includes/libs/objectcache/APCUBagOStuff.php

   1 <?php
   2 /**
   3  * This program is free software; you can redistribute it and/or modify
   4  * it under the terms of the GNU General Public License as published by
   5  * the Free Software Foundation; either version 2 of the License, or
   6  * (at your option) any later version.
   7  *
   8  * This program is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  11  * GNU General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  16  * http://www.gnu.org/copyleft/gpl.html
  17  *
  18  * @file
  19  */
  20 namespace Wikimedia\ObjectCache;
  21
  22 /**
  23  * Store data in the local server memory via APCu (php-apcu)
  24  *
  25  * Past issues of note:
  26  * - Memory corruption when `apc.serializer=default` in INI:
  27  *   https://phabricator.wikimedia.org/T120267
  28  * - We used to recommend `apc.serializer=php` as non-default setting, and if not set,
  29  *   applied serialize() manually to workaround bugs and to create values we can use
  30  *   as CAS tokens. Upstream defaults to serializer=php since php-apcu 5.1.15 (2018).
  31  *   https://gerrit.wikimedia.org/r/671634
  32  *
  33  * @see https://www.php.net/apcu
  34  * @ingroup Cache
  35  */
  36 class APCUBagOStuff extends MediumSpecificBagOStuff {
  37         /**
  38          * @var string String to append to each APC key. This may be changed
  39          *  whenever the handling of values is changed, to prevent existing code
  40          *  from encountering older values which it cannot handle.
  41          */
  42         private const KEY_SUFFIX = ':5';
  43
  44         /** @var int Max attempts for implicit CAS operations */
  45         private static $CAS_MAX_ATTEMPTS = 100;
  46
  47         public function __construct( array $params = [] ) {
  48                 // No use in segmenting values
  49                 $params['segmentationSize'] = INF;
  50                 parent::__construct( $params );
  51                 // Versions of apcu < 5.1.19 use apc.use_request_time=1 by default, causing new keys
  52                 // to be assigned timestamps based on the start of the PHP request/script. The longer
  53                 // the request has been running, the more likely that newly stored keys will instantly
  54                 // be seen as expired by other requests. Disable apc.use_request_time.
  55                 ini_set( 'apc.use_request_time', '0' );
  56
  57                 if ( PHP_SAPI === 'cli' ) {
  58                         $this->attrMap[self::ATTR_DURABILITY] = ini_get( 'apc.enable_cli' )
  59                                 ? self::QOS_DURABILITY_SCRIPT
  60                                 : self::QOS_DURABILITY_NONE;
  61                 } else {
  62                         $this->attrMap[self::ATTR_DURABILITY] = self::QOS_DURABILITY_SERVICE;
  63                 }
  64         }
  65
  66         protected function doGet( $key, $flags = 0, &$casToken = null ) {
  67                 $getToken = ( $casToken === self::PASS_BY_REF );
  68                 $casToken = null;
  69
  70                 $value = apcu_fetch( $key . self::KEY_SUFFIX );
  71                 if ( $getToken && $value !== false ) {
  72                         // Note that if the driver handles serialization then this uses the PHP value
  73                         // as the token. This might require inspection or re-serialization in doCas().
  74                         $casToken = $value;
  75                 }
  76
  77                 return $value;
  78         }
  79
  80         protected function doSet( $key, $value, $exptime = 0, $flags = 0 ) {
  81                 $ttl = $this->getExpirationAsTTL( $exptime );
  82
  83                 return apcu_store( $key . self::KEY_SUFFIX, $value, $ttl );
  84         }
  85
  86         protected function doAdd( $key, $value, $exptime = 0, $flags = 0 ) {
  87                 if ( apcu_exists( $key . self::KEY_SUFFIX ) ) {
  88                         // Avoid global write locks for high contention keys
  89                         return false;
  90                 }
  91
  92                 $ttl = $this->getExpirationAsTTL( $exptime );
  93
  94                 return apcu_add( $key . self::KEY_SUFFIX, $value, $ttl );
  95         }
  96
  97         protected function doDelete( $key, $flags = 0 ) {
  98                 apcu_delete( $key . self::KEY_SUFFIX );
  99
 100                 return true;
 101         }
 102
 103         protected function doIncrWithInit( $key, $exptime, $step, $init, $flags ) {
 104                 // Use apcu 5.1.12 $ttl argument if apcu_inc() will initialize to $init:
 105                 // https://www.php.net/manual/en/function.apcu-inc.php
 106                 if ( $step === $init ) {
 107                         /** @noinspection PhpMethodParametersCountMismatchInspection */
 108                         $ttl = $this->getExpirationAsTTL( $exptime );
 109                         $result = apcu_inc( $key . self::KEY_SUFFIX, $step, $success, $ttl );
 110                 } else {
 111                         $result = false;
 112                         for ( $i = 0; $i < self::$CAS_MAX_ATTEMPTS; ++$i ) {
 113                                 $oldCount = apcu_fetch( $key . self::KEY_SUFFIX );
 114                                 if ( $oldCount === false ) {
 115                                         $count = $init;
 116                                         $ttl = $this->getExpirationAsTTL( $exptime );
 117                                         if ( apcu_add( $key . self::KEY_SUFFIX, $count, $ttl ) ) {
 118                                                 $result = $count;
 119                                                 break;
 120                                         }
 121                                 } elseif ( is_int( $oldCount ) ) {
 122                                         $count = $oldCount + $step;
 123                                         if ( apcu_cas( $key . self::KEY_SUFFIX, $oldCount, $count ) ) {
 124                                                 $result = $count;
 125                                                 break;
 126                                         }
 127                                 } else {
 128                                         break;
 129                                 }
 130                         }
 131                 }
 132
 133                 return $result;
 134         }
 135 }
 136
 137 /** @deprecated class alias since 1.43 */
 138 class_alias( APCUBagOStuff::class, 'APCUBagOStuff' );