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Commitd069957

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Remove the option to service interrupts during PGSemaphoreLock().
The remaining caller (lwlocks) doesn't need that facility, and we planto remove ImmedidateInterruptOK entirely. That means that interruptscan't be serviced race-free and portably anyway, so there's littlereason for keeping the feature.Reviewed-By: Heikki Linnakangas
1 parent6753333 commitd069957

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5 files changed

+12
-63
lines changed

5 files changed

+12
-63
lines changed

‎src/backend/port/posix_sema.c

Lines changed: 2 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -236,22 +236,14 @@ PGSemaphoreReset(PGSemaphore sema)
236236
* Lock a semaphore (decrement count), blocking if count would be < 0
237237
*/
238238
void
239-
PGSemaphoreLock(PGSemaphoresema,boolinterruptOK)
239+
PGSemaphoreLock(PGSemaphoresema)
240240
{
241241
interrStatus;
242242

243-
/*
244-
* See notes in sysv_sema.c's implementation of PGSemaphoreLock. Just as
245-
* that code does for semop(), we handle both the case where sem_wait()
246-
* returns errno == EINTR after a signal, and the case where it just keeps
247-
* waiting.
248-
*/
243+
/* See notes in sysv_sema.c's implementation of PGSemaphoreLock. */
249244
do
250245
{
251-
ImmediateInterruptOK=interruptOK;
252-
CHECK_FOR_INTERRUPTS();
253246
errStatus=sem_wait(PG_SEM_REF(sema));
254-
ImmediateInterruptOK= false;
255247
}while (errStatus<0&&errno==EINTR);
256248

257249
if (errStatus<0)

‎src/backend/port/sysv_sema.c

Lines changed: 4 additions & 39 deletions
Original file line numberDiff line numberDiff line change
@@ -364,7 +364,7 @@ PGSemaphoreReset(PGSemaphore sema)
364364
* Lock a semaphore (decrement count), blocking if count would be < 0
365365
*/
366366
void
367-
PGSemaphoreLock(PGSemaphoresema,boolinterruptOK)
367+
PGSemaphoreLock(PGSemaphoresema)
368368
{
369369
interrStatus;
370370
structsembufsops;
@@ -378,48 +378,13 @@ PGSemaphoreLock(PGSemaphore sema, bool interruptOK)
378378
* from the operation prematurely because we were sent a signal. So we
379379
* try and lock the semaphore again.
380380
*
381-
* Each time around the loop, we check for a cancel/die interrupt. On
382-
* some platforms, if such an interrupt comes in while we are waiting, it
383-
* will cause the semop() call to exit with errno == EINTR, allowing us to
384-
* service the interrupt (if not in a critical section already) during the
385-
* next loop iteration.
386-
*
387-
* Once we acquire the lock, we do NOT check for an interrupt before
388-
* returning. The caller needs to be able to record ownership of the lock
389-
* before any interrupt can be accepted.
390-
*
391-
* There is a window of a few instructions between CHECK_FOR_INTERRUPTS
392-
* and entering the semop() call. If a cancel/die interrupt occurs in
393-
* that window, we would fail to notice it until after we acquire the lock
394-
* (or get another interrupt to escape the semop()). We can avoid this
395-
* problem by temporarily setting ImmediateInterruptOK to true before we
396-
* do CHECK_FOR_INTERRUPTS; then, a die() interrupt in this interval will
397-
* execute directly. However, there is a huge pitfall: there is another
398-
* window of a few instructions after the semop() before we are able to
399-
* reset ImmediateInterruptOK. If an interrupt occurs then, we'll lose
400-
* control, which means that the lock has been acquired but our caller did
401-
* not get a chance to record the fact. Therefore, we only set
402-
* ImmediateInterruptOK if the caller tells us it's OK to do so, ie, the
403-
* caller does not need to record acquiring the lock. (This is currently
404-
* true for lockmanager locks, since the process that granted us the lock
405-
* did all the necessary state updates. It's not true for SysV semaphores
406-
* used to implement LW locks or emulate spinlocks --- but the wait time
407-
* for such locks should not be very long, anyway.)
408-
*
409-
* On some platforms, signals marked SA_RESTART (which is most, for us)
410-
* will not interrupt the semop(); it will just keep waiting. Therefore
411-
* it's necessary for cancel/die interrupts to be serviced directly by the
412-
* signal handler. On these platforms the behavior is really the same
413-
* whether the signal arrives just before the semop() begins, or while it
414-
* is waiting. The loop on EINTR is thus important only for platforms
415-
* without SA_RESTART.
381+
* We used to check interrupts here, but that required servicing
382+
* interrupts directly from signal handlers. Which is hard to do safely
383+
* and portably.
416384
*/
417385
do
418386
{
419-
ImmediateInterruptOK=interruptOK;
420-
CHECK_FOR_INTERRUPTS();
421387
errStatus=semop(sema->semId,&sops,1);
422-
ImmediateInterruptOK= false;
423388
}while (errStatus<0&&errno==EINTR);
424389

425390
if (errStatus<0)

‎src/backend/port/win32_sema.c

Lines changed: 1 addition & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -116,13 +116,11 @@ PGSemaphoreReset(PGSemaphore sema)
116116
* Serve the interrupt if interruptOK is true.
117117
*/
118118
void
119-
PGSemaphoreLock(PGSemaphoresema,boolinterruptOK)
119+
PGSemaphoreLock(PGSemaphoresema)
120120
{
121121
HANDLEwh[2];
122122
booldone= false;
123123

124-
ImmediateInterruptOK=interruptOK;
125-
126124
/*
127125
* Note: pgwin32_signal_event should be first to ensure that it will be
128126
* reported when multiple events are set. We want to guarantee that
@@ -173,8 +171,6 @@ PGSemaphoreLock(PGSemaphore sema, bool interruptOK)
173171
break;
174172
}
175173
}
176-
177-
ImmediateInterruptOK= false;
178174
}
179175

180176
/*

‎src/backend/storage/lmgr/lwlock.c

Lines changed: 4 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -863,8 +863,7 @@ LWLockDequeueSelf(LWLock *lock)
863863
*/
864864
for (;;)
865865
{
866-
/* "false" means cannot accept cancel/die interrupt here. */
867-
PGSemaphoreLock(&MyProc->sem, false);
866+
PGSemaphoreLock(&MyProc->sem);
868867
if (!MyProc->lwWaiting)
869868
break;
870869
extraWaits++;
@@ -1034,8 +1033,7 @@ LWLockAcquireCommon(LWLock *lock, LWLockMode mode, uint64 *valptr, uint64 val)
10341033

10351034
for (;;)
10361035
{
1037-
/* "false" means cannot accept cancel/die interrupt here. */
1038-
PGSemaphoreLock(&proc->sem, false);
1036+
PGSemaphoreLock(&proc->sem);
10391037
if (!proc->lwWaiting)
10401038
break;
10411039
extraWaits++;
@@ -1195,8 +1193,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
11951193

11961194
for (;;)
11971195
{
1198-
/* "false" means cannot accept cancel/die interrupt here. */
1199-
PGSemaphoreLock(&proc->sem, false);
1196+
PGSemaphoreLock(&proc->sem);
12001197
if (!proc->lwWaiting)
12011198
break;
12021199
extraWaits++;
@@ -1397,8 +1394,7 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
13971394

13981395
for (;;)
13991396
{
1400-
/* "false" means cannot accept cancel/die interrupt here. */
1401-
PGSemaphoreLock(&proc->sem, false);
1397+
PGSemaphoreLock(&proc->sem);
14021398
if (!proc->lwWaiting)
14031399
break;
14041400
extraWaits++;

‎src/include/storage/pg_sema.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -72,7 +72,7 @@ extern void PGSemaphoreCreate(PGSemaphore sema);
7272
externvoidPGSemaphoreReset(PGSemaphoresema);
7373

7474
/* Lock a semaphore (decrement count), blocking if count would be < 0 */
75-
externvoidPGSemaphoreLock(PGSemaphoresema,boolinterruptOK);
75+
externvoidPGSemaphoreLock(PGSemaphoresema);
7676

7777
/* Unlock a semaphore (increment count) */
7878
externvoidPGSemaphoreUnlock(PGSemaphoresema);

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