diff options
Diffstat (limited to 'src/backend/port/unix_latch.c')
| -rw-r--r-- | src/backend/port/unix_latch.c | 36 |
1 files changed, 19 insertions, 17 deletions
diff --git a/src/backend/port/unix_latch.c b/src/backend/port/unix_latch.c index e64282c2105..65b2fc56e03 100644 --- a/src/backend/port/unix_latch.c +++ b/src/backend/port/unix_latch.c @@ -183,6 +183,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock, { int result = 0; int rc; + #ifdef HAVE_POLL struct pollfd pfds[3]; int nfds; @@ -235,14 +236,15 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock, * * Note: we assume that the kernel calls involved in drainSelfPipe() * and SetLatch() will provide adequate synchronization on machines - * with weak memory ordering, so that we cannot miss seeing is_set - * if the signal byte is already in the pipe when we drain it. + * with weak memory ordering, so that we cannot miss seeing is_set if + * the signal byte is already in the pipe when we drain it. */ drainSelfPipe(); if ((wakeEvents & WL_LATCH_SET) && latch->is_set) { result |= WL_LATCH_SET; + /* * Leave loop immediately, avoid blocking again. We don't attempt * to report any other events that might also be satisfied. @@ -309,13 +311,14 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock, { result |= WL_SOCKET_WRITEABLE; } + /* * We expect a POLLHUP when the remote end is closed, but because we * don't expect the pipe to become readable or to have any errors * either, treat those as postmaster death, too. */ if ((wakeEvents & WL_POSTMASTER_DEATH) && - (pfds[nfds - 1].revents & (POLLHUP | POLLIN | POLLERR | POLLNVAL))) + (pfds[nfds - 1].revents & (POLLHUP | POLLIN | POLLERR | POLLNVAL))) { /* * According to the select(2) man page on Linux, select(2) may @@ -329,8 +332,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock, if (!PostmasterIsAlive()) result |= WL_POSTMASTER_DEATH; } - -#else /* !HAVE_POLL */ +#else /* !HAVE_POLL */ FD_ZERO(&input_mask); FD_ZERO(&output_mask); @@ -387,7 +389,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock, result |= WL_SOCKET_WRITEABLE; } if ((wakeEvents & WL_POSTMASTER_DEATH) && - FD_ISSET(postmaster_alive_fds[POSTMASTER_FD_WATCH], &input_mask)) + FD_ISSET(postmaster_alive_fds[POSTMASTER_FD_WATCH], &input_mask)) { /* * According to the select(2) man page on Linux, select(2) may @@ -401,7 +403,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock, if (!PostmasterIsAlive()) result |= WL_POSTMASTER_DEATH; } -#endif /* HAVE_POLL */ +#endif /* HAVE_POLL */ } while (result == 0); waiting = false; @@ -423,9 +425,9 @@ SetLatch(volatile Latch *latch) pid_t owner_pid; /* - * XXX there really ought to be a memory barrier operation right here, - * to ensure that any flag variables we might have changed get flushed - * to main memory before we check/set is_set. Without that, we have to + * XXX there really ought to be a memory barrier operation right here, to + * ensure that any flag variables we might have changed get flushed to + * main memory before we check/set is_set. Without that, we have to * require that callers provide their own synchronization for machines * with weak memory ordering (see latch.h). */ @@ -450,12 +452,12 @@ SetLatch(volatile Latch *latch) * Postgres; and PG database processes should handle excess SIGUSR1 * interrupts without a problem anyhow. * - * Another sort of race condition that's possible here is for a new process - * to own the latch immediately after we look, so we don't signal it. - * This is okay so long as all callers of ResetLatch/WaitLatch follow the - * standard coding convention of waiting at the bottom of their loops, - * not the top, so that they'll correctly process latch-setting events that - * happen before they enter the loop. + * Another sort of race condition that's possible here is for a new + * process to own the latch immediately after we look, so we don't signal + * it. This is okay so long as all callers of ResetLatch/WaitLatch follow + * the standard coding convention of waiting at the bottom of their loops, + * not the top, so that they'll correctly process latch-setting events + * that happen before they enter the loop. */ owner_pid = latch->owner_pid; if (owner_pid == 0) @@ -484,7 +486,7 @@ ResetLatch(volatile Latch *latch) /* * XXX there really ought to be a memory barrier operation right here, to * ensure that the write to is_set gets flushed to main memory before we - * examine any flag variables. Otherwise a concurrent SetLatch might + * examine any flag variables. Otherwise a concurrent SetLatch might * falsely conclude that it needn't signal us, even though we have missed * seeing some flag updates that SetLatch was supposed to inform us of. * For the moment, callers must supply their own synchronization of flag |