1 files changed, 73 insertions, 42 deletions

diff --git a/includes/PoolCounter.php b/includes/PoolCounter.php
index 3851767f..182520e1 100644
--- a/includes/PoolCounter.php
+++ b/includes/PoolCounter.php
@@ -4,9 +4,14 @@
  *  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'.
+ * of the cpu of the pool. This is also known as 'Michael Jackson effect'
+ * since this effect triggered on the english wikipedia on the day Michael
+ * Jackson died, the biographical article got hit with several edits per
+ * minutes and hundreds of read hits.
+ *
  *  The PoolCounter provides semaphore semantics for restricting the number
  * of workers that may be concurrently performing such single task.
  *
@@ -16,15 +21,15 @@
 abstract class PoolCounter {
 	
 	/* Return codes */
-	const LOCKED = 1; 	/* Lock acquired */
+	const LOCKED   = 1; /* Lock acquired */
 	const RELEASED = 2; /* Lock released */
-	const DONE = 3;		/* Another one did the work for you */
+	const DONE     = 3; /* Another worker 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 */
+	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.
@@ -62,6 +67,11 @@ abstract class PoolCounter {
 	
 	/**
 	 * Create a Pool counter. This should only be called from the PoolWorks.
+	 *
+	 * @param $type
+	 * @param $key
+	 *
+	 * @return PoolCounter
 	 */
 	public static function factory( $type, $key ) {
 		global $wgPoolCounterConf;
@@ -83,18 +93,28 @@ abstract class PoolCounter {
 }
 
 class PoolCounter_Stub extends PoolCounter {
+
+	/**
+	 * @return Status
+	 */
 	function acquireForMe() {
 		return Status::newGood( PoolCounter::LOCKED );
 	}
 
+	/**
+	 * @return Status
+	 */
 	function acquireForAnyone() {
 		return Status::newGood( PoolCounter::LOCKED );
 	}
 
+	/**
+	 * @return Status
+	 */
 	function release() {
 		return Status::newGood( PoolCounter::RELEASED );
 	}
-	
+
 	public function __construct() {
 		/* No parameters needed */
 	}
@@ -134,6 +154,13 @@ abstract class PoolCounterWork {
 	function error( $status ) {	
 		return false;
 	}
+
+	/**
+	 * Log an error
+	 */
+	function logError( $status ) {
+		wfDebugLog( 'poolcounter', $status->getWikiText() );
+	}
 	
 	/**
 	 * Get the result of the work (whatever it is), or false.
@@ -144,43 +171,47 @@ abstract class PoolCounterWork {
 		} else {
 			$status = $this->poolCounter->acquireForMe();
 		}
-		
-		if ( $status->isOK() ) {
-			switch ( $status->value ) {
-				case PoolCounter::LOCKED:
-					$result = $this->doWork();
-					$this->poolCounter->release();
-					return $result;
+
+		if ( !$status->isOK() ) {
+			// Respond gracefully to complete server breakage: just log it and do the work
+			$this->logError( $status );
+			return $this->doWork();
+		}
+
+		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();
 				
-				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 );
-					}
+				if ( $result !== false ) {
 					return $result;
-					
-				case PoolCounter::QUEUE_FULL:
-				case PoolCounter::TIMEOUT:
-					$result = $this->fallback();
-					
-					if ( $result !== false ) {
-						return $result;
-					}
-					/* no break */
+				}
+				/* no break */
+			
+			/* These two cases should never be hit... */
+			case PoolCounter::ERROR:
+			default:
+				$errors = array( PoolCounter::QUEUE_FULL => 'pool-queuefull', PoolCounter::TIMEOUT => 'pool-timeout' );
 				
-				/* 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 */
-			}
+				$status = Status::newFatal( isset($errors[$status->value]) ? $errors[$status->value] : 'pool-errorunknown' );
+				$this->logError( $status );
+				return $this->error( $status );
 		}
-		return $this->error( $status );
 	}
 	
 	function __construct( $type, $key ) {