MediaWiki 1.30.2

[autoinstallsdev/mediawiki.git] / includes / poolcounter / PoolCounterWork.php

diff --git a/includes/poolcounter/PoolCounterWork.php b/includes/poolcounter/PoolCounterWork.php
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+<?php
+/**
+ * Provides of semaphore semantics for restricting the number
+ * of workers that may be concurrently performing the same task.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+/**
+ * Class for dealing with PoolCounters using class members
+ */
+abstract class PoolCounterWork {
+       /** @var string */
+       protected $type = 'generic';
+       /** @var bool */
+       protected $cacheable = false; // does this override getCachedWork() ?
+
+       /**
+        * @param string $type The class of actions to limit concurrency for (task type)
+        * @param string $key Key that identifies the queue this work is placed on
+        */
+       public function __construct( $type, $key ) {
+               $this->type = $type;
+               $this->poolCounter = PoolCounter::factory( $type, $key );
+       }
+
+       /**
+        * Actually perform the work, caching it if needed
+        * @return mixed Work result or false
+        */
+       abstract public function doWork();
+
+       /**
+        * Retrieve the work from cache
+        * @return mixed Work result or false
+        */
+       public function getCachedWork() {
+               return false;
+       }
+
+       /**
+        * A work not so good (eg. expired one) but better than an error
+        * message.
+        * @return mixed Work result or false
+        */
+       public function fallback() {
+               return false;
+       }
+
+       /**
+        * Do something with the error, like showing it to the user.
+        *
+        * @param Status $status
+        *
+        * @return bool
+        */
+       public function error( $status ) {
+               return false;
+       }
+
+       /**
+        * Log an error
+        *
+        * @param Status $status
+        * @return void
+        */
+       public function logError( $status ) {
+               $key = $this->poolCounter->getKey();
+
+               wfDebugLog( 'poolcounter', "Pool key '$key' ({$this->type}): "
+                       . $status->getMessage()->inLanguage( 'en' )->useDatabase( false )->text() );
+       }
+
+       /**
+        * Get the result of the work (whatever it is), or the result of the error() function.
+        * This returns the result of the first applicable method that returns a non-false value,
+        * where the methods are checked in the following order:
+        *   - a) doWork()       : Applies if the work is exclusive or no another process
+        *                         is doing it, and on the condition that either this process
+        *                         successfully entered the pool or the pool counter is down.
+        *   - b) doCachedWork() : Applies if the work is cacheable and this blocked on another
+        *                         process which finished the work.
+        *   - c) fallback()     : Applies for all remaining cases.
+        * If these all fall through (by returning false), then the result of error() is returned.
+        *
+        * @param bool $skipcache
+        * @return mixed
+        */
+       public function execute( $skipcache = false ) {
+               if ( $this->cacheable && !$skipcache ) {
+                       $status = $this->poolCounter->acquireForAnyone();
+               } else {
+                       $status = $this->poolCounter->acquireForMe();
+               }
+
+               if ( !$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::LOCK_HELD:
+                               // Better to ignore nesting pool counter limits than to fail.
+                               // Assume that the outer pool limiting is reasonable enough.
+                               /* no break */
+                       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 = [
+                                       PoolCounter::QUEUE_FULL => 'pool-queuefull',
+                                       PoolCounter::TIMEOUT => 'pool-timeout' ];
+
+                               $status = Status::newFatal( isset( $errors[$status->value] )
+                                       ? $errors[$status->value]
+                                       : 'pool-errorunknown' );
+                               $this->logError( $status );
+                               return $this->error( $status );
+               }
+       }
+}