From efd8f86283a85e03b77ff7b4136b0a59b81e7a1b Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Wed, 20 Apr 2016 08:34:55 -0700
Subject: [PATCH] Avoid ack() race condition in JobQueueRedis

The race would cause jobs to be be unclaimed but have
no actual job data, causing pop() to return false for
them.

Bug: T133089
Change-Id: Icc60388d4431ab7fa2ca2e46bbb0d212b2b94201
---
 includes/jobqueue/JobQueueRedis.php | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/includes/jobqueue/JobQueueRedis.php b/includes/jobqueue/JobQueueRedis.php
index d4a5334324..990248a064 100644
--- a/includes/jobqueue/JobQueueRedis.php
+++ b/includes/jobqueue/JobQueueRedis.php
@@ -393,12 +393,17 @@ LUA;
 			static $script =
 <<<LUA
 			local kClaimed, kAttempts, kData = unpack(KEYS)
-			local uuid = unpack(ARGV)
+			local id = unpack(ARGV)
 			-- Unmark the job as claimed
-			redis.call('zRem',kClaimed,uuid)
-			redis.call('hDel',kAttempts,uuid)
+			local removed = redis.call('zRem',kClaimed,id)
+			-- Check if the job was recycled
+			if removed == 0 then
+				return 0
+			end
+			-- Delete the retry data
+			redis.call('hDel',kAttempts,id)
 			-- Delete the job data itself
-			return redis.call('hDel',kData,uuid)
+			return redis.call('hDel',kData,id)
 LUA;
 			$res = $conn->luaEval( $script,
 				[
-- 
2.20.1