enable_statement_timeout(), PerformAuthentication(), PostgresMain(), and ProcSleep().

◆ disable_timeouts()

void disable_timeouts ( const DisableTimeoutParams timeouts,
int  count 
)

Definition at line 722 of file timeout.c.

723 {
724  int i;
725 
727 
728  /* Disable timeout interrupts for safety. */
729  disable_alarm();
730 
731  /* Cancel the timeout(s). */
732  for (i = 0; i < count; i++)
733  {
734  TimeoutId id = timeouts[i].id;
735 
736  Assert(all_timeouts[id].timeout_handler != NULL);
737 
738  if (all_timeouts[id].active)
740 
741  if (!timeouts[i].keep_indicator)
742  all_timeouts[id].indicator = false;
743  }
744 
745  /* Reschedule the interrupt, if any timeouts remain active. */
746  if (num_active_timeouts > 0)
748 }
TimeoutId id
Definition: timeout.h:70
TimeoutId
Definition: timeout.h:24

References all_timeouts, all_timeouts_initialized, Assert(), disable_alarm, find_active_timeout(), GetCurrentTimestamp(), i, DisableTimeoutParams::id, timeout_params::indicator, num_active_timeouts, remove_timeout_index(), and schedule_alarm().

Referenced by LockErrorCleanup(), and ProcSleep().

◆ enable_timeout()

static void enable_timeout ( TimeoutId  id,
TimestampTz  now,
TimestampTz  fin_time,
int  interval_in_ms 
)
static

Definition at line 158 of file timeout.c.

160 {
161  int i;
162 
163  /* Assert request is sane */
165  Assert(all_timeouts[id].timeout_handler != NULL);
166 
167  /*
168  * If this timeout was already active, momentarily disable it. We
169  * interpret the call as a directive to reschedule the timeout.
170  */
171  if (all_timeouts[id].active)
173 
174  /*
175  * Find out the index where to insert the new timeout. We sort by
176  * fin_time, and for equal fin_time by priority.
177  */
178  for (i = 0; i < num_active_timeouts; i++)
179  {
180  timeout_params *old_timeout = active_timeouts[i];
181 
182  if (fin_time < old_timeout->fin_time)
183  break;
184  if (fin_time == old_timeout->fin_time && id < old_timeout->index)
185  break;
186  }
187 
188  /*
189  * Mark the timeout active, and insert it into the active list.
190  */
191  all_timeouts[id].indicator = false;
193  all_timeouts[id].fin_time = fin_time;
194  all_timeouts[id].interval_in_ms = interval_in_ms;
195 
196  insert_timeout(id, i);
197 }
Datum now(PG_FUNCTION_ARGS)
Definition: timestamp.c:1538
Definition: type.h:90
int interval_in_ms
Definition: timeout.c:39
TimestampTz start_time
Definition: timeout.c:37
TimestampTz fin_time
Definition: timeout.c:38
static timeout_params *volatile active_timeouts[MAX_TIMEOUTS]
Definition: timeout.c:53
static void insert_timeout(TimeoutId id, int index)
Definition: timeout.c:114

References active_timeouts, all_timeouts, all_timeouts_initialized, Assert(), timeout_params::fin_time, find_active_timeout(), i, timeout_params::indicator, insert_timeout(), timeout_params::interval_in_ms, now(), num_active_timeouts, remove_timeout_index(), and timeout_params::start_time.

Referenced by enable_timeout_after(), enable_timeout_at(), enable_timeout_every(), enable_timeouts(), and handle_sig_alarm().

◆ enable_timeout_after()

void enable_timeout_after ( TimeoutId  id,
int  delay_ms 
)

Definition at line 564 of file timeout.c.

565 {
567  TimestampTz fin_time;
568 
569  /* Disable timeout interrupts for safety. */
570  disable_alarm();
571 
572  /* Queue the timeout at the appropriate time. */
574  fin_time = TimestampTzPlusMilliseconds(now, delay_ms);
575  enable_timeout(id, now, fin_time, 0);
576 
577  /* Set the timer interrupt. */
579 }
int64 TimestampTz
Definition: timestamp.h:39
static void enable_timeout(TimeoutId id, TimestampTz now, TimestampTz fin_time, int interval_in_ms)
Definition: timeout.c:158
#define TimestampTzPlusMilliseconds(tz, ms)
Definition: timestamp.h:56

References disable_alarm, enable_timeout(), GetCurrentTimestamp(), now(), schedule_alarm(), and TimestampTzPlusMilliseconds.

Referenced by BackendInitialize(), enable_statement_timeout(), PerformAuthentication(), PostgresMain(), ProcessInterrupts(), ProcSleep(), and start_xact_command().

◆ enable_timeout_at()

void enable_timeout_at ( TimeoutId  id,
TimestampTz  fin_time 
)

Definition at line 611 of file timeout.c.

612 {
614 
615  /* Disable timeout interrupts for safety. */
616  disable_alarm();
617 
618  /* Queue the timeout at the appropriate time. */
620  enable_timeout(id, now, fin_time, 0);
621 
622  /* Set the timer interrupt. */
624 }

References disable_alarm, enable_timeout(), GetCurrentTimestamp(), now(), and schedule_alarm().

◆ enable_timeout_every()

void enable_timeout_every ( TimeoutId  id,
TimestampTz  fin_time,
int  delay_ms 
)

Definition at line 588 of file timeout.c.

589 {
591 
592  /* Disable timeout interrupts for safety. */
593  disable_alarm();
594 
595  /* Queue the timeout at the appropriate time. */
597  enable_timeout(id, now, fin_time, delay_ms);
598 
599  /* Set the timer interrupt. */
601 }

References disable_alarm, enable_timeout(), GetCurrentTimestamp(), now(), and schedule_alarm().

Referenced by begin_startup_progress_phase().

◆ enable_timeouts()

void enable_timeouts ( const EnableTimeoutParams timeouts,
int  count 
)

Definition at line 634 of file timeout.c.

635 {
637  int i;
638 
639  /* Disable timeout interrupts for safety. */
640  disable_alarm();
641 
642  /* Queue the timeout(s) at the appropriate times. */
644 
645  for (i = 0; i < count; i++)
646  {
647  TimeoutId id = timeouts[i].id;
648  TimestampTz fin_time;
649 
650  switch (timeouts[i].type)
651  {
652  case TMPARAM_AFTER:
653  fin_time = TimestampTzPlusMilliseconds(now,
654  timeouts[i].delay_ms);
655  enable_timeout(id, now, fin_time, 0);
656  break;
657 
658  case TMPARAM_AT:
659  enable_timeout(id, now, timeouts[i].fin_time, 0);
660  break;
661 
662  case TMPARAM_EVERY:
663  fin_time = TimestampTzPlusMilliseconds(now,
664  timeouts[i].delay_ms);
665  enable_timeout(id, now, fin_time, timeouts[i].delay_ms);
666  break;
667 
668  default:
669  elog(ERROR, "unrecognized timeout type %d",
670  (int) timeouts[i].type);
671  break;
672  }
673  }
674 
675  /* Set the timer interrupt. */
677 }
#define ERROR
Definition: elog.h:33
#define elog(elevel,...)
Definition: elog.h:218
TimeoutId id
Definition: timeout.h:59
@ TMPARAM_AT
Definition: timeout.h:53
@ TMPARAM_EVERY
Definition: timeout.h:54
@ TMPARAM_AFTER
Definition: timeout.h:52

References disable_alarm, elog, enable_timeout(), ERROR, GetCurrentTimestamp(), i, EnableTimeoutParams::id, now(), schedule_alarm(), TimestampTzPlusMilliseconds, TMPARAM_AFTER, TMPARAM_AT, TMPARAM_EVERY, and generate_unaccent_rules::type.

Referenced by ProcSleep(), ResolveRecoveryConflictWithBufferPin(), and ResolveRecoveryConflictWithLock().

◆ find_active_timeout()

static int find_active_timeout ( TimeoutId  id)
static

Definition at line 96 of file timeout.c.

97 {
98  int i;
99 
100  for (i = 0; i < num_active_timeouts; i++)
101  {
102  if (active_timeouts[i]->index == id)
103  return i;
104  }
105 
106  return -1;
107 }

References active_timeouts, i, and num_active_timeouts.

Referenced by disable_timeout(), disable_timeouts(), and enable_timeout().

◆ get_timeout_active()

bool get_timeout_active ( TimeoutId  id)

Definition at line 784 of file timeout.c.

785 {
786  return all_timeouts[id].active;
787 }

References timeout_params::active, and all_timeouts.

Referenced by disable_statement_timeout(), enable_statement_timeout(), and start_xact_command().

◆ get_timeout_finish_time()

TimestampTz get_timeout_finish_time ( TimeoutId  id)

Definition at line 831 of file timeout.c.

832 {
833  return all_timeouts[id].fin_time;
834 }

References all_timeouts, and timeout_params::fin_time.

Referenced by ProcessInterrupts().

◆ get_timeout_indicator()

bool get_timeout_indicator ( TimeoutId  id,
bool  reset_indicator 
)

Definition at line 797 of file timeout.c.

798 {
799  if (all_timeouts[id].indicator)
800  {
801  if (reset_indicator)
802  all_timeouts[id].indicator = false;
803  return true;
804  }
805  return false;
806 }

References all_timeouts, and timeout_params::indicator.

Referenced by ProcessInterrupts().

◆ get_timeout_start_time()

TimestampTz get_timeout_start_time ( TimeoutId  id)

Definition at line 817 of file timeout.c.

818 {
819  return all_timeouts[id].start_time;
820 }

References all_timeouts, and timeout_params::start_time.

Referenced by ProcSleep().

◆ handle_sig_alarm()

static void handle_sig_alarm ( SIGNAL_ARGS  )
static

Definition at line 364 of file timeout.c.

365 {
366  int save_errno = errno;
367 
368  /*
369  * Bump the holdoff counter, to make sure nothing we call will process
370  * interrupts directly. No timeout handler should do that, but these
371  * failures are hard to debug, so better be sure.
372  */
373  HOLD_INTERRUPTS();
374 
375  /*
376  * SIGALRM is always cause for waking anything waiting on the process
377  * latch.
378  */
379  SetLatch(MyLatch);
380 
381  /*
382  * Always reset signal_pending, even if !alarm_enabled, since indeed no
383  * signal is now pending.
384  */
385  signal_pending = false;
386 
387  /*
388  * Fire any pending timeouts, but only if we're enabled to do so.
389  */
390  if (alarm_enabled)
391  {
392  /*
393  * Disable alarms, just in case this platform allows signal handlers
394  * to interrupt themselves. schedule_alarm() will re-enable if
395  * appropriate.
396  */
397  disable_alarm();
398 
399  if (num_active_timeouts > 0)
400  {
402 
403  /* While the first pending timeout has been reached ... */
404  while (num_active_timeouts > 0 &&
405  now >= active_timeouts[0]->fin_time)
406  {
407  timeout_params *this_timeout = active_timeouts[0];
408 
409  /* Remove it from the active list */
411 
412  /* Mark it as fired */
413  this_timeout->indicator = true;
414 
415  /* And call its handler function */
416  this_timeout->timeout_handler();
417 
418  /* If it should fire repeatedly, re-enable it. */
419  if (this_timeout->interval_in_ms > 0)
420  {
421  TimestampTz new_fin_time;
422 
423  /*
424  * To guard against drift, schedule the next instance of
425  * the timeout based on the intended firing time rather
426  * than the actual firing time. But if the timeout was so
427  * late that we missed an entire cycle, fall back to
428  * scheduling based on the actual firing time.
429  */
430  new_fin_time =
432  this_timeout->interval_in_ms);
433  if (new_fin_time < now)
434  new_fin_time =
436  this_timeout->interval_in_ms);
437  enable_timeout(this_timeout->index, now, new_fin_time,
438  this_timeout->interval_in_ms);
439  }
440 
441  /*
442  * The handler might not take negligible time (CheckDeadLock
443  * for instance isn't too cheap), so let's update our idea of
444  * "now" after each one.
445  */
447  }
448 
449  /* Done firing timeouts, so reschedule next interrupt if any */
451  }
452  }
453 
455 
456  errno = save_errno;
457 }
struct Latch * MyLatch
Definition: globals.c:58
void SetLatch(Latch *latch)
Definition: latch.c:591
#define RESUME_INTERRUPTS()
Definition: miscadmin.h:134
#define HOLD_INTERRUPTS()
Definition: miscadmin.h:132
timeout_handler_proc timeout_handler
Definition: timeout.c:35
TimeoutId index
Definition: timeout.c:28
static volatile sig_atomic_t alarm_enabled
Definition: timeout.c:67
static volatile sig_atomic_t signal_pending
Definition: timeout.c:78

References active_timeouts, alarm_enabled, disable_alarm, enable_timeout(), timeout_params::fin_time, GetCurrentTimestamp(), HOLD_INTERRUPTS, timeout_params::index, timeout_params::indicator, timeout_params::interval_in_ms, MyLatch, now(), num_active_timeouts, remove_timeout_index(), RESUME_INTERRUPTS, schedule_alarm(), SetLatch(), signal_pending, timeout_params::timeout_handler, and TimestampTzPlusMilliseconds.

Referenced by InitializeTimeouts().

◆ InitializeTimeouts()

void InitializeTimeouts ( void  )

Definition at line 474 of file timeout.c.

475 {
476  int i;
477 
478  /* Initialize, or re-initialize, all local state */
479  disable_alarm();
480 
482 
483  for (i = 0; i < MAX_TIMEOUTS; i++)
484  {
485  all_timeouts[i].index = i;
486  all_timeouts[i].active = false;
487  all_timeouts[i].indicator = false;
490  all_timeouts[i].fin_time = 0;
492  }
493 
495 
496  /* Now establish the signal handler */
498 }
pqsigfunc pqsignal(int signum, pqsigfunc handler)
Definition: signal.c:180
static void handle_sig_alarm(SIGNAL_ARGS)
Definition: timeout.c:364
#define SIGALRM
Definition: win32_port.h:173

References timeout_params::active, all_timeouts, all_timeouts_initialized, disable_alarm, timeout_params::fin_time, handle_sig_alarm(), i, timeout_params::index, timeout_params::indicator, timeout_params::interval_in_ms, MAX_TIMEOUTS, num_active_timeouts, pqsignal(), SIGALRM, timeout_params::start_time, and timeout_params::timeout_handler.

Referenced by AutoVacLauncherMain(), AutoVacWorkerMain(), BackendInitialize(), PostgresMain(), StartBackgroundWorker(), StartupProcessMain(), and WalSndSignals().

◆ insert_timeout()

static void insert_timeout ( TimeoutId  id,
int  index 
)
static

Definition at line 114 of file timeout.c.

115 {
116  int i;
117 
119  elog(FATAL, "timeout index %d out of range 0..%d", index,
121 
122  Assert(!all_timeouts[id].active);
123  all_timeouts[id].active = true;
124 
125  for (i = num_active_timeouts - 1; i >= index; i--)
127 
129 
131 }
#define FATAL
Definition: elog.h:35

References timeout_params::active, active_timeouts, all_timeouts, Assert(), elog, FATAL, i, and num_active_timeouts.

Referenced by enable_timeout().

◆ RegisterTimeout()

TimeoutId RegisterTimeout ( TimeoutId  id,
timeout_handler_proc  handler 
)

Definition at line 509 of file timeout.c.

510 {
512 
513  /* There's no need to disable the signal handler here. */
514 
515  if (id >= USER_TIMEOUT)
516  {
517  /* Allocate a user-defined timeout reason */
518  for (id = USER_TIMEOUT; id < MAX_TIMEOUTS; id++)
519  if (all_timeouts[id].timeout_handler == NULL)
520  break;
521  if (id >= MAX_TIMEOUTS)
522  ereport(FATAL,
523  (errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
524  errmsg("cannot add more timeout reasons")));
525  }
526 
527  Assert(all_timeouts[id].timeout_handler == NULL);
528 
529  all_timeouts[id].timeout_handler = handler;
530 
531  return id;
532 }
int errcode(int sqlerrcode)
Definition: elog.c:693
int errmsg(const char *fmt,...)
Definition: elog.c:904
#define ereport(elevel,...)
Definition: elog.h:143
@ USER_TIMEOUT
Definition: timeout.h:39

References all_timeouts, all_timeouts_initialized, Assert(), ereport, errcode(), errmsg(), FATAL, MAX_TIMEOUTS, timeout_params::timeout_handler, and USER_TIMEOUT.

Referenced by BackendInitialize(), InitPostgres(), StartupProcessMain(), and StartupXLOG().

◆ remove_timeout_index()

static void remove_timeout_index ( int  index)
static

Definition at line 137 of file timeout.c.

138 {
139  int i;
140 
142  elog(FATAL, "timeout index %d out of range 0..%d", index,
143  num_active_timeouts - 1);
144 
145  Assert(active_timeouts[index]->active);
146  active_timeouts[index]->active = false;
147 
148  for (i = index + 1; i < num_active_timeouts; i++)
150 
152 }

References timeout_params::active, active_timeouts, Assert(), elog, FATAL, i, and num_active_timeouts.

Referenced by disable_timeout(), disable_timeouts(), enable_timeout(), and handle_sig_alarm().

◆ reschedule_timeouts()

void reschedule_timeouts ( void  )

Definition at line 544 of file timeout.c.

545 {
546  /* For flexibility, allow this to be called before we're initialized. */
548  return;
549 
550  /* Disable timeout interrupts for safety. */
551  disable_alarm();
552 
553  /* Reschedule the interrupt, if any timeouts remain active. */
554  if (num_active_timeouts > 0)
556 }

References all_timeouts_initialized, disable_alarm, GetCurrentTimestamp(), num_active_timeouts, and schedule_alarm().

Referenced by AbortSubTransaction(), and AbortTransaction().

◆ schedule_alarm()

static void schedule_alarm ( TimestampTz  now)
static

Definition at line 210 of file timeout.c.

211 {
212  if (num_active_timeouts > 0)
213  {
214  struct itimerval timeval;
215  TimestampTz nearest_timeout;
216  long secs;
217  int usecs;
218 
219  MemSet(&timeval, 0, sizeof(struct itimerval));
220 
221  /*
222  * If we think there's a signal pending, but current time is more than
223  * 10ms past when the signal was due, then assume that the timeout
224  * request got lost somehow; clear signal_pending so that we'll reset
225  * the interrupt request below. (10ms corresponds to the worst-case
226  * timeout granularity on modern systems.) It won't hurt us if the
227  * interrupt does manage to fire between now and when we reach the
228  * setitimer() call.
229  */
230  if (signal_pending && now > signal_due_at + 10 * 1000)
231  signal_pending = false;
232 
233  /*
234  * Get the time remaining till the nearest pending timeout. If it is
235  * negative, assume that we somehow missed an interrupt, and clear
236  * signal_pending. This gives us another chance to recover if the
237  * kernel drops a timeout request for some reason.
238  */
239  nearest_timeout = active_timeouts[0]->fin_time;
240  if (now > nearest_timeout)
241  {
242  signal_pending = false;
243  /* force an interrupt as soon as possible */
244  secs = 0;
245  usecs = 1;
246  }
247  else
248  {
249  TimestampDifference(now, nearest_timeout,
250  &secs, &usecs);
251 
252  /*
253  * It's possible that the difference is less than a microsecond;
254  * ensure we don't cancel, rather than set, the interrupt.
255  */
256  if (secs == 0 && usecs == 0)
257  usecs = 1;
258  }
259 
260  timeval.it_value.tv_sec = secs;
261  timeval.it_value.tv_usec = usecs;
262 
263  /*
264  * We must enable the signal handler before calling setitimer(); if we
265  * did it in the other order, we'd have a race condition wherein the
266  * interrupt could occur before we can set alarm_enabled, so that the
267  * signal handler would fail to do anything.
268  *
269  * Because we didn't bother to disable the timer in disable_alarm(),
270  * it's possible that a previously-set interrupt will fire between
271  * enable_alarm() and setitimer(). This is safe, however. There are
272  * two possible outcomes:
273  *
274  * 1. The signal handler finds nothing to do (because the nearest
275  * timeout event is still in the future). It will re-set the timer
276  * and return. Then we'll overwrite the timer value with a new one.
277  * This will mean that the timer fires a little later than we
278  * intended, but only by the amount of time it takes for the signal
279  * handler to do nothing useful, which shouldn't be much.
280  *
281  * 2. The signal handler executes and removes one or more timeout
282  * events. When it returns, either the queue is now empty or the
283  * frontmost event is later than the one we looked at above. So we'll
284  * overwrite the timer value with one that is too soon (plus or minus
285  * the signal handler's execution time), causing a useless interrupt
286  * to occur. But the handler will then re-set the timer and
287  * everything will still work as expected.
288  *
289  * Since these cases are of very low probability (the window here
290  * being quite narrow), it's not worth adding cycles to the mainline
291  * code to prevent occasional wasted interrupts.
292  */
293  enable_alarm();
294 
295  /*
296  * If there is already an interrupt pending that's at or before the
297  * needed time, we need not do anything more. The signal handler will
298  * do the right thing in the first case, and re-schedule the interrupt
299  * for later in the second case. It might seem that the extra
300  * interrupt is wasted work, but it's not terribly much work, and this
301  * method has very significant advantages in the common use-case where
302  * we repeatedly set a timeout that we don't expect to reach and then
303  * cancel it. Instead of invoking setitimer() every time the timeout
304  * is set or canceled, we perform one interrupt and a re-scheduling
305  * setitimer() call at intervals roughly equal to the timeout delay.
306  * For example, with statement_timeout = 1s and a throughput of
307  * thousands of queries per second, this method requires an interrupt
308  * and setitimer() call roughly once a second, rather than thousands
309  * of setitimer() calls per second.
310  *
311  * Because of the possible passage of time between when we obtained
312  * "now" and when we reach setitimer(), the kernel's opinion of when
313  * to trigger the interrupt is likely to be a bit later than
314  * signal_due_at. That's fine, for the same reasons described above.
315  */
316  if (signal_pending && nearest_timeout >= signal_due_at)
317  return;
318 
319  /*
320  * As with calling enable_alarm(), we must set signal_pending *before*
321  * calling setitimer(); if we did it after, the signal handler could
322  * trigger before we set it, leaving us with a false opinion that a
323  * signal is still coming.
324  *
325  * Other race conditions involved with setting/checking signal_pending
326  * are okay, for the reasons described above. One additional point is
327  * that the signal handler could fire after we set signal_due_at, but
328  * still before the setitimer() call. Then the handler could
329  * overwrite signal_due_at with a value it computes, which will be the
330  * same as or perhaps later than what we just computed. After we
331  * perform setitimer(), the net effect would be that signal_due_at
332  * gives a time later than when the interrupt will really happen;
333  * which is a safe situation.
334  */
335  signal_due_at = nearest_timeout;
336  signal_pending = true;
337 
338  /* Set the alarm timer */
339  if (setitimer(ITIMER_REAL, &timeval, NULL) != 0)
340  {
341  /*
342  * Clearing signal_pending here is a bit pro forma, but not
343  * entirely so, since something in the FATAL exit path could try
344  * to use timeout facilities.
345  */
346  signal_pending = false;
347  elog(FATAL, "could not enable SIGALRM timer: %m");
348  }
349  }
350 }
void TimestampDifference(TimestampTz start_time, TimestampTz stop_time, long *secs, int *microsecs)
Definition: timestamp.c:1650
#define MemSet(start, val, len)
Definition: c.h:1008
#define enable_alarm()
Definition: timeout.c:70
static volatile TimestampTz signal_due_at
Definition: timeout.c:79
int setitimer(int which, const struct itimerval *value, struct itimerval *ovalue)
Definition: timer.c:86
#define ITIMER_REAL
Definition: win32_port.h:195

References active_timeouts, elog, enable_alarm, FATAL, timeout_params::fin_time, itimerval::it_value, ITIMER_REAL, MemSet, now(), num_active_timeouts, setitimer(), signal_due_at, signal_pending, and TimestampDifference().

Referenced by disable_timeout(), disable_timeouts(), enable_timeout_after(), enable_timeout_at(), enable_timeout_every(), enable_timeouts(), handle_sig_alarm(), and reschedule_timeouts().

Variable Documentation

◆ active_timeouts

◆ alarm_enabled

volatile sig_atomic_t alarm_enabled = false
static

Definition at line 67 of file timeout.c.

Referenced by handle_sig_alarm().

◆ all_timeouts

◆ all_timeouts_initialized

bool all_timeouts_initialized = false
static

◆ num_active_timeouts

◆ signal_due_at

volatile TimestampTz signal_due_at = 0
static

Definition at line 79 of file timeout.c.

Referenced by schedule_alarm().

◆ signal_pending

volatile sig_atomic_t signal_pending = false
static

Definition at line 78 of file timeout.c.

Referenced by handle_sig_alarm(), and schedule_alarm().