includes/objectcache/BagOStuff.php

   1 <?php
   2 /**
   3  * Classes to cache objects in PHP accelerators, SQL database or DBA files
   4  *
   5  * Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
   6  * http://www.mediawiki.org/
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License along
  19  * with this program; if not, write to the Free Software Foundation, Inc.,
  20  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  21  * http://www.gnu.org/copyleft/gpl.html
  22  *
  23  * @file
  24  * @ingroup Cache
  25  */
  26
  27 /**
  28  * @defgroup Cache Cache
  29  */
  30
  31 /**
  32  * interface is intended to be more or less compatible with
  33  * the PHP memcached client.
  34  *
  35  * backends for local hash array and SQL table included:
  36  * <code>
  37  *   $bag = new HashBagOStuff();
  38  *   $bag = new SqlBagOStuff(); # connect to db first
  39  * </code>
  40  *
  41  * @ingroup Cache
  42  */
  43 abstract class BagOStuff {
  44         private $debugMode = false;
  45
  46         /**
  47          * @param $bool bool
  48          */
  49         public function setDebug( $bool ) {
  50                 $this->debugMode = $bool;
  51         }
  52
  53         /* *** THE GUTS OF THE OPERATION *** */
  54         /* Override these with functional things in subclasses */
  55
  56         /**
  57          * Get an item with the given key. Returns false if it does not exist.
  58          * @param $key string
  59          * @param $casToken[optional] mixed
  60          * @return mixed Returns false on failure
  61          */
  62         abstract public function get( $key, &$casToken = null );
  63
  64         /**
  65          * Set an item.
  66          * @param $key string
  67          * @param $value mixed
  68          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  69          * @return bool success
  70          */
  71         abstract public function set( $key, $value, $exptime = 0 );
  72
  73         /**
  74          * Check and set an item.
  75          * @param $casToken mixed
  76          * @param $key string
  77          * @param $value mixed
  78          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  79          * @return bool success
  80          */
  81         abstract public function cas( $casToken, $key, $value, $exptime = 0 );
  82
  83         /**
  84          * Delete an item.
  85          * @param $key string
  86          * @param int $time Amount of time to delay the operation (mostly memcached-specific)
  87          * @return bool True if the item was deleted or not found, false on failure
  88          */
  89         abstract public function delete( $key, $time = 0 );
  90
  91         /**
  92          * Merge changes into the existing cache value (possibly creating a new one).
  93          * The callback function returns the new value given the current value (possibly false),
  94          * and takes the arguments: (this BagOStuff object, cache key, current value).
  95          *
  96          * @param $key string
  97          * @param $callback closure Callback method to be executed
  98          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  99          * @param int $attempts The amount of times to attempt a merge in case of failure
 100          * @return bool success
 101          */
 102         public function merge( $key, closure $callback, $exptime = 0, $attempts = 10 ) {
 103                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 104         }
 105
 106         /**
 107          * @see BagOStuff::merge()
 108          *
 109          * @param $key string
 110          * @param $callback closure Callback method to be executed
 111          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 112          * @param int $attempts The amount of times to attempt a merge in case of failure
 113          * @return bool success
 114          */
 115         protected function mergeViaCas( $key, closure $callback, $exptime = 0, $attempts = 10 ) {
 116                 do {
 117                         $casToken = null; // passed by reference
 118                         $currentValue = $this->get( $key, $casToken ); // get the old value
 119                         $value = $callback( $this, $key, $currentValue ); // derive the new value
 120
 121                         if ( $value === false ) {
 122                                 $success = true; // do nothing
 123                         } elseif ( $currentValue === false ) {
 124                                 // Try to create the key, failing if it gets created in the meantime
 125                                 $success = $this->add( $key, $value, $exptime );
 126                         } else {
 127                                 // Try to update the key, failing if it gets changed in the meantime
 128                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 129                         }
 130                 } while ( !$success && --$attempts );
 131
 132                 return $success;
 133         }
 134
 135         /**
 136          * @see BagOStuff::merge()
 137          *
 138          * @param $key string
 139          * @param $callback closure Callback method to be executed
 140          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 141          * @param int $attempts The amount of times to attempt a merge in case of failure
 142          * @return bool success
 143          */
 144         protected function mergeViaLock( $key, closure $callback, $exptime = 0, $attempts = 10 ) {
 145                 if ( !$this->lock( $key, 60 ) ) {
 146                         return false;
 147                 }
 148
 149                 $currentValue = $this->get( $key ); // get the old value
 150                 $value = $callback( $this, $key, $currentValue ); // derive the new value
 151
 152                 if ( $value === false ) {
 153                         $success = true; // do nothing
 154                 } else {
 155                         $success = $this->set( $key, $value, $exptime ); // set the new value
 156                 }
 157
 158                 if ( !$this->unlock( $key ) ) {
 159                         // this should never happen
 160                         trigger_error( "Could not release lock for key '$key'." );
 161                 }
 162
 163                 return $success;
 164         }
 165
 166         /**
 167          * @param $key string
 168          * @param $timeout integer [optional]
 169          * @return bool success
 170          */
 171         public function lock( $key, $timeout = 60 ) {
 172                 $timestamp = microtime( true ); // starting UNIX timestamp
 173                 if ( $this->add( "{$key}:lock", 1, $timeout ) ) {
 174                         return true;
 175                 }
 176
 177                 $uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
 178                 $sleep = 2 * $uRTT; // rough time to do get()+set()
 179
 180                 $locked = false; // lock acquired
 181                 $attempts = 0; // failed attempts
 182                 do {
 183                         if ( ++$attempts >= 3 && $sleep <= 1e6 ) {
 184                                 // Exponentially back off after failed attempts to avoid network spam.
 185                                 // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 186                                 $sleep *= 2;
 187                         }
 188                         usleep( $sleep ); // back off
 189                         $locked = $this->add( "{$key}:lock", 1, $timeout );
 190                 } while ( !$locked );
 191
 192                 return $locked;
 193         }
 194
 195         /**
 196          * @param $key string
 197          * @return bool success
 198          */
 199         public function unlock( $key ) {
 200                 return $this->delete( "{$key}:lock" );
 201         }
 202
 203         /**
 204          * Delete all objects expiring before a certain date.
 205          * @param string $date The reference date in MW format
 206          * @param $progressCallback callback|bool Optional, a function which will be called
 207          *     regularly during long-running operations with the percentage progress
 208          *     as the first parameter.
 209          *
 210          * @return bool on success, false if unimplemented
 211          */
 212         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 213                 // stub
 214                 return false;
 215         }
 216
 217         /* *** Emulated functions *** */
 218
 219         /**
 220          * Get an associative array containing the item for each of the keys that have items.
 221          * @param array $keys List of strings
 222          * @return Array
 223          */
 224         public function getMulti( array $keys ) {
 225                 $res = array();
 226                 foreach ( $keys as $key ) {
 227                         $val = $this->get( $key );
 228                         if ( $val !== false ) {
 229                                 $res[$key] = $val;
 230                         }
 231                 }
 232                 return $res;
 233         }
 234
 235         /**
 236          * @param $key string
 237          * @param $value mixed
 238          * @param $exptime integer
 239          * @return bool success
 240          */
 241         public function add( $key, $value, $exptime = 0 ) {
 242                 if ( $this->get( $key ) === false ) {
 243                         return $this->set( $key, $value, $exptime );
 244                 }
 245                 return false; // key already set
 246         }
 247
 248         /**
 249          * @param $key string
 250          * @param $value mixed
 251          * @param $exptime int
 252          * @return bool success
 253          * @deprecated 1.23
 254          */
 255         public function replace( $key, $value, $exptime = 0 ) {
 256                 wfDeprecated( __METHOD__, '1.23' );
 257                 if ( $this->get( $key ) !== false ) {
 258                         return $this->set( $key, $value, $exptime );
 259                 }
 260                 return false; // key not already set
 261         }
 262
 263         /**
 264          * Increase stored value of $key by $value while preserving its TTL
 265          * @param string $key Key to increase
 266          * @param $value Integer: Value to add to $key (Default 1)
 267          * @return integer|bool New value or false on failure
 268          */
 269         public function incr( $key, $value = 1 ) {
 270                 if ( !$this->lock( $key ) ) {
 271                         return false;
 272                 }
 273                 $n = $this->get( $key );
 274                 if ( $this->isInteger( $n ) ) { // key exists?
 275                         $n += intval( $value );
 276                         $this->set( $key, max( 0, $n ) ); // exptime?
 277                 } else {
 278                         $n = false;
 279                 }
 280                 $this->unlock( $key );
 281
 282                 return $n;
 283         }
 284
 285         /**
 286          * Decrease stored value of $key by $value while preserving its TTL
 287          * @param $key String
 288          * @param $value Integer
 289          * @return integer
 290          */
 291         public function decr( $key, $value = 1 ) {
 292                 return $this->incr( $key, - $value );
 293         }
 294
 295         /**
 296          * @param $text string
 297          */
 298         public function debug( $text ) {
 299                 if ( $this->debugMode ) {
 300                         $class = get_class( $this );
 301                         wfDebug( "$class debug: $text\n" );
 302                 }
 303         }
 304
 305         /**
 306          * Convert an optionally relative time to an absolute time
 307          * @param $exptime integer
 308          * @return int
 309          */
 310         protected function convertExpiry( $exptime ) {
 311                 if ( ( $exptime != 0 ) && ( $exptime < 86400 * 3650 /* 10 years */ ) ) {
 312                         return time() + $exptime;
 313                 } else {
 314                         return $exptime;
 315                 }
 316         }
 317
 318         /**
 319          * Convert an optionally absolute expiry time to a relative time. If an
 320          * absolute time is specified which is in the past, use a short expiry time.
 321          *
 322          * @param $exptime integer
 323          * @return integer
 324          */
 325         protected function convertToRelative( $exptime ) {
 326                 if ( $exptime >= 86400 * 3650 /* 10 years */ ) {
 327                         $exptime -= time();
 328                         if ( $exptime <= 0 ) {
 329                                 $exptime = 1;
 330                         }
 331                         return $exptime;
 332                 } else {
 333                         return $exptime;
 334                 }
 335         }
 336
 337         /**
 338          * Check if a value is an integer
 339          *
 340          * @param $value mixed
 341          * @return bool
 342          */
 343         protected function isInteger( $value ) {
 344                 return ( is_int( $value ) || ctype_digit( $value ) );
 345         }
 346 }