includes/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
  24 /**
  25  * A cache class that replicates all writes to multiple child caches. Reads
  26  * are implemented by reading from the caches in the order they are given in
  27  * the configuration until a cache gives a positive result.
  28  *
  29  * @ingroup Cache
  30  */
  31 class MultiWriteBagOStuff extends BagOStuff {
  32         /** @var BagOStuff[] */
  33         protected $caches;
  34         /** @var bool Use async secondary writes */
  35         protected $asyncWrites = false;
  36         /** @var callback|null */
  37         protected $asyncHandler;
  38
  39         /** Idiom for "write to all backends" */
  40         const ALL = INF;
  41
  42         const UPGRADE_TTL = 3600; // TTL when a key is copied to a higher cache tier
  43
  44         /**
  45          * $params include:
  46          *   - caches: A numbered array of either ObjectFactory::getObjectFromSpec
  47          *      arrays yeilding BagOStuff objects or direct BagOStuff objects.
  48          *      If using the former, the 'args' field *must* be set.
  49          *      The first cache is the primary one, being the first to
  50          *      be read in the fallback chain. Writes happen to all stores
  51          *      in the order they are defined. However, lock()/unlock() calls
  52          *      only use the primary store.
  53          *   - replication: Either 'sync' or 'async'. This controls whether writes
  54          *      to secondary stores are deferred when possible. Async writes
  55          *      require setting 'asyncCallback'. HHVM register_postsend_function() function.
  56          *      Async writes can increase the chance of some race conditions
  57          *      or cause keys to expire seconds later than expected. It is
  58          *      safe to use for modules when cached values: are immutable,
  59          *      invalidation uses logical TTLs, invalidation uses etag/timestamp
  60          *      validation against the DB, or merge() is used to handle races.
  61          *   - asyncHandler: callable that takes a callback and runs it after the
  62          *      current web request ends. In CLI mode, it should run it immediately.
  63          * @param array $params
  64          * @throws InvalidArgumentException
  65          */
  66         public function __construct( $params ) {
  67                 parent::__construct( $params );
  68
  69                 if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
  70                         throw new InvalidArgumentException(
  71                                 __METHOD__ . ': "caches" parameter must be an array of caches'
  72                         );
  73                 }
  74
  75                 $this->caches = array();
  76                 foreach ( $params['caches'] as $cacheInfo ) {
  77                         if ( $cacheInfo instanceof BagOStuff ) {
  78                                 $this->caches[] = $cacheInfo;
  79                         } else {
  80                                 if ( !isset( $cacheInfo['args'] ) ) {
  81                                         // B/C for when $cacheInfo was for ObjectCache::newFromParams().
  82                                         // Callers intenting this to be for ObjectFactory::getObjectFromSpec
  83                                         // should have set "args" per the docs above. Doings so avoids extra
  84                                         // (likely harmless) params (factory/class/calls) ending up in "args".
  85                                         $cacheInfo['args'] = array( $cacheInfo );
  86                                 }
  87                                 $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
  88                         }
  89                 }
  90
  91                 $this->asyncHandler = isset( $params['asyncHandler'] )
  92                         ? $params['asyncHandler']
  93                         : null;
  94                 $this->asyncWrites = (
  95                         isset( $params['replication'] ) &&
  96                         $params['replication'] === 'async' &&
  97                         is_callable( $this->asyncHandler )
  98                 );
  99         }
 100
 101         public function setDebug( $debug ) {
 102                 foreach ( $this->caches as $cache ) {
 103                         $cache->setDebug( $debug );
 104                 }
 105         }
 106
 107         protected function doGet( $key, $flags = 0 ) {
 108                 if ( ( $flags & self::READ_LATEST ) == self::READ_LATEST ) {
 109                         // If the latest write was a delete(), we do NOT want to fallback
 110                         // to the other tiers and possibly see the old value. Also, this
 111                         // is used by mergeViaLock(), which only needs to hit the primary.
 112                         return $this->caches[0]->get( $key, $flags );
 113                 }
 114
 115                 $misses = 0; // number backends checked
 116                 $value = false;
 117                 foreach ( $this->caches as $cache ) {
 118                         $value = $cache->get( $key, $flags );
 119                         if ( $value !== false ) {
 120                                 break;
 121                         }
 122                         ++$misses;
 123                 }
 124
 125                 if ( $value !== false
 126                         && $misses > 0
 127                         && ( $flags & self::READ_VERIFIED ) == self::READ_VERIFIED
 128                 ) {
 129                         $this->doWrite( $misses, $this->asyncWrites, 'set', $key, $value, self::UPGRADE_TTL );
 130                 }
 131
 132                 return $value;
 133         }
 134
 135         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 136                 $asyncWrites = ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC )
 137                         ? false
 138                         : $this->asyncWrites;
 139
 140                 return $this->doWrite( self::ALL, $asyncWrites, 'set', $key, $value, $exptime );
 141         }
 142
 143         public function delete( $key ) {
 144                 return $this->doWrite( self::ALL, $this->asyncWrites, 'delete', $key );
 145         }
 146
 147         public function add( $key, $value, $exptime = 0 ) {
 148                 return $this->doWrite( self::ALL, $this->asyncWrites, 'add', $key, $value, $exptime );
 149         }
 150
 151         public function incr( $key, $value = 1 ) {
 152                 return $this->doWrite( self::ALL, $this->asyncWrites, 'incr', $key, $value );
 153         }
 154
 155         public function decr( $key, $value = 1 ) {
 156                 return $this->doWrite( self::ALL, $this->asyncWrites, 'decr', $key, $value );
 157         }
 158
 159         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 160                 // Only need to lock the first cache; also avoids deadlocks
 161                 return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
 162         }
 163
 164         public function unlock( $key ) {
 165                 // Only the first cache is locked
 166                 return $this->caches[0]->unlock( $key );
 167         }
 168
 169         public function getLastError() {
 170                 return $this->caches[0]->getLastError();
 171         }
 172
 173         public function clearLastError() {
 174                 $this->caches[0]->clearLastError();
 175         }
 176
 177         /**
 178          * Apply a write method to the first $count backing caches
 179          *
 180          * @param integer $count
 181          * @param bool $asyncWrites
 182          * @param string $method
 183          * @param mixed ...
 184          * @return bool
 185          */
 186         protected function doWrite( $count, $asyncWrites, $method /*, ... */ ) {
 187                 $ret = true;
 188                 $args = array_slice( func_get_args(), 3 );
 189
 190                 foreach ( $this->caches as $i => $cache ) {
 191                         if ( $i >= $count ) {
 192                                 break; // ignore the lower tiers
 193                         }
 194
 195                         if ( $i == 0 || !$asyncWrites ) {
 196                                 // First store or in sync mode: write now and get result
 197                                 if ( !call_user_func_array( array( $cache, $method ), $args ) ) {
 198                                         $ret = false;
 199                                 }
 200                         } else {
 201                                 // Secondary write in async mode: do not block this HTTP request
 202                                 $logger = $this->logger;
 203                                 call_user_func(
 204                                         $this->asyncHandler,
 205                                         function () use ( $cache, $method, $args, $logger ) {
 206                                                 if ( !call_user_func_array( array( $cache, $method ), $args ) ) {
 207                                                         $logger->warning( "Async $method op failed" );
 208                                                 }
 209                                         }
 210                                 );
 211                         }
 212                 }
 213
 214                 return $ret;
 215         }
 216
 217         /**
 218          * Delete objects expiring before a certain date.
 219          *
 220          * Succeed if any of the child caches succeed.
 221          * @param string $date
 222          * @param bool|callable $progressCallback
 223          * @return bool
 224          */
 225         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 226                 $ret = false;
 227                 foreach ( $this->caches as $cache ) {
 228                         if ( $cache->deleteObjectsExpiringBefore( $date, $progressCallback ) ) {
 229                                 $ret = true;
 230                         }
 231                 }
 232
 233                 return $ret;
 234         }
 235 }