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         /** @var PoolCounter */
  33         private $poolCounter;
  34
  35         /**
  36          * @param string $type The class of actions to limit concurrency for (task type)
  37          * @param string $key Key that identifies the queue this work is placed on
  38          */
  39         public function __construct( $type, $key ) {
  40                 $this->type = $type;
  41                 $this->poolCounter = PoolCounter::factory( $type, $key );
  42         }
  43
  44         /**
  45          * Actually perform the work, caching it if needed
  46          * @return mixed Work result or false
  47          */
  48         abstract public function doWork();
  49
  50         /**
  51          * Retrieve the work from cache
  52          * @return mixed Work result or false
  53          */
  54         public function getCachedWork() {
  55                 return false;
  56         }
  57
  58         /**
  59          * A work not so good (eg. expired one) but better than an error
  60          * message.
  61          * @return mixed Work result or false
  62          */
  63         public function fallback() {
  64                 return false;
  65         }
  66
  67         /**
  68          * Do something with the error, like showing it to the user.
  69          *
  70          * @param Status $status
  71          *
  72          * @return bool
  73          */
  74         public function error( $status ) {
  75                 return false;
  76         }
  77
  78         /**
  79          * Log an error
  80          *
  81          * @param Status $status
  82          * @return void
  83          */
  84         public function logError( $status ) {
  85                 $key = $this->poolCounter->getKey();
  86
  87                 wfDebugLog( 'poolcounter', "Pool key '$key' ({$this->type}): "
  88                         . $status->getMessage()->inLanguage( 'en' )->useDatabase( false )->text() );
  89         }
  90
  91         /**
  92          * Get the result of the work (whatever it is), or the result of the error() function.
  93          * This returns the result of the first applicable method that returns a non-false value,
  94          * where the methods are checked in the following order:
  95          *   - a) doWork()       : Applies if the work is exclusive or no another process
  96          *                         is doing it, and on the condition that either this process
  97          *                         successfully entered the pool or the pool counter is down.
  98          *   - b) doCachedWork() : Applies if the work is cacheable and this blocked on another
  99          *                         process which finished the work.
 100          *   - c) fallback()     : Applies for all remaining cases.
 101          * If these all fall through (by returning false), then the result of error() is returned.
 102          *
 103          * @param bool $skipcache
 104          * @return mixed
 105          */
 106         public function execute( $skipcache = false ) {
 107                 if ( $this->cacheable && !$skipcache ) {
 108                         $status = $this->poolCounter->acquireForAnyone();
 109                 } else {
 110                         $status = $this->poolCounter->acquireForMe();
 111                 }
 112
 113                 if ( !$status->isOK() ) {
 114                         // Respond gracefully to complete server breakage: just log it and do the work
 115                         $this->logError( $status );
 116                         return $this->doWork();
 117                 }
 118
 119                 switch ( $status->value ) {
 120                         case PoolCounter::LOCK_HELD:
 121                                 // Better to ignore nesting pool counter limits than to fail.
 122                                 // Assume that the outer pool limiting is reasonable enough.
 123                                 /* no break */
 124                         case PoolCounter::LOCKED:
 125                                 $result = $this->doWork();
 126                                 $this->poolCounter->release();
 127                                 return $result;
 128
 129                         case PoolCounter::DONE:
 130                                 $result = $this->getCachedWork();
 131                                 if ( $result === false ) {
 132                                         /* That someone else work didn't serve us.
 133                                          * Acquire the lock for me
 134                                          */
 135                                         return $this->execute( true );
 136                                 }
 137                                 return $result;
 138
 139                         case PoolCounter::QUEUE_FULL:
 140                         case PoolCounter::TIMEOUT:
 141                                 $result = $this->fallback();
 142
 143                                 if ( $result !== false ) {
 144                                         return $result;
 145                                 }
 146                                 /* no break */
 147
 148                         /* These two cases should never be hit... */
 149                         case PoolCounter::ERROR:
 150                         default:
 151                                 $errors = [
 152                                         PoolCounter::QUEUE_FULL => 'pool-queuefull',
 153                                         PoolCounter::TIMEOUT => 'pool-timeout' ];
 154
 155                                 $status = Status::newFatal( $errors[$status->value] ?? 'pool-errorunknown' );
 156                                 $this->logError( $status );
 157                                 return $this->error( $status );
 158                 }
 159         }
 160 }