From 9db190c7e736ec8d063187d4241b59feaf7dc2d1 Mon Sep 17 00:00:00 2001
From: Pierre Schmitz <pierre@archlinux.de>
Date: Wed, 22 Jun 2011 11:28:20 +0200
Subject: update to MediaWiki 1.17.0

---
 includes/PoolCounter.php | 203 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 164 insertions(+), 39 deletions(-)

(limited to 'includes/PoolCounter.php')

diff --git a/includes/PoolCounter.php b/includes/PoolCounter.php
index 2564fbc6..3851767f 100644
--- a/includes/PoolCounter.php
+++ b/includes/PoolCounter.php
@@ -1,6 +1,68 @@
 <?php
 
+/**
+ *  When you have many workers (threads/servers) giving service, and a 
+ * cached item expensive to produce expires, you may get several workers
+ * doing the job at the same time.
+ *  Given enough requests and the item expiring fast (non-cacheable, 
+ * lots of edits...) that single work can end up unfairly using most (all)
+ * of the cpu of the pool. This is also known as 'Michael Jackson effect'.
+ *  The PoolCounter provides semaphore semantics for restricting the number
+ * of workers that may be concurrently performing such single task.
+ *
+ *  By default PoolCounter_Stub is used, which provides no locking. You 
+ * can get a useful one in the PoolCounter extension.
+ */
 abstract class PoolCounter {
+	
+	/* Return codes */
+	const LOCKED = 1; 	/* Lock acquired */
+	const RELEASED = 2; /* Lock released */
+	const DONE = 3;		/* Another one did the work for you */
+	
+	const ERROR = -1;		/* Indeterminate error */
+	const NOT_LOCKED = -2;	/* Called release() with no lock held */
+	const QUEUE_FULL = -3;	/* There are already maxqueue workers on this lock */
+	const TIMEOUT = -4;		/* Timeout exceeded */
+	const LOCK_HELD = -5;	/* Cannot acquire another lock while you have one lock held */
+
+	/**
+	 * I want to do this task and I need to do it myself.
+	 * 
+	 * @return Locked/Error
+	 */
+	abstract function acquireForMe();
+
+	/**
+	 * I want to do this task, but if anyone else does it 
+	 * instead, it's also fine for me. I will read its cached data.
+	 * 
+	 * @return Locked/Done/Error
+	 */
+	abstract function acquireForAnyone();
+
+	/**
+	 * I have successfully finished my task.
+	 * Lets another one grab the lock, and returns the workers 
+	 * waiting on acquireForAnyone()
+	 * 
+	 * @return Released/NotLocked/Error
+	 */
+	abstract function release();
+	
+	/**
+	 *  $key: All workers with the same key share the lock.
+	 *  $workers: It wouldn't be a good idea to have more than this number of 
+	 * workers doing the task simultaneously.
+	 *  $maxqueue: If this number of workers are already working/waiting, 
+	 * fail instead of wait.
+	 *  $timeout: Maximum time in seconds to wait for the lock.
+	 */
+	protected $key, $workers, $maxqueue, $timeout;
+	
+	/**
+	 * Create a Pool counter. This should only be called from the PoolWorks.
+	 */
 	public static function factory( $type, $key ) {
 		global $wgPoolCounterConf;
 		if ( !isset( $wgPoolCounterConf[$type] ) ) {
@@ -8,57 +70,120 @@ abstract class PoolCounter {
 		}
 		$conf = $wgPoolCounterConf[$type];
 		$class = $conf['class'];
+		
 		return new $class( $conf, $type, $key );
 	}
-
-	abstract public function acquire();
-	abstract public function release();
-	abstract public function wait();
-
-	public function executeProtected( $mainCallback, $dirtyCallback = false ) {
-		$status = $this->acquire();
-		if ( !$status->isOK() ) {
-			return $status;
-		}
-		if ( !empty( $status->value['overload'] ) ) {
-			# Overloaded. Try a dirty cache entry.
-			if ( $dirtyCallback ) {
-				if ( call_user_func( $dirtyCallback ) ) {
-					$this->release();
-					return Status::newGood();
-				}
-			}
-
-			# Wait for a thread
-			$status = $this->wait();
-			if ( !$status->isOK() ) {
-				$this->release();
-				return $status;
-			}
-		}
-		# Call the main callback
-		call_user_func( $mainCallback );
-		return $this->release();
+	
+	protected function __construct( $conf, $type, $key ) {
+		$this->key = $key;
+		$this->workers  = $conf['workers'];
+		$this->maxqueue = $conf['maxqueue'];
+		$this->timeout  = $conf['timeout'];
 	}
 }
 
 class PoolCounter_Stub extends PoolCounter {
-	public function acquire() {
-		return Status::newGood();
+	function acquireForMe() {
+		return Status::newGood( PoolCounter::LOCKED );
 	}
 
-	public function release() {
-		return Status::newGood();
+	function acquireForAnyone() {
+		return Status::newGood( PoolCounter::LOCKED );
 	}
 
-	public function wait() {
-		return Status::newGood();
+	function release() {
+		return Status::newGood( PoolCounter::RELEASED );
 	}
-
-	public function executeProtected( $mainCallback, $dirtyCallback = false ) {
-		call_user_func( $mainCallback );
-		return Status::newGood();
+	
+	public function __construct() {
+		/* No parameters needed */
 	}
 }
 
+/**
+ * Handy class for dealing with PoolCounters using class members instead of callbacks.
+ */
+abstract class PoolCounterWork {
+	protected $cacheable = false; //Does this override getCachedWork() ?
+	
+	/**
+	 * Actually perform the work, caching it if needed.
+	 */
+	abstract function doWork();
 
+	/**
+	 * Retrieve the work from cache
+	 * @return mixed work result or false
+	 */
+	function getCachedWork() {
+		return false;
+	}
+
+	/**
+	 * A work not so good (eg. expired one) but better than an error 
+	 * message.
+	 * @return mixed work result or false
+	 */
+	function fallback() {
+		return false;
+	}
+	
+	/**
+	 * Do something with the error, like showing it to the user.
+	 */
+	function error( $status ) {	
+		return false;
+	}
+	
+	/**
+	 * Get the result of the work (whatever it is), or false.
+	 */
+	function execute( $skipcache = false ) {
+		if ( $this->cacheable && !$skipcache ) {
+			$status = $this->poolCounter->acquireForAnyone();
+		} else {
+			$status = $this->poolCounter->acquireForMe();
+		}
+		
+		if ( $status->isOK() ) {
+			switch ( $status->value ) {
+				case PoolCounter::LOCKED:
+					$result = $this->doWork();
+					$this->poolCounter->release();
+					return $result;
+				
+				case PoolCounter::DONE:
+					$result = $this->getCachedWork();
+					if ( $result === false ) {
+						/* That someone else work didn't serve us.
+						 * Acquire the lock for me
+						 */
+						return $this->execute( true );
+					}
+					return $result;
+					
+				case PoolCounter::QUEUE_FULL:
+				case PoolCounter::TIMEOUT:
+					$result = $this->fallback();
+					
+					if ( $result !== false ) {
+						return $result;
+					}
+					/* no break */
+				
+				/* These two cases should never be hit... */
+				case PoolCounter::ERROR:
+				default:
+					$errors = array( PoolCounter::QUEUE_FULL => 'pool-queuefull', PoolCounter::TIMEOUT => 'pool-timeout' );
+					
+					$status = Status::newFatal( isset($errors[$status->value]) ? $errors[$status->value] : 'pool-errorunknown' );
+					/* continue to the error */
+			}
+		}
+		return $this->error( $status );
+	}
+	
+	function __construct( $type, $key ) {
+		$this->poolCounter = PoolCounter::factory( $type, $key );
+	}
+}
-- 
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