includes/poolcounter/PoolCounterWork.php

   1 <?php
   2 /**
   3  * Provides of semaphore semantics for restricting the number
   4  * of workers that may be concurrently performing the same task.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License along
  17  * with this program; if not, write to the Free Software Foundation, Inc.,
  18  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  19  * http://www.gnu.org/copyleft/gpl.html
  20  *
  21  * @file
  22  */
  23
  24 /**
  25  * Class for dealing with PoolCounters using class members
  26  */
  27 abstract class PoolCounterWork {
  28         /** @var string */
  29         protected $type = 'generic';
  30         /** @var bool */
  31         protected $cacheable = false; // does this override getCachedWork() ?
  32
  33         /**
  34          * @param string $type The class of actions to limit concurrency for (task type)
  35          * @param string $key Key that identifies the queue this work is placed on
  36          */
  37         public function __construct( $type, $key ) {
  38                 $this->type = $type;
  39                 $this->poolCounter = PoolCounter::factory( $type, $key );
  40         }
  41
  42         /**
  43          * Actually perform the work, caching it if needed
  44          * @return mixed Work result or false
  45          */
  46         abstract public function doWork();
  47
  48         /**
  49          * Retrieve the work from cache
  50          * @return mixed Work result or false
  51          */
  52         public function getCachedWork() {
  53                 return false;
  54         }
  55
  56         /**
  57          * A work not so good (eg. expired one) but better than an error
  58          * message.
  59          * @return mixed Work result or false
  60          */
  61         public function fallback() {
  62                 return false;
  63         }
  64
  65         /**
  66          * Do something with the error, like showing it to the user.
  67          *
  68          * @param Status $status
  69          *
  70          * @return bool
  71          */
  72         public function error( $status ) {
  73                 return false;
  74         }
  75
  76         /**
  77          * Log an error
  78          *
  79          * @param Status $status
  80          * @return void
  81          */
  82         public function logError( $status ) {
  83                 $key = $this->poolCounter->getKey();
  84
  85                 wfDebugLog( 'poolcounter', "Pool key '$key' ({$this->type}): "
  86                         . $status->getMessage()->inLanguage( 'en' )->useDatabase( false )->text() );
  87         }
  88
  89         /**
  90          * Get the result of the work (whatever it is), or the result of the error() function.
  91          * This returns the result of the first applicable method that returns a non-false value,
  92          * where the methods are checked in the following order:
  93          *   - a) doWork()       : Applies if the work is exclusive or no another process
  94          *                         is doing it, and on the condition that either this process
  95          *                         successfully entered the pool or the pool counter is down.
  96          *   - b) doCachedWork() : Applies if the work is cacheable and this blocked on another
  97          *                         process which finished the work.
  98          *   - c) fallback()     : Applies for all remaining cases.
  99          * If these all fall through (by returning false), then the result of error() is returned.
 100          *
 101          * @param bool $skipcache
 102          * @return mixed
 103          */
 104         public function execute( $skipcache = false ) {
 105                 if ( $this->cacheable && !$skipcache ) {
 106                         $status = $this->poolCounter->acquireForAnyone();
 107                 } else {
 108                         $status = $this->poolCounter->acquireForMe();
 109                 }
 110
 111                 if ( !$status->isOK() ) {
 112                         // Respond gracefully to complete server breakage: just log it and do the work
 113                         $this->logError( $status );
 114                         return $this->doWork();
 115                 }
 116
 117                 switch ( $status->value ) {
 118                         case PoolCounter::LOCK_HELD:
 119                                 // Better to ignore nesting pool counter limits than to fail.
 120                                 // Assume that the outer pool limiting is reasonable enough.
 121                                 /* no break */
 122                         case PoolCounter::LOCKED:
 123                                 $result = $this->doWork();
 124                                 $this->poolCounter->release();
 125                                 return $result;
 126
 127                         case PoolCounter::DONE:
 128                                 $result = $this->getCachedWork();
 129                                 if ( $result === false ) {
 130                                         /* That someone else work didn't serve us.
 131                                          * Acquire the lock for me
 132                                          */
 133                                         return $this->execute( true );
 134                                 }
 135                                 return $result;
 136
 137                         case PoolCounter::QUEUE_FULL:
 138                         case PoolCounter::TIMEOUT:
 139                                 $result = $this->fallback();
 140
 141                                 if ( $result !== false ) {
 142                                         return $result;
 143                                 }
 144                                 /* no break */
 145
 146                         /* These two cases should never be hit... */
 147                         case PoolCounter::ERROR:
 148                         default:
 149                                 $errors = [
 150                                         PoolCounter::QUEUE_FULL => 'pool-queuefull',
 151                                         PoolCounter::TIMEOUT => 'pool-timeout' ];
 152
 153                                 $status = Status::newFatal( isset( $errors[$status->value] )
 154                                         ? $errors[$status->value]
 155                                         : 'pool-errorunknown' );
 156                                 $this->logError( $status );
 157                                 return $this->error( $status );
 158                 }
 159         }
 160 }