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         protected $cacheable = false; //Does this override getCachedWork() ?
  29
  30         /**
  31          * @param string $type The type of PoolCounter to use
  32          * @param string $key Key that identifies the queue this work is placed on
  33          */
  34         public function __construct( $type, $key ) {
  35                 $this->poolCounter = PoolCounter::factory( $type, $key );
  36         }
  37
  38         /**
  39          * Actually perform the work, caching it if needed
  40          * @return mixed work result or false
  41          */
  42         abstract public function doWork();
  43
  44         /**
  45          * Retrieve the work from cache
  46          * @return mixed work result or false
  47          */
  48         public function getCachedWork() {
  49                 return false;
  50         }
  51
  52         /**
  53          * A work not so good (eg. expired one) but better than an error
  54          * message.
  55          * @return mixed work result or false
  56          */
  57         public function fallback() {
  58                 return false;
  59         }
  60
  61         /**
  62          * Do something with the error, like showing it to the user.
  63          * @return bool
  64          */
  65         public function error( $status ) {
  66                 return false;
  67         }
  68
  69         /**
  70          * Log an error
  71          *
  72          * @param $status Status
  73          * @return void
  74          */
  75         public function logError( $status ) {
  76                 $key = $this->poolCounter->getKey();
  77
  78                 wfDebugLog( 'poolcounter', "Pool key '$key': "
  79                         . $status->getMessage()->inLanguage( 'en' )->useDatabase( false )->text() );
  80         }
  81
  82         /**
  83          * Get the result of the work (whatever it is), or the result of the error() function.
  84          * This returns the result of the first applicable method that returns a non-false value,
  85          * where the methods are checked in the following order:
  86          *   - a) doWork()       : Applies if the work is exclusive or no another process
  87          *                         is doing it, and on the condition that either this process
  88          *                         successfully entered the pool or the pool counter is down.
  89          *   - b) doCachedWork() : Applies if the work is cacheable and this blocked on another
  90          *                         process which finished the work.
  91          *   - c) fallback()     : Applies for all remaining cases.
  92          * If these all fall through (by returning false), then the result of error() is returned.
  93          *
  94          * @param $skipcache bool
  95          * @return mixed
  96          */
  97         public function execute( $skipcache = false ) {
  98                 if ( $this->cacheable && !$skipcache ) {
  99                         $status = $this->poolCounter->acquireForAnyone();
 100                 } else {
 101                         $status = $this->poolCounter->acquireForMe();
 102                 }
 103
 104                 if ( !$status->isOK() ) {
 105                         // Respond gracefully to complete server breakage: just log it and do the work
 106                         $this->logError( $status );
 107                         return $this->doWork();
 108                 }
 109
 110                 switch ( $status->value ) {
 111                         case PoolCounter::LOCKED:
 112                                 $result = $this->doWork();
 113                                 $this->poolCounter->release();
 114                                 return $result;
 115
 116                         case PoolCounter::DONE:
 117                                 $result = $this->getCachedWork();
 118                                 if ( $result === false ) {
 119                                         /* That someone else work didn't serve us.
 120                                          * Acquire the lock for me
 121                                          */
 122                                         return $this->execute( true );
 123                                 }
 124                                 return $result;
 125
 126                         case PoolCounter::QUEUE_FULL:
 127                         case PoolCounter::TIMEOUT:
 128                                 $result = $this->fallback();
 129
 130                                 if ( $result !== false ) {
 131                                         return $result;
 132                                 }
 133                                 /* no break */
 134
 135                         /* These two cases should never be hit... */
 136                         case PoolCounter::ERROR:
 137                         default:
 138                                 $errors = array(
 139                                         PoolCounter::QUEUE_FULL => 'pool-queuefull',
 140                                         PoolCounter::TIMEOUT => 'pool-timeout' );
 141
 142                                 $status = Status::newFatal( isset( $errors[$status->value] )
 143                                         ? $errors[$status->value]
 144                                         : 'pool-errorunknown' );
 145                                 $this->logError( $status );
 146                                 return $this->error( $status );
 147                 }
 148         }
 149 }
 150
 151 /**
 152  * Convenience class for dealing with PoolCounters using callbacks
 153  * @since 1.22
 154  */
 155 class PoolCounterWorkViaCallback extends PoolCounterWork {
 156         /** @var callable */
 157         protected $doWork;
 158         /** @var callable|null */
 159         protected $doCachedWork;
 160         /** @var callable|null */
 161         protected $fallback;
 162         /** @var callable|null */
 163         protected $error;
 164
 165         /**
 166          * Build a PoolCounterWork class from a type, key, and callback map.
 167          *
 168          * The callback map must at least have a callback for the 'doWork' method.
 169          * Additionally, callbacks can be provided for the 'doCachedWork', 'fallback',
 170          * and 'error' methods. Methods without callbacks will be no-ops that return false.
 171          * If a 'doCachedWork' callback is provided, then execute() may wait for any prior
 172          * process in the pool to finish and reuse its cached result.
 173          *
 174          * @param string $type
 175          * @param string $key
 176          * @param array $callbacks Map of callbacks
 177          * @throws MWException
 178          */
 179         public function __construct( $type, $key, array $callbacks ) {
 180                 parent::__construct( $type, $key );
 181                 foreach ( array( 'doWork', 'doCachedWork', 'fallback', 'error' ) as $name ) {
 182                         if ( isset( $callbacks[$name] ) ) {
 183                                 if ( !is_callable( $callbacks[$name] ) ) {
 184                                         throw new MWException( "Invalid callback provided for '$name' function." );
 185                                 }
 186                                 $this->$name = $callbacks[$name];
 187                         }
 188                 }
 189                 if ( !isset( $this->doWork ) ) {
 190                         throw new MWException( "No callback provided for 'doWork' function." );
 191                 }
 192                 $this->cacheable = isset( $this->doCachedWork );
 193         }
 194
 195         public function doWork() {
 196                 return call_user_func_array( $this->doWork, array() );
 197         }
 198
 199         public function getCachedWork() {
 200                 if ( $this->doCachedWork ) {
 201                         return call_user_func_array( $this->doCachedWork, array() );
 202                 }
 203                 return false;
 204         }
 205
 206         public function fallback() {
 207                 if ( $this->fallback ) {
 208                         return call_user_func_array( $this->fallback, array() );
 209                 }
 210                 return false;
 211         }
 212
 213         public function error( $status ) {
 214                 if ( $this->error ) {
 215                         return call_user_func_array( $this->error, array( $status ) );
 216                 }
 217                 return false;
 218         }
 219 }