diff options
Diffstat (limited to 'src/backend/port/sysv_sema.c')
| -rw-r--r-- | src/backend/port/sysv_sema.c | 19 |
1 files changed, 14 insertions, 5 deletions
diff --git a/src/backend/port/sysv_sema.c b/src/backend/port/sysv_sema.c index 876b9c6bbb0..54a1f7c93b3 100644 --- a/src/backend/port/sysv_sema.c +++ b/src/backend/port/sysv_sema.c @@ -8,7 +8,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/port/sysv_sema.c,v 1.22 2008/01/01 19:45:51 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/port/sysv_sema.c,v 1.23 2008/01/26 19:55:08 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -377,10 +377,11 @@ PGSemaphoreLock(PGSemaphore sema, bool interruptOK) * from the operation prematurely because we were sent a signal. So we * try and lock the semaphore again. * - * Each time around the loop, we check for a cancel/die interrupt. We - * assume that if such an interrupt comes in while we are waiting, it will - * cause the semop() call to exit with errno == EINTR, so that we will be - * able to service the interrupt (if not in a critical section already). + * Each time around the loop, we check for a cancel/die interrupt. On + * some platforms, if such an interrupt comes in while we are waiting, + * it will cause the semop() call to exit with errno == EINTR, allowing + * us to service the interrupt (if not in a critical section already) + * during the next loop iteration. * * Once we acquire the lock, we do NOT check for an interrupt before * returning. The caller needs to be able to record ownership of the lock @@ -403,6 +404,14 @@ PGSemaphoreLock(PGSemaphore sema, bool interruptOK) * did all the necessary state updates. It's not true for SysV semaphores * used to implement LW locks or emulate spinlocks --- but the wait time * for such locks should not be very long, anyway.) + * + * On some platforms, signals marked SA_RESTART (which is most, for us) + * will not interrupt the semop(); it will just keep waiting. Therefore + * it's necessary for cancel/die interrupts to be serviced directly by + * the signal handler. On these platforms the behavior is really the same + * whether the signal arrives just before the semop() begins, or while it + * is waiting. The loop on EINTR is thus important only for other types + * of interrupts. */ do { |