Followup r94541 (reverts of r94289 undiscussed core schema change and followups)...

[lhc/web/wiklou.git] / includes / PoolCounter.php

diff --git a/includes/PoolCounter.php b/includes/PoolCounter.php
index c24993e..182520e 100644 (file)
--- 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 */
        }
@@ -151,44 +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 );
                }
-               $this->logError( $status );
-               return $this->error( $status );
        }
        
        function __construct( $type, $key ) {