From ada8fa08fc6cf5f199b6df935b4d0a730aaa4fec Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 10 May 2012 13:36:14 -0400 Subject: [PATCH] Fix Windows implementation of PGSemaphoreLock. The original coding failed to reset ImmediateInterruptOK before returning, which would potentially allow a subsequent query-cancel interrupt to be accepted at an unsafe point. This is a really nasty bug since it's so hard to predict the consequences, but they could be unpleasant. Also, ensure that signal handlers are serviced before this function returns, even if the semaphore is already set. This should make the behavior more like Unix. Back-patch to all supported versions. --- src/backend/port/win32_sema.c | 20 ++++++++++++-------- 1 file changed, 12 insertions(+), 8 deletions(-) diff --git a/src/backend/port/win32_sema.c b/src/backend/port/win32_sema.c index 320218a888..a093e9f163 100644 --- a/src/backend/port/win32_sema.c +++ b/src/backend/port/win32_sema.c @@ -121,8 +121,13 @@ PGSemaphoreLock(PGSemaphore sema, bool interruptOK) DWORD ret; HANDLE wh[2]; - wh[0] = *sema; - wh[1] = pgwin32_signal_event; + /* + * Note: pgwin32_signal_event should be first to ensure that it will be + * reported when multiple events are set. We want to guarantee that + * pending signals are serviced. + */ + wh[0] = pgwin32_signal_event; + wh[1] = *sema; /* * As in other implementations of PGSemaphoreLock, we need to check for @@ -135,20 +140,19 @@ PGSemaphoreLock(PGSemaphore sema, bool interruptOK) ImmediateInterruptOK = interruptOK; CHECK_FOR_INTERRUPTS(); - errno = 0; ret = WaitForMultipleObjectsEx(2, wh, FALSE, INFINITE, TRUE); if (ret == WAIT_OBJECT_0) - { - /* We got it! */ - return; - } - else if (ret == WAIT_OBJECT_0 + 1) { /* Signal event is set - we have a signal to deliver */ pgwin32_dispatch_queued_signals(); errno = EINTR; } + else if (ret == WAIT_OBJECT_0 + 1) + { + /* We got it! */ + errno = 0; + } else /* Otherwise we are in trouble */ errno = EIDRM;