postgres.git / summary / log / commit / refs

commit    43b73d1a40463ff1fe7dee4d61a46a158629ab2b
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon Apr 04 15:13:17 2016 +0000

    Fix latent portability issue in pgwin32_dispatch_queued_signals().
    
    The first iteration of the signal-checking loop would compute sigmask(0)
    which expands to 1<<(-1) which is undefined behavior according to the
    C standard.  The lack of field reports of trouble suggest that it
    evaluates to 0 on all existing Windows compilers, but that's hardly
    something to rely on.  Since signal 0 isn't a queueable signal anyway,
    we can just make the loop iterate from 1 instead, and save a few cycles
    as well as avoiding the undefined behavior.
    
    In passing, avoid evaluating the volatile expression UNBLOCKED_SIGNAL_QUEUE
    twice in a row; there's no reason to waste cycles like that.
    
    Noted by Aleksander Alekseev, though this isn't his proposed fix.
    Back-patch to all supported branches.


 src/backend/port/win32/signal.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/backend/port/win32/signal.c b/src/backend/port/win32/signal.c
index 8b2d98141b5..3023b9340cc 100644
--- a/src/backend/port/win32/signal.c
+++ b/src/backend/port/win32/signal.c
@@ -33,6 +33,7 @@ HANDLE		pgwin32_initial_signal_pipe = INVALID_HANDLE_VALUE;
  */
 static CRITICAL_SECTION pg_signal_crit_sec;
 
+/* Note that array elements 0 are unused since they correspond to signal 0 */
 static pqsigfunc pg_signal_array[PG_SIGNAL_COUNT];
 static pqsigfunc pg_signal_defaults[PG_SIGNAL_COUNT];
 
@@ -105,15 +106,15 @@ pgwin32_signal_initialize(void)
 void
 pgwin32_dispatch_queued_signals(void)
 {
-	int			i;
+	int			exec_mask;
 
 	EnterCriticalSection(&pg_signal_crit_sec);
-	while (UNBLOCKED_SIGNAL_QUEUE())
+	while ((exec_mask = UNBLOCKED_SIGNAL_QUEUE()) != 0)
 	{
 		/* One or more unblocked signals queued for execution */
-		int			exec_mask = UNBLOCKED_SIGNAL_QUEUE();
+		int			i;
 
-		for (i = 0; i < PG_SIGNAL_COUNT; i++)
+		for (i = 1; i < PG_SIGNAL_COUNT; i++)
 		{
 			if (exec_mask & sigmask(i))
 			{


[parent: cbf4f6bb34fc]