resourceloader: Limit module_deps write lock to unique index

Follows-up 1d15085bb3.

The column has a unique index for module name and skin/language pair.
Previously the write lock was on module name, which meant that
shortly after deployment, the following happens:

* Files change on disk.
* (1-5min pass)
* First startup module request after 5min http-cache expires. Detects
  one or more changes and updates the version hash of that module.
* Web client subsequently requests this module (if used on that page).
  The first time that request comes in, it's a varnish cache miss
  and will make RL load all files from disk related to that module
  and update the cache index in the module_deps table. At this point
  most popular skin/lang pairs fail, except one. As a result, the
  other rows remain stale.
* (7-30 days varnish expiry pass OR another change to the module deploys)
* Web client requests this module and tries to update its skin/lang pair
  for that module.

One simple change in January 2016 changes jquery.tablesorter to load
a PNG file instead of a GIF file. Now, over a year later, there are
still a dozen skin/lang pairs in enwiki.module_deps with stale data,
which is causing various suble bugs, as well as filesystem calls for
files that don't exist.

Ref T113916 (refactor module_deps).
Ref T158105 (stale cache bug).

Bug: T158105
Change-Id: Ib6c024bfa8d35ce2d622ba4242291daedb507d5e

diff --git a/includes/resourceloader/ResourceLoaderModule.php b/includes/resourceloader/ResourceLoaderModule.php
index fd74a82..71e5939 100644 (file)
--- a/includes/resourceloader/ResourceLoaderModule.php
+++ b/includes/resourceloader/ResourceLoaderModule.php
@@ -468,14 +468,14 @@ abstract class ResourceLoaderModule implements LoggerAwareInterface {
                try {
                        // If the list has been modified since last time we cached it, update the cache
                        if ( $localFileRefs !== $this->getFileDependencies( $context ) ) {
+                               $vary = $context->getSkin() . '|' . $context->getLanguage();
                                $cache = ObjectCache::getLocalClusterInstance();
-                               $key = $cache->makeKey( __METHOD__, $this->getName() );
+                               $key = $cache->makeKey( __METHOD__, $this->getName(), $vary );
                                $scopeLock = $cache->getScopedLock( $key, 0 );
                                if ( !$scopeLock ) {
                                        return; // T124649; avoid write slams
                                }
 
-                               $vary = $context->getSkin() . '|' . $context->getLanguage();
                                // Use relative paths to avoid ghost entries when $IP changes (T111481)
                                $deps = FormatJson::encode( self::getRelativePaths( $localFileRefs ) );
                                $dbw = wfGetDB( DB_MASTER );