From: Aaron Schulz <aschulz@wikimedia.org>
Date: Sun, 3 Feb 2019 02:13:17 +0000 (-0800)
Subject: objectcache: avoid duplicate set() calls with lockTSE when no value is in cache
X-Git-Tag: 1.34.0-rc.0~2952^2
X-Git-Url: http://git.cyclocoop.org/%28?a=commitdiff_plain;h=70bf85d4626;p=lhc%2Fweb%2Fwiklou.git

objectcache: avoid duplicate set() calls with lockTSE when no value is in cache

Each thread will still run the callback, but only one will save the value back

Bug: T203786
Change-Id: Idc4738aa005cc44ec0f1adc6dcf2e3f87d0c9480
---

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index 6e8d266e14..88f87f857e 100644
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -1334,7 +1334,8 @@ class WANObjectCache implements IExpiringStore, LoggerAwareInterface {
 			$this->setInterimValue( $key, $wrapped, $tempTTL );
 		}
 
-		if ( $valueIsCacheable ) {
+		// Save the value unless a mutex-winning thread is already expected to do that
+		if ( $valueIsCacheable && ( !$useMutex || $lockAcquired ) ) {
 			$setOpts['lockTSE'] = $lockTSE;
 			$setOpts['staleTTL'] = $staleTTL;
 			// Use best known "since" timestamp if not provided