From cf54d68968e69df20342400f82cfd9f1eedf3711 Mon Sep 17 00:00:00 2001
From: Aaron Schulz <aschulz@wikimedia.org>
Date: Mon, 19 Feb 2018 03:50:29 -0800
Subject: [PATCH] Switch the sidebar cache to using checkKeys

The avoids the long delete() loop in MessageCache::replace()
and has better separation of concern.

Change-Id: I0acb0119058fa92fcafb52a5850f5dad4aaa94d2
---
 includes/cache/MessageCache.php | 33 +++++++++++++++------------------
 includes/skins/Skin.php         | 19 ++++++++++++++-----
 2 files changed, 29 insertions(+), 23 deletions(-)

diff --git a/includes/cache/MessageCache.php b/includes/cache/MessageCache.php
index d5ff6cbc9a..bbbb074337 100644
--- a/includes/cache/MessageCache.php
+++ b/includes/cache/MessageCache.php
@@ -300,7 +300,7 @@ class MessageCache {
 		}
 
 		if ( !$success ) {
-			$cacheKey = $this->clusterCache->makeKey( 'messages', $code ); # Key in memc for messages
+			$cacheKey = $this->clusterCache->makeKey( 'messages', $code );
 			# Try the global cache. If it is empty, try to acquire a lock. If
 			# the lock can't be acquired, wait for the other thread to finish
 			# and then try the global cache a second time.
@@ -622,19 +622,7 @@ class MessageCache {
 
 				// Relay the purge. Touching this check key expires cache contents
 				// and local cache (APC) validation hash across all datacenters.
-				$this->wanCache->touchCheckKey( $this->wanCache->makeKey( 'messages', $code ) );
-				// Also delete cached sidebar... just in case it is affected
-				// @TODO: shouldn't this be $code === $wgLanguageCode?
-				if ( $code === 'en' ) {
-					// Purge all language sidebars, e.g. on ?action=purge to the sidebar messages
-					$codes = array_keys( Language::fetchLanguageNames() );
-				} else {
-					// Purge only the sidebar for this language
-					$codes = [ $code ];
-				}
-				foreach ( $codes as $code ) {
-					$this->wanCache->delete( $this->wanCache->makeKey( 'sidebar', $code ) );
-				}
+				$this->wanCache->touchCheckKey( $this->getCheckKey( $code ) );
 
 				// Purge the message in the message blob store
 				$resourceloader = RequestContext::getMain()->getOutput()->getResourceLoader();
@@ -701,7 +689,7 @@ class MessageCache {
 		$value = $this->wanCache->get(
 			$this->wanCache->makeKey( 'messages', $code, 'hash', 'v1' ),
 			$curTTL,
-			[ $this->wanCache->makeKey( 'messages', $code ) ]
+			[ $this->getCheckKey( $code ) ]
 		);
 
 		if ( $value ) {
@@ -1199,13 +1187,14 @@ class MessageCache {
 	}
 
 	/**
-	 * Clear all stored messages. Mainly used after a mass rebuild.
+	 * Clear all stored messages in global and local cache
+	 *
+	 * Mainly used after a mass rebuild
 	 */
 	function clear() {
 		$langs = Language::fetchLanguageNames( null, 'mw' );
 		foreach ( array_keys( $langs ) as $code ) {
-			# Global and local caches
-			$this->wanCache->touchCheckKey( $this->wanCache->makeKey( 'messages', $code ) );
+			$this->wanCache->touchCheckKey( $this->getCheckKey( $code ) );
 		}
 
 		$this->mLoadedLanguages = [];
@@ -1283,6 +1272,14 @@ class MessageCache {
 		}
 	}
 
+	/**
+	 * @param string $code Language code
+	 * @return string WAN cache key usable as a "check key" against language page edits
+	 */
+	public function getCheckKey( $code ) {
+		return $this->wanCache->makeKey( 'messages', $code );
+	}
+
 	/**
 	 * @param Content|null $content Content or null if the message page does not exist
 	 * @return string|bool|null Returns false if $content is null and null on error
diff --git a/includes/skins/Skin.php b/includes/skins/Skin.php
index 4f271c7937..65a300afef 100644
--- a/includes/skins/Skin.php
+++ b/includes/skins/Skin.php
@@ -1253,7 +1253,7 @@ abstract class Skin extends ContextSource {
 	 *
 	 * @return array
 	 */
-	function buildSidebar() {
+	public function buildSidebar() {
 		global $wgEnableSidebarCache, $wgSidebarCacheExpiry;
 
 		$callback = function ( $old = null, &$ttl = null ) {
@@ -1267,13 +1267,22 @@ abstract class Skin extends ContextSource {
 			return $bar;
 		};
 
-		$cache = MediaWikiServices::getInstance()->getMainWANObjectCache();
+		$msgCache = MessageCache::singleton();
+		$wanCache = MediaWikiServices::getInstance()->getMainWANObjectCache();
+
 		$sidebar = $wgEnableSidebarCache
-			? $cache->getWithSetCallback(
-				$cache->makeKey( 'sidebar', $this->getLanguage()->getCode() ),
+			? $wanCache->getWithSetCallback(
+				$wanCache->makeKey( 'sidebar', $this->getLanguage()->getCode() ),
 				$wgSidebarCacheExpiry,
 				$callback,
-				[ 'lockTSE' => 30 ]
+				[
+					'checkKeys' => [
+						// Unless there is both no exact $code override nor an i18n definition
+						// in the the software, the only MediaWiki page to check is for $code.
+						$msgCache->getCheckKey( $this->getLanguage()->getCode() )
+					],
+					'lockTSE' => 30
+				]
 			)
 			: $callback();
 
-- 
2.20.1