From a64ca63e59c11d8fe6db24eee3d82b61db7c2c83 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 15 Jun 2013 16:22:29 -0400
Subject: [PATCH] Use WaitLatch, not pg_usleep, for delaying in pg_sleep().
This avoids platform-dependent behavior wherein pg_sleep() might fail to be
interrupted by statement timeout, query cancel, SIGTERM, etc. Also, since
there's no reason to wake up once a second any more, we can reduce the
power consumption of a sleeping backend a tad.
Back-patch to 9.3, since use of SA_RESTART for SIGALRM makes this a bigger
issue than it used to be.
---
src/backend/utils/adt/misc.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)
diff --git a/src/backend/utils/adt/misc.c b/src/backend/utils/adt/misc.c
index bf06ec048ff..aecdcd056cd 100644
--- a/src/backend/utils/adt/misc.c
+++ b/src/backend/utils/adt/misc.c
@@ -384,16 +384,16 @@ pg_sleep(PG_FUNCTION_ARGS)
float8 endtime;
/*
- * We break the requested sleep into segments of no more than 1 second, to
- * put an upper bound on how long it will take us to respond to a cancel
- * or die interrupt. (Note that pg_usleep is interruptible by signals on
- * some platforms but not others.) Also, this method avoids exposing
- * pg_usleep's upper bound on allowed delays.
+ * We sleep using WaitLatch, to ensure that we'll wake up promptly if an
+ * important signal (such as SIGALRM or SIGINT) arrives. Because
+ * WaitLatch's upper limit of delay is INT_MAX milliseconds, and the user
+ * might ask for more than that, we sleep for at most 10 minutes and then
+ * loop.
*
* By computing the intended stop time initially, we avoid accumulation of
* extra delay across multiple sleeps. This also ensures we won't delay
- * less than the specified time if pg_usleep is interrupted by other
- * signals such as SIGHUP.
+ * less than the specified time when WaitLatch is terminated early by a
+ * non-query-cancelling signal such as SIGHUP.
*/
#ifdef HAVE_INT64_TIMESTAMP
@@ -407,15 +407,22 @@ pg_sleep(PG_FUNCTION_ARGS)
for (;;)
{
float8 delay;
+ long delay_ms;
CHECK_FOR_INTERRUPTS();
+
delay = endtime - GetNowFloat();
- if (delay >= 1.0)
- pg_usleep(1000000L);
+ if (delay >= 600.0)
+ delay_ms = 600000;
else if (delay > 0.0)
- pg_usleep((long) ceil(delay * 1000000.0));
+ delay_ms = (long) ceil(delay * 1000.0);
else
break;
+
+ (void) WaitLatch(&MyProc->procLatch,
+ WL_LATCH_SET | WL_TIMEOUT,
+ delay_ms);
+ ResetLatch(&MyProc->procLatch);
}
PG_RETURN_VOID();
--
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