includes/libs/objectcache/MultiWriteBagOStuff.php

   1 <?php
   2 /**
   3  * Wrapper for object caching in different caches.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Cache
  22  */
  23 use Wikimedia\ObjectFactory;
  24
  25 /**
  26  * A cache class that replicates all writes to multiple child caches. Reads
  27  * are implemented by reading from the caches in the order they are given in
  28  * the configuration until a cache gives a positive result.
  29  *
  30  * @ingroup Cache
  31  */
  32 class MultiWriteBagOStuff extends BagOStuff {
  33         /** @var BagOStuff[] */
  34         protected $caches;
  35         /** @var bool Use async secondary writes */
  36         protected $asyncWrites = false;
  37
  38         /** Idiom for "write to all backends" */
  39         const ALL = INF;
  40
  41         const UPGRADE_TTL = 3600; // TTL when a key is copied to a higher cache tier
  42
  43         /**
  44          * $params include:
  45          *   - caches: A numbered array of either ObjectFactory::getObjectFromSpec
  46          *      arrays yeilding BagOStuff objects or direct BagOStuff objects.
  47          *      If using the former, the 'args' field *must* be set.
  48          *      The first cache is the primary one, being the first to
  49          *      be read in the fallback chain. Writes happen to all stores
  50          *      in the order they are defined. However, lock()/unlock() calls
  51          *      only use the primary store.
  52          *   - replication: Either 'sync' or 'async'. This controls whether writes
  53          *      to secondary stores are deferred when possible. Async writes
  54          *      require setting 'asyncHandler'. HHVM register_postsend_function() function.
  55          *      Async writes can increase the chance of some race conditions
  56          *      or cause keys to expire seconds later than expected. It is
  57          *      safe to use for modules when cached values: are immutable,
  58          *      invalidation uses logical TTLs, invalidation uses etag/timestamp
  59          *      validation against the DB, or merge() is used to handle races.
  60          * @param array $params
  61          * @throws InvalidArgumentException
  62          */
  63         public function __construct( $params ) {
  64                 parent::__construct( $params );
  65
  66                 if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
  67                         throw new InvalidArgumentException(
  68                                 __METHOD__ . ': "caches" parameter must be an array of caches'
  69                         );
  70                 }
  71
  72                 $this->caches = [];
  73                 foreach ( $params['caches'] as $cacheInfo ) {
  74                         if ( $cacheInfo instanceof BagOStuff ) {
  75                                 $this->caches[] = $cacheInfo;
  76                         } else {
  77                                 if ( !isset( $cacheInfo['args'] ) ) {
  78                                         // B/C for when $cacheInfo was for ObjectCache::newFromParams().
  79                                         // Callers intenting this to be for ObjectFactory::getObjectFromSpec
  80                                         // should have set "args" per the docs above. Doings so avoids extra
  81                                         // (likely harmless) params (factory/class/calls) ending up in "args".
  82                                         $cacheInfo['args'] = [ $cacheInfo ];
  83                                 }
  84                                 $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
  85                         }
  86                 }
  87                 $this->mergeFlagMaps( $this->caches );
  88
  89                 $this->asyncWrites = (
  90                         isset( $params['replication'] ) &&
  91                         $params['replication'] === 'async' &&
  92                         is_callable( $this->asyncHandler )
  93                 );
  94         }
  95
  96         public function setDebug( $debug ) {
  97                 foreach ( $this->caches as $cache ) {
  98                         $cache->setDebug( $debug );
  99                 }
 100         }
 101
 102         protected function doGet( $key, $flags = 0 ) {
 103                 if ( ( $flags & self::READ_LATEST ) == self::READ_LATEST ) {
 104                         // If the latest write was a delete(), we do NOT want to fallback
 105                         // to the other tiers and possibly see the old value. Also, this
 106                         // is used by mergeViaLock(), which only needs to hit the primary.
 107                         return $this->caches[0]->get( $key, $flags );
 108                 }
 109
 110                 $misses = 0; // number backends checked
 111                 $value = false;
 112                 foreach ( $this->caches as $cache ) {
 113                         $value = $cache->get( $key, $flags );
 114                         if ( $value !== false ) {
 115                                 break;
 116                         }
 117                         ++$misses;
 118                 }
 119
 120                 if ( $value !== false
 121                         && $misses > 0
 122                         && ( $flags & self::READ_VERIFIED ) == self::READ_VERIFIED
 123                 ) {
 124                         $this->doWrite( $misses, $this->asyncWrites, 'set', $key, $value, self::UPGRADE_TTL );
 125                 }
 126
 127                 return $value;
 128         }
 129
 130         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 131                 $asyncWrites = ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC )
 132                         ? false
 133                         : $this->asyncWrites;
 134
 135                 return $this->doWrite( self::ALL, $asyncWrites, 'set', $key, $value, $exptime );
 136         }
 137
 138         public function delete( $key ) {
 139                 return $this->doWrite( self::ALL, $this->asyncWrites, 'delete', $key );
 140         }
 141
 142         public function add( $key, $value, $exptime = 0 ) {
 143                 return $this->doWrite( self::ALL, $this->asyncWrites, 'add', $key, $value, $exptime );
 144         }
 145
 146         public function incr( $key, $value = 1 ) {
 147                 return $this->doWrite( self::ALL, $this->asyncWrites, 'incr', $key, $value );
 148         }
 149
 150         public function decr( $key, $value = 1 ) {
 151                 return $this->doWrite( self::ALL, $this->asyncWrites, 'decr', $key, $value );
 152         }
 153
 154         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 155                 // Only need to lock the first cache; also avoids deadlocks
 156                 return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
 157         }
 158
 159         public function unlock( $key ) {
 160                 // Only the first cache is locked
 161                 return $this->caches[0]->unlock( $key );
 162         }
 163
 164         public function getLastError() {
 165                 return $this->caches[0]->getLastError();
 166         }
 167
 168         public function clearLastError() {
 169                 $this->caches[0]->clearLastError();
 170         }
 171
 172         /**
 173          * Apply a write method to the first $count backing caches
 174          *
 175          * @param int $count
 176          * @param bool $asyncWrites
 177          * @param string $method
 178          * @param mixed $args,...
 179          * @return bool
 180          */
 181         protected function doWrite( $count, $asyncWrites, $method /*, ... */ ) {
 182                 $ret = true;
 183                 $args = array_slice( func_get_args(), 3 );
 184
 185                 if ( $count > 1 && $asyncWrites ) {
 186                         // Deep-clone $args to prevent misbehavior when something writes an
 187                         // object to the BagOStuff then modifies it afterwards, e.g. T168040.
 188                         $args = unserialize( serialize( $args ) );
 189                 }
 190
 191                 foreach ( $this->caches as $i => $cache ) {
 192                         if ( $i >= $count ) {
 193                                 break; // ignore the lower tiers
 194                         }
 195
 196                         if ( $i == 0 || !$asyncWrites ) {
 197                                 // First store or in sync mode: write now and get result
 198                                 if ( !call_user_func_array( [ $cache, $method ], $args ) ) {
 199                                         $ret = false;
 200                                 }
 201                         } else {
 202                                 // Secondary write in async mode: do not block this HTTP request
 203                                 $logger = $this->logger;
 204                                 call_user_func(
 205                                         $this->asyncHandler,
 206                                         function () use ( $cache, $method, $args, $logger ) {
 207                                                 if ( !call_user_func_array( [ $cache, $method ], $args ) ) {
 208                                                         $logger->warning( "Async $method op failed" );
 209                                                 }
 210                                         }
 211                                 );
 212                         }
 213                 }
 214
 215                 return $ret;
 216         }
 217
 218         /**
 219          * Delete objects expiring before a certain date.
 220          *
 221          * Succeed if any of the child caches succeed.
 222          * @param string $date
 223          * @param bool|callable $progressCallback
 224          * @return bool
 225          */
 226         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 227                 $ret = false;
 228                 foreach ( $this->caches as $cache ) {
 229                         if ( $cache->deleteObjectsExpiringBefore( $date, $progressCallback ) ) {
 230                                 $ret = true;
 231                         }
 232                 }
 233
 234                 return $ret;
 235         }
 236
 237         public function makeKey( $class, $component = null ) {
 238                 return call_user_func_array( [ $this->caches[0], __FUNCTION__ ], func_get_args() );
 239         }
 240
 241         public function makeGlobalKey( $class, $component = null ) {
 242                 return call_user_func_array( [ $this->caches[0], __FUNCTION__ ], func_get_args() );
 243         }
 244 }