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         /** @var int[] List of all backing cache indexes */
  38         protected $cacheIndexes = [];
  39
  40         const UPGRADE_TTL = 3600; // TTL when a key is copied to a higher cache tier
  41
  42         /**
  43          * $params include:
  44          *   - caches: A numbered array of either ObjectFactory::getObjectFromSpec
  45          *      arrays yeilding BagOStuff objects or direct BagOStuff objects.
  46          *      If using the former, the 'args' field *must* be set.
  47          *      The first cache is the primary one, being the first to
  48          *      be read in the fallback chain. Writes happen to all stores
  49          *      in the order they are defined. However, lock()/unlock() calls
  50          *      only use the primary store.
  51          *   - replication: Either 'sync' or 'async'. This controls whether writes
  52          *      to secondary stores are deferred when possible. Async writes
  53          *      require setting 'asyncHandler'. HHVM register_postsend_function() function.
  54          *      Async writes can increase the chance of some race conditions
  55          *      or cause keys to expire seconds later than expected. It is
  56          *      safe to use for modules when cached values: are immutable,
  57          *      invalidation uses logical TTLs, invalidation uses etag/timestamp
  58          *      validation against the DB, or merge() is used to handle races.
  59          * @param array $params
  60          * @throws InvalidArgumentException
  61          */
  62         public function __construct( $params ) {
  63                 parent::__construct( $params );
  64
  65                 if ( empty( $params['caches'] ) || !is_array( $params['caches'] ) ) {
  66                         throw new InvalidArgumentException(
  67                                 __METHOD__ . ': "caches" parameter must be an array of caches'
  68                         );
  69                 }
  70
  71                 $this->caches = [];
  72                 foreach ( $params['caches'] as $cacheInfo ) {
  73                         if ( $cacheInfo instanceof BagOStuff ) {
  74                                 $this->caches[] = $cacheInfo;
  75                         } else {
  76                                 if ( !isset( $cacheInfo['args'] ) ) {
  77                                         // B/C for when $cacheInfo was for ObjectCache::newFromParams().
  78                                         // Callers intenting this to be for ObjectFactory::getObjectFromSpec
  79                                         // should have set "args" per the docs above. Doings so avoids extra
  80                                         // (likely harmless) params (factory/class/calls) ending up in "args".
  81                                         $cacheInfo['args'] = [ $cacheInfo ];
  82                                 }
  83                                 $this->caches[] = ObjectFactory::getObjectFromSpec( $cacheInfo );
  84                         }
  85                 }
  86                 $this->mergeFlagMaps( $this->caches );
  87
  88                 $this->asyncWrites = (
  89                         isset( $params['replication'] ) &&
  90                         $params['replication'] === 'async' &&
  91                         is_callable( $this->asyncHandler )
  92                 );
  93
  94                 $this->cacheIndexes = array_keys( $this->caches );
  95         }
  96
  97         public function setDebug( $debug ) {
  98                 foreach ( $this->caches as $cache ) {
  99                         $cache->setDebug( $debug );
 100                 }
 101         }
 102
 103         protected function doGet( $key, $flags = 0 ) {
 104                 if ( ( $flags & self::READ_LATEST ) == self::READ_LATEST ) {
 105                         // If the latest write was a delete(), we do NOT want to fallback
 106                         // to the other tiers and possibly see the old value. Also, this
 107                         // is used by mergeViaLock(), which only needs to hit the primary.
 108                         return $this->caches[0]->get( $key, $flags );
 109                 }
 110
 111                 $value = false;
 112                 $missIndexes = []; // backends checked
 113                 foreach ( $this->caches as $i => $cache ) {
 114                         $value = $cache->get( $key, $flags );
 115                         if ( $value !== false ) {
 116                                 break;
 117                         }
 118                         $missIndexes[] = $i;
 119                 }
 120
 121                 if ( $value !== false
 122                         && $missIndexes
 123                         && ( $flags & self::READ_VERIFIED ) == self::READ_VERIFIED
 124                 ) {
 125                         // Backfill the value to the higher (and often faster/smaller) cache tiers
 126                         $this->doWrite(
 127                                 $missIndexes, $this->asyncWrites, 'set', $key, $value, self::UPGRADE_TTL
 128                         );
 129                 }
 130
 131                 return $value;
 132         }
 133
 134         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 135                 $asyncWrites = ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC )
 136                         ? false
 137                         : $this->asyncWrites;
 138
 139                 return $this->doWrite( $this->cacheIndexes, $asyncWrites, 'set', $key, $value, $exptime );
 140         }
 141
 142         public function delete( $key, $flags = 0 ) {
 143                 return $this->doWrite( $this->cacheIndexes, $this->asyncWrites, 'delete', $key );
 144         }
 145
 146         public function add( $key, $value, $exptime = 0 ) {
 147                 // Try the write to the top-tier cache
 148                 $ok = $this->doWrite( [ 0 ], $this->asyncWrites, 'add', $key, $value, $exptime );
 149                 if ( $ok ) {
 150                         // Relay the add() using set() if it succeeded. This is meant to handle certain
 151                         // migration scenarios where the same store might get written to twice for certain
 152                         // keys. In that case, it does not make sense to return false due to "self-conflicts".
 153                         return $this->doWrite(
 154                                 array_slice( $this->cacheIndexes, 1 ),
 155                                 $this->asyncWrites,
 156                                 'set',
 157                                 $key,
 158                                 $value,
 159                                 $exptime
 160                         );
 161                 }
 162
 163                 return false;
 164         }
 165
 166         public function incr( $key, $value = 1 ) {
 167                 return $this->doWrite( $this->cacheIndexes, $this->asyncWrites, 'incr', $key, $value );
 168         }
 169
 170         public function decr( $key, $value = 1 ) {
 171                 return $this->doWrite( $this->cacheIndexes, $this->asyncWrites, 'decr', $key, $value );
 172         }
 173
 174         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 175                 $asyncWrites = ( ( $flags & self::WRITE_SYNC ) == self::WRITE_SYNC )
 176                         ? false
 177                         : $this->asyncWrites;
 178
 179                 return $this->doWrite(
 180                         $this->cacheIndexes,
 181                         $asyncWrites,
 182                         'merge',
 183                         $key,
 184                         $callback,
 185                         $exptime,
 186                         $attempts,
 187                         $flags
 188                 );
 189         }
 190
 191         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 192                 // Only need to lock the first cache; also avoids deadlocks
 193                 return $this->caches[0]->lock( $key, $timeout, $expiry, $rclass );
 194         }
 195
 196         public function unlock( $key ) {
 197                 // Only the first cache is locked
 198                 return $this->caches[0]->unlock( $key );
 199         }
 200
 201         public function getLastError() {
 202                 return $this->caches[0]->getLastError();
 203         }
 204
 205         public function clearLastError() {
 206                 $this->caches[0]->clearLastError();
 207         }
 208
 209         /**
 210          * Apply a write method to the backing caches specified by $indexes (in order)
 211          *
 212          * @param int[] $indexes List of backing cache indexes
 213          * @param bool $asyncWrites
 214          * @param string $method
 215          * @param mixed $args,...
 216          * @return bool
 217          */
 218         protected function doWrite( $indexes, $asyncWrites, $method /*, ... */ ) {
 219                 $ret = true;
 220                 $args = array_slice( func_get_args(), 3 );
 221
 222                 if ( array_diff( $indexes, [ 0 ] ) && $asyncWrites && $method !== 'merge' ) {
 223                         // Deep-clone $args to prevent misbehavior when something writes an
 224                         // object to the BagOStuff then modifies it afterwards, e.g. T168040.
 225                         $args = unserialize( serialize( $args ) );
 226                 }
 227
 228                 foreach ( $indexes as $i ) {
 229                         $cache = $this->caches[$i];
 230                         if ( $i == 0 || !$asyncWrites ) {
 231                                 // First store or in sync mode: write now and get result
 232                                 if ( !$cache->$method( ...$args ) ) {
 233                                         $ret = false;
 234                                 }
 235                         } else {
 236                                 // Secondary write in async mode: do not block this HTTP request
 237                                 $logger = $this->logger;
 238                                 ( $this->asyncHandler )(
 239                                         function () use ( $cache, $method, $args, $logger ) {
 240                                                 if ( !$cache->$method( ...$args ) ) {
 241                                                         $logger->warning( "Async $method op failed" );
 242                                                 }
 243                                         }
 244                                 );
 245                         }
 246                 }
 247
 248                 return $ret;
 249         }
 250
 251         /**
 252          * Delete objects expiring before a certain date.
 253          *
 254          * Succeed if any of the child caches succeed.
 255          * @param string $date
 256          * @param bool|callable $progressCallback
 257          * @return bool
 258          */
 259         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 260                 $ret = false;
 261                 foreach ( $this->caches as $cache ) {
 262                         if ( $cache->deleteObjectsExpiringBefore( $date, $progressCallback ) ) {
 263                                 $ret = true;
 264                         }
 265                 }
 266
 267                 return $ret;
 268         }
 269
 270         public function makeKeyInternal( $keyspace, $args ) {
 271                 return $this->caches[0]->makeKeyInternal( ...func_get_args() );
 272         }
 273
 274         public function makeKey( $class, $component = null ) {
 275                 return $this->caches[0]->makeKey( ...func_get_args() );
 276         }
 277
 278         public function makeGlobalKey( $class, $component = null ) {
 279                 return $this->caches[0]->makeGlobalKey( ...func_get_args() );
 280         }
 281 }