use Wikimedia\WaitConditionLoop;
/**
- * interface is intended to be more or less compatible with
- * the PHP memcached client.
+ * Class representing a cache/ephemeral data store
*
- * backends for local hash array and SQL table included:
- * @code
- * $bag = new HashBagOStuff();
- * $bag = new SqlBagOStuff(); # connect to db first
- * @endcode
+ * This interface is intended to be more or less compatible with the PHP memcached client.
+ *
+ * Instances of this class should be created with an intended access scope, such as:
+ * - a) A single PHP thread on a server (e.g. stored in a PHP variable)
+ * - b) A single application server (e.g. stored in APC or sqlite)
+ * - c) All application servers in datacenter (e.g. stored in memcached or mysql)
+ * - d) All application servers in all datacenters (e.g. stored via mcrouter or dynomite)
+ *
+ * Callers should use the proper factory methods that yield BagOStuff instances. Site admins
+ * should make sure the configuration for those factory methods matches their access scope.
+ * BagOStuff subclasses have widely varying levels of support for replication features.
+ *
+ * For any given instance, methods like lock(), unlock(), merge(), and set() with WRITE_SYNC
+ * should semantically operate over its entire access scope; any nodes/threads in that scope
+ * should serialize appropriately when using them. Likewise, a call to get() with READ_LATEST
+ * from one node in its access scope should reflect the prior changes of any other node its access
+ * scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
*
* @ingroup Cache
*/
/**
* Get an item with the given key
*
- * If the key includes a determistic input hash (e.g. the key can only have
+ * If the key includes a deterministic input hash (e.g. the key can only have
* the correct value) or complete staleness checks are handled by the caller
* (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
* This lets tiered backends know they can safely upgrade a cached value to
* @throws Exception
*/
protected function cas( $casToken, $key, $value, $exptime = 0 ) {
- throw new Exception( "CAS is not implemented in " . __CLASS__ );
+ if ( !$this->lock( $key, 0 ) ) {
+ return false; // non-blocking
+ }
+
+ $curCasToken = null; // passed by reference
+ $this->getWithToken( $key, $curCasToken, self::READ_LATEST );
+ if ( $casToken === $curCasToken ) {
+ $success = $this->set( $key, $value, $exptime );
+ } else {
+ $success = false; // mismatched or failed
+ }
+
+ $this->unlock( $key );
+
+ return $success;
}
/**
* Make a global cache key.
*
* @since 1.27
- * @param string $keys,... Key component (starting with a key collection name)
+ * @param string $class Key class
+ * @param string $component [optional] Key component (starting with a key collection name)
* @return string Colon-delimited list of $keyspace followed by escaped components of $args
*/
- public function makeGlobalKey() {
+ public function makeGlobalKey( $class, $component = null ) {
return $this->makeKeyInternal( 'global', func_get_args() );
}
* Make a cache key, scoped to this instance's keyspace.
*
* @since 1.27
- * @param string $keys,... Key component (starting with a key collection name)
+ * @param string $class Key class
+ * @param string $component [optional] Key component (starting with a key collection name)
* @return string Colon-delimited list of $keyspace followed by escaped components of $args
*/
- public function makeKey() {
+ public function makeKey( $class, $component = null ) {
return $this->makeKeyInternal( $this->keyspace, func_get_args() );
}