From: Aaron Schulz <aschulz@wikimedia.org>
Date: Tue, 10 Nov 2015 22:34:24 +0000 (-0800)
Subject: Avoid doNotifyQueueEmpty() race conditions for Redis
X-Git-Tag: 1.31.0-rc.0~8979^2~1
X-Git-Url: http://git.cyclocoop.org//%27%40script%40/%27?a=commitdiff_plain;h=ab2e1dae28f3b15e100e814544419f6719ef06f5;p=lhc%2Fweb%2Fwiklou.git

Avoid doNotifyQueueEmpty() race conditions for Redis

Previously, races could cause queues to be seen as empty
and ignored when they actually have jobs in them.

Change-Id: I6cdf5c1fbd33c9ed7982e5d2d494974b1d7e09fd
---

diff --git a/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php b/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php
index 6c49646b3b..f8a004040b 100644
--- a/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php
+++ b/includes/jobqueue/aggregator/JobQueueAggregatorRedis.php
@@ -59,7 +59,11 @@ class JobQueueAggregatorRedis extends JobQueueAggregator {
 			return false;
 		}
 		try {
-			$conn->hDel( $this->getReadyQueueKey(), $this->encQueueName( $type, $wiki ) );
+			// Make sure doNotifyQueueNonEmpty() takes precedence to avoid races
+			$conn->watch( $this->getReadyQueueKey() );
+			$conn->multi()
+				->hDel( $this->getReadyQueueKey(), $this->encQueueName( $type, $wiki ) )
+				->exec();
 
 			return true;
 		} catch ( RedisException $e ) {