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  * https://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         protected $lastError = self::ERR_NONE;
  47
  48         /** Possible values for getLastError() */
  49         const ERR_NONE        = 0; // no error
  50         const ERR_NO_RESPONSE = 1; // no response
  51         const ERR_UNREACHABLE = 2; // can't connect
  52         const ERR_UNEXPECTED  = 3; // response gave some error
  53
  54         /**
  55          * @param bool $bool
  56          */
  57         public function setDebug( $bool ) {
  58                 $this->debugMode = $bool;
  59         }
  60
  61         /* *** THE GUTS OF THE OPERATION *** */
  62         /* Override these with functional things in subclasses */
  63
  64         /**
  65          * Get an item with the given key. Returns false if it does not exist.
  66          * @param string $key
  67          * @param mixed $casToken [optional]
  68          * @return mixed Returns false on failure
  69          */
  70         abstract public function get( $key, &$casToken = null );
  71
  72         /**
  73          * Set an item.
  74          * @param string $key
  75          * @param mixed $value
  76          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  77          * @return bool Success
  78          */
  79         abstract public function set( $key, $value, $exptime = 0 );
  80
  81         /**
  82          * Check and set an item.
  83          * @param mixed $casToken
  84          * @param string $key
  85          * @param mixed $value
  86          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  87          * @return bool Success
  88          */
  89         abstract public function cas( $casToken, $key, $value, $exptime = 0 );
  90
  91         /**
  92          * Delete an item.
  93          * @param string $key
  94          * @param int $time Amount of time to delay the operation (mostly memcached-specific)
  95          * @return bool True if the item was deleted or not found, false on failure
  96          */
  97         abstract public function delete( $key, $time = 0 );
  98
  99         /**
 100          * Merge changes into the existing cache value (possibly creating a new one).
 101          * The callback function returns the new value given the current value (possibly false),
 102          * and takes the arguments: (this BagOStuff object, cache key, current value).
 103          *
 104          * @param string $key
 105          * @param Closure $callback Callback method to be executed
 106          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 107          * @param int $attempts The amount of times to attempt a merge in case of failure
 108          * @return bool Success
 109          */
 110         public function merge( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 111                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 112         }
 113
 114         /**
 115          * @see BagOStuff::merge()
 116          *
 117          * @param string $key
 118          * @param Closure $callback Callback method to be executed
 119          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 120          * @param int $attempts The amount of times to attempt a merge in case of failure
 121          * @return bool Success
 122          */
 123         protected function mergeViaCas( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 124                 do {
 125                         $casToken = null; // passed by reference
 126                         $currentValue = $this->get( $key, $casToken ); // get the old value
 127                         $value = $callback( $this, $key, $currentValue ); // derive the new value
 128
 129                         if ( $value === false ) {
 130                                 $success = true; // do nothing
 131                         } elseif ( $currentValue === false ) {
 132                                 // Try to create the key, failing if it gets created in the meantime
 133                                 $success = $this->add( $key, $value, $exptime );
 134                         } else {
 135                                 // Try to update the key, failing if it gets changed in the meantime
 136                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 137                         }
 138                 } while ( !$success && --$attempts );
 139
 140                 return $success;
 141         }
 142
 143         /**
 144          * @see BagOStuff::merge()
 145          *
 146          * @param string $key
 147          * @param Closure $callback Callback method to be executed
 148          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 149          * @param int $attempts The amount of times to attempt a merge in case of failure
 150          * @return bool Success
 151          */
 152         protected function mergeViaLock( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 153                 if ( !$this->lock( $key, 6 ) ) {
 154                         return false;
 155                 }
 156
 157                 $currentValue = $this->get( $key ); // get the old value
 158                 $value = $callback( $this, $key, $currentValue ); // derive the new value
 159
 160                 if ( $value === false ) {
 161                         $success = true; // do nothing
 162                 } else {
 163                         $success = $this->set( $key, $value, $exptime ); // set the new value
 164                 }
 165
 166                 if ( !$this->unlock( $key ) ) {
 167                         // this should never happen
 168                         trigger_error( "Could not release lock for key '$key'." );
 169                 }
 170
 171                 return $success;
 172         }
 173
 174         /**
 175          * @param string $key
 176          * @param int $timeout [optional]
 177          * @return bool Success
 178          */
 179         public function lock( $key, $timeout = 6 ) {
 180                 $this->clearLastError();
 181                 $timestamp = microtime( true ); // starting UNIX timestamp
 182                 if ( $this->add( "{$key}:lock", 1, $timeout ) ) {
 183                         return true;
 184                 } elseif ( $this->getLastError() ) {
 185                         return false;
 186                 }
 187
 188                 $uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
 189                 $sleep = 2 * $uRTT; // rough time to do get()+set()
 190
 191                 $locked = false; // lock acquired
 192                 $attempts = 0; // failed attempts
 193                 do {
 194                         if ( ++$attempts >= 3 && $sleep <= 1e6 ) {
 195                                 // Exponentially back off after failed attempts to avoid network spam.
 196                                 // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 197                                 $sleep *= 2;
 198                         }
 199                         usleep( $sleep ); // back off
 200                         $this->clearLastError();
 201                         $locked = $this->add( "{$key}:lock", 1, $timeout );
 202                         if ( $this->getLastError() ) {
 203                                 return false;
 204                         }
 205                 } while ( !$locked );
 206
 207                 return $locked;
 208         }
 209
 210         /**
 211          * @param string $key
 212          * @return bool Success
 213          */
 214         public function unlock( $key ) {
 215                 return $this->delete( "{$key}:lock" );
 216         }
 217
 218         /**
 219          * Delete all objects expiring before a certain date.
 220          * @param string $date The reference date in MW format
 221          * @param callable|bool $progressCallback Optional, a function which will be called
 222          *     regularly during long-running operations with the percentage progress
 223          *     as the first parameter.
 224          *
 225          * @return bool Success, false if unimplemented
 226          */
 227         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 228                 // stub
 229                 return false;
 230         }
 231
 232         /* *** Emulated functions *** */
 233
 234         /**
 235          * Get an associative array containing the item for each of the keys that have items.
 236          * @param array $keys List of strings
 237          * @return array
 238          */
 239         public function getMulti( array $keys ) {
 240                 $res = array();
 241                 foreach ( $keys as $key ) {
 242                         $val = $this->get( $key );
 243                         if ( $val !== false ) {
 244                                 $res[$key] = $val;
 245                         }
 246                 }
 247                 return $res;
 248         }
 249
 250         /**
 251          * @param string $key
 252          * @param mixed $value
 253          * @param int $exptime
 254          * @return bool Success
 255          */
 256         public function add( $key, $value, $exptime = 0 ) {
 257                 if ( $this->get( $key ) === false ) {
 258                         return $this->set( $key, $value, $exptime );
 259                 }
 260                 return false; // key already set
 261         }
 262
 263         /**
 264          * @param string $key
 265          * @param mixed $value
 266          * @param int $exptime
 267          * @return bool Success
 268          * @deprecated since 1.23
 269          */
 270         public function replace( $key, $value, $exptime = 0 ) {
 271                 wfDeprecated( __METHOD__, '1.23' );
 272                 if ( $this->get( $key ) !== false ) {
 273                         return $this->set( $key, $value, $exptime );
 274                 }
 275                 return false; // key not already set
 276         }
 277
 278         /**
 279          * Increase stored value of $key by $value while preserving its TTL
 280          * @param string $key Key to increase
 281          * @param int $value Value to add to $key (Default 1)
 282          * @return int|bool New value or false on failure
 283          */
 284         public function incr( $key, $value = 1 ) {
 285                 if ( !$this->lock( $key ) ) {
 286                         return false;
 287                 }
 288                 $n = $this->get( $key );
 289                 if ( $this->isInteger( $n ) ) { // key exists?
 290                         $n += intval( $value );
 291                         $this->set( $key, max( 0, $n ) ); // exptime?
 292                 } else {
 293                         $n = false;
 294                 }
 295                 $this->unlock( $key );
 296
 297                 return $n;
 298         }
 299
 300         /**
 301          * Decrease stored value of $key by $value while preserving its TTL
 302          * @param string $key
 303          * @param int $value
 304          * @return int
 305          */
 306         public function decr( $key, $value = 1 ) {
 307                 return $this->incr( $key, - $value );
 308         }
 309
 310         /**
 311          * Increase stored value of $key by $value while preserving its TTL
 312          *
 313          * This will create the key with value $init and TTL $ttl if not present
 314          *
 315          * @param string $key
 316          * @param integer $ttl
 317          * @param integer $value
 318          * @param integer $init
 319          * @return bool
 320          * @since 1.24
 321          */
 322         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 323                 return $this->incr( $key, $value ) ||
 324                         $this->add( $key, $init, $ttl ) || $this->incr( $key, $value );
 325         }
 326
 327         /**
 328          * Get the "last error" registered; clearLastError() should be called manually
 329          * @return int ERR_* constant for the "last error" registry
 330          * @since 1.23
 331          */
 332         public function getLastError() {
 333                 return $this->lastError;
 334         }
 335
 336         /**
 337          * Clear the "last error" registry
 338          * @since 1.23
 339          */
 340         public function clearLastError() {
 341                 $this->lastError = self::ERR_NONE;
 342         }
 343
 344         /**
 345          * Set the "last error" registry
 346          * @param int $err ERR_* constant
 347          * @since 1.23
 348          */
 349         protected function setLastError( $err ) {
 350                 $this->lastError = $err;
 351         }
 352
 353         /**
 354          * @param string $text
 355          */
 356         public function debug( $text ) {
 357                 if ( $this->debugMode ) {
 358                         $class = get_class( $this );
 359                         wfDebug( "$class debug: $text\n" );
 360                 }
 361         }
 362
 363         /**
 364          * Convert an optionally relative time to an absolute time
 365          * @param int $exptime
 366          * @return int
 367          */
 368         protected function convertExpiry( $exptime ) {
 369                 if ( ( $exptime != 0 ) && ( $exptime < 86400 * 3650 /* 10 years */ ) ) {
 370                         return time() + $exptime;
 371                 } else {
 372                         return $exptime;
 373                 }
 374         }
 375
 376         /**
 377          * Convert an optionally absolute expiry time to a relative time. If an
 378          * absolute time is specified which is in the past, use a short expiry time.
 379          *
 380          * @param int $exptime
 381          * @return int
 382          */
 383         protected function convertToRelative( $exptime ) {
 384                 if ( $exptime >= 86400 * 3650 /* 10 years */ ) {
 385                         $exptime -= time();
 386                         if ( $exptime <= 0 ) {
 387                                 $exptime = 1;
 388                         }
 389                         return $exptime;
 390                 } else {
 391                         return $exptime;
 392                 }
 393         }
 394
 395         /**
 396          * Check if a value is an integer
 397          *
 398          * @param mixed $value
 399          * @return bool
 400          */
 401         protected function isInteger( $value ) {
 402                 return ( is_int( $value ) || ctype_digit( $value ) );
 403         }
 404 }