[FileBackend] Fixed writer-populater cache race condition.

* Set the keys to PURGED on purge. We already only treat array values
  in cache is valid. This means that if a process reads the file, it
  caches in the meantime, and then the process tries to cache the file,
  the stale version will not be cached.

Change-Id: I7eb7b4529f8cea44b0d68c9149db4bcf100ac9d2

diff --git a/includes/filerepo/backend/FileBackendStore.php b/includes/filerepo/backend/FileBackendStore.php
index f02724f..2080639 100644 (file)
--- a/includes/filerepo/backend/FileBackendStore.php
+++ b/includes/filerepo/backend/FileBackendStore.php
@@ -1358,16 +1358,17 @@ abstract class FileBackendStore extends FileBackend {
         * @param $val mixed Information to cache
         */
        final protected function setContainerCache( $container, $val ) {
-               $this->memCache->set( $this->containerCacheKey( $container ), $val, 14*86400 );
+               $this->memCache->add( $this->containerCacheKey( $container ), $val, 14*86400 );
        }
 
        /**
-        * Delete the cached info for a container
+        * Delete the cached info for a container.
+        * The cache key is salted for a while to prevent race conditions.
         *
         * @param $container string Resolved container name
         */
        final protected function deleteContainerCache( $container ) {
-               if ( !$this->memCache->delete( $this->containerCacheKey( $container ) ) ) {
+               if ( !$this->memCache->set( $this->containerCacheKey( $container ), 'PURGED', 300 ) ) {
                        trigger_error( "Unable to delete stat cache for container $container." );
                }
        }
@@ -1445,16 +1446,17 @@ abstract class FileBackendStore extends FileBackend {
         * @param $val mixed Information to cache
         */
        final protected function setFileCache( $path, $val ) {
-               $this->memCache->set( $this->fileCacheKey( $path ), $val, 7*86400 );
+               $this->memCache->add( $this->fileCacheKey( $path ), $val, 7*86400 );
        }
 
        /**
-        * Delete the cached stat info for a file path
+        * Delete the cached stat info for a file path.
+        * The cache key is salted for a while to prevent race conditions.
         *
         * @param $path string Storage path
         */
        final protected function deleteFileCache( $path ) {
-               if ( !$this->memCache->delete( $this->fileCacheKey( $path ) ) ) {
+               if ( !$this->memCache->set( $this->fileCacheKey( $path ), 'PURGED', 300 ) ) {
                        trigger_error( "Unable to delete stat cache for file $path." );
                }
        }