includes/libs/objectcache/BagOStuff.php

   1 <?php
   2 /**
   3  * Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
   4  * https://www.mediawiki.org/
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License along
  17  * with this program; if not, write to the Free Software Foundation, Inc.,
  18  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  19  * http://www.gnu.org/copyleft/gpl.html
  20  *
  21  * @file
  22  * @ingroup Cache
  23  */
  24
  25 /**
  26  * @defgroup Cache Cache
  27  */
  28
  29 use Psr\Log\LoggerAwareInterface;
  30 use Psr\Log\LoggerInterface;
  31 use Psr\Log\NullLogger;
  32 use Wikimedia\ScopedCallback;
  33 use Wikimedia\WaitConditionLoop;
  34
  35 /**
  36  * Class representing a cache/ephemeral data store
  37  *
  38  * This interface is intended to be more or less compatible with the PHP memcached client.
  39  *
  40  * Instances of this class should be created with an intended access scope, such as:
  41  *   - a) A single PHP thread on a server (e.g. stored in a PHP variable)
  42  *   - b) A single application server (e.g. stored in APC or sqlite)
  43  *   - c) All application servers in datacenter (e.g. stored in memcached or mysql)
  44  *   - d) All application servers in all datacenters (e.g. stored via mcrouter or dynomite)
  45  *
  46  * Callers should use the proper factory methods that yield BagOStuff instances. Site admins
  47  * should make sure the configuration for those factory methods matches their access scope.
  48  * BagOStuff subclasses have widely varying levels of support for replication features.
  49  *
  50  * For any given instance, methods like lock(), unlock(), merge(), and set() with WRITE_SYNC
  51  * should semantically operate over its entire access scope; any nodes/threads in that scope
  52  * should serialize appropriately when using them. Likewise, a call to get() with READ_LATEST
  53  * from one node in its access scope should reflect the prior changes of any other node its
  54  * access scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
  55  *
  56  * Subclasses should override the default "segmentationSize" field with an appropriate value.
  57  * The value should not be larger than what the storage backend (by default) supports. It also
  58  * should be roughly informed by common performance bottlenecks (e.g. values over a certain size
  59  * having poor scalability). The same goes for the "segmentedValueMaxSize" member, which limits
  60  * the maximum size and chunk count (indirectly) of values.
  61  *
  62  * @ingroup Cache
  63  */
  64 abstract class BagOStuff implements IExpiringStore, IStoreKeyEncoder, LoggerAwareInterface {
  65         /** @var array[] Lock tracking */
  66         protected $locks = [];
  67         /** @var int ERR_* class constant */
  68         protected $lastError = self::ERR_NONE;
  69         /** @var string */
  70         protected $keyspace = 'local';
  71         /** @var LoggerInterface */
  72         protected $logger;
  73         /** @var callable|null */
  74         protected $asyncHandler;
  75         /** @var int Seconds */
  76         protected $syncTimeout;
  77         /** @var int Bytes; chunk size of segmented cache values */
  78         protected $segmentationSize;
  79         /** @var int Bytes; maximum total size of a segmented cache value */
  80         protected $segmentedValueMaxSize;
  81
  82         /** @var bool */
  83         private $debugMode = false;
  84         /** @var array */
  85         private $duplicateKeyLookups = [];
  86         /** @var bool */
  87         private $reportDupes = false;
  88         /** @var bool */
  89         private $dupeTrackScheduled = false;
  90
  91         /** @var callable[] */
  92         protected $busyCallbacks = [];
  93
  94         /** @var float|null */
  95         private $wallClockOverride;
  96
  97         /** @var int[] Map of (ATTR_* class constant => QOS_* class constant) */
  98         protected $attrMap = [];
  99
 100         /** Bitfield constants for get()/getMulti(); these are only advisory */
 101         const READ_LATEST = 1; // if supported, avoid reading stale data due to replication
 102         const READ_VERIFIED = 2; // promise that the caller handles detection of staleness
 103         /** Bitfield constants for set()/merge(); these are only advisory */
 104         const WRITE_SYNC = 4; // if supported, block until the write is fully replicated
 105         const WRITE_CACHE_ONLY = 8; // only change state of the in-memory cache
 106         const WRITE_ALLOW_SEGMENTS = 16; // allow partitioning of the value if it is large
 107         const WRITE_PRUNE_SEGMENTS = 32; // delete all the segments if the value is partitioned
 108         const WRITE_BACKGROUND = 64; // if supported,
 109
 110         /** @var string Component to use for key construction of blob segment keys */
 111         const SEGMENT_COMPONENT = 'segment';
 112
 113         /**
 114          * $params include:
 115          *   - logger: Psr\Log\LoggerInterface instance
 116          *   - keyspace: Default keyspace for $this->makeKey()
 117          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
 118          *      In CLI mode, it should run the task immediately.
 119          *   - reportDupes: Whether to emit warning log messages for all keys that were
 120          *      requested more than once (requires an asyncHandler).
 121          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
 122          *   - segmentationSize: The chunk size, in bytes, of segmented values. The value should
 123          *      not exceed the maximum size of values in the storage backend, as configured by
 124          *      the site administrator.
 125          *   - segmentedValueMaxSize: The maximum total size, in bytes, of segmented values.
 126          *      This should be configured to a reasonable size give the site traffic and the
 127          *      amount of I/O between application and cache servers that the network can handle.
 128          * @param array $params
 129          */
 130         public function __construct( array $params = [] ) {
 131                 $this->setLogger( $params['logger'] ?? new NullLogger() );
 132
 133                 if ( isset( $params['keyspace'] ) ) {
 134                         $this->keyspace = $params['keyspace'];
 135                 }
 136
 137                 $this->asyncHandler = $params['asyncHandler'] ?? null;
 138
 139                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 140                         $this->reportDupes = true;
 141                 }
 142
 143                 $this->syncTimeout = $params['syncTimeout'] ?? 3;
 144                 $this->segmentationSize = $params['segmentationSize'] ?? 8388608; // 8MiB
 145                 $this->segmentedValueMaxSize = $params['segmentedValueMaxSize'] ?? 67108864; // 64MiB
 146         }
 147
 148         /**
 149          * @param LoggerInterface $logger
 150          * @return void
 151          */
 152         public function setLogger( LoggerInterface $logger ) {
 153                 $this->logger = $logger;
 154         }
 155
 156         /**
 157          * @param bool $bool
 158          */
 159         public function setDebug( $bool ) {
 160                 $this->debugMode = $bool;
 161         }
 162
 163         /**
 164          * Get an item with the given key, regenerating and setting it if not found
 165          *
 166          * Nothing is stored nor deleted if the callback returns false
 167          *
 168          * @param string $key
 169          * @param int $ttl Time-to-live (seconds)
 170          * @param callable $callback Callback that derives the new value
 171          * @param int $flags Bitfield of BagOStuff::READ_* or BagOStuff::WRITE_* constants [optional]
 172          * @return mixed The cached value if found or the result of $callback otherwise
 173          * @since 1.27
 174          */
 175         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 176                 $value = $this->get( $key, $flags );
 177
 178                 if ( $value === false ) {
 179                         if ( !is_callable( $callback ) ) {
 180                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 181                         }
 182                         $value = call_user_func( $callback );
 183                         if ( $value !== false ) {
 184                                 $this->set( $key, $value, $ttl, $flags );
 185                         }
 186                 }
 187
 188                 return $value;
 189         }
 190
 191         /**
 192          * Get an item with the given key
 193          *
 194          * If the key includes a deterministic input hash (e.g. the key can only have
 195          * the correct value) or complete staleness checks are handled by the caller
 196          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 197          * This lets tiered backends know they can safely upgrade a cached value to
 198          * higher tiers using standard TTLs.
 199          *
 200          * @param string $key
 201          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 202          * @return mixed Returns false on failure or if the item does not exist
 203          */
 204         public function get( $key, $flags = 0 ) {
 205                 $this->trackDuplicateKeys( $key );
 206
 207                 return $this->resolveSegments( $key, $this->doGet( $key, $flags ) );
 208         }
 209
 210         /**
 211          * Track the number of times that a given key has been used.
 212          * @param string $key
 213          */
 214         private function trackDuplicateKeys( $key ) {
 215                 if ( !$this->reportDupes ) {
 216                         return;
 217                 }
 218
 219                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 220                         // Track that we have seen this key. This N-1 counting style allows
 221                         // easy filtering with array_filter() later.
 222                         $this->duplicateKeyLookups[$key] = 0;
 223                 } else {
 224                         $this->duplicateKeyLookups[$key] += 1;
 225
 226                         if ( $this->dupeTrackScheduled === false ) {
 227                                 $this->dupeTrackScheduled = true;
 228                                 // Schedule a callback that logs keys processed more than once by get().
 229                                 call_user_func( $this->asyncHandler, function () {
 230                                         $dups = array_filter( $this->duplicateKeyLookups );
 231                                         foreach ( $dups as $key => $count ) {
 232                                                 $this->logger->warning(
 233                                                         'Duplicate get(): "{key}" fetched {count} times',
 234                                                         // Count is N-1 of the actual lookup count
 235                                                         [ 'key' => $key, 'count' => $count + 1, ]
 236                                                 );
 237                                         }
 238                                 } );
 239                         }
 240                 }
 241         }
 242
 243         /**
 244          * @param string $key
 245          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 246          * @param mixed|null &$casToken Token to use for check-and-set comparisons
 247          * @return mixed Returns false on failure or if the item does not exist
 248          */
 249         abstract protected function doGet( $key, $flags = 0, &$casToken = null );
 250
 251         /**
 252          * Set an item
 253          *
 254          * @param string $key
 255          * @param mixed $value
 256          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 257          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 258          * @return bool Success
 259          */
 260         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 261                 if (
 262                         is_int( $value ) || // avoid breaking incr()/decr()
 263                         ( $flags & self::WRITE_ALLOW_SEGMENTS ) != self::WRITE_ALLOW_SEGMENTS ||
 264                         is_infinite( $this->segmentationSize )
 265                 ) {
 266                         return $this->doSet( $key, $value, $exptime, $flags );
 267                 }
 268
 269                 $serialized = $this->serialize( $value );
 270                 $segmentSize = $this->getSegmentationSize();
 271                 $maxTotalSize = $this->getSegmentedValueMaxSize();
 272
 273                 $size = strlen( $serialized );
 274                 if ( $size <= $segmentSize ) {
 275                         // Since the work of serializing it was already done, just use it inline
 276                         return $this->doSet(
 277                                 $key,
 278                                 SerializedValueContainer::newUnified( $serialized ),
 279                                 $exptime,
 280                                 $flags
 281                         );
 282                 } elseif ( $size > $maxTotalSize ) {
 283                         $this->setLastError( "Key $key exceeded $maxTotalSize bytes." );
 284
 285                         return false;
 286                 }
 287
 288                 $chunksByKey = [];
 289                 $segmentHashes = [];
 290                 $count = intdiv( $size, $segmentSize ) + ( ( $size % $segmentSize ) ? 1 : 0 );
 291                 for ( $i = 0; $i < $count; ++$i ) {
 292                         $segment = substr( $serialized, $i * $segmentSize, $segmentSize );
 293                         $hash = sha1( $segment );
 294                         $chunkKey = $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $hash );
 295                         $chunksByKey[$chunkKey] = $segment;
 296                         $segmentHashes[] = $hash;
 297                 }
 298
 299                 $flags &= ~self::WRITE_ALLOW_SEGMENTS; // sanity
 300                 $ok = $this->setMulti( $chunksByKey, $exptime, $flags );
 301                 if ( $ok ) {
 302                         // Only when all segments are stored should the main key be changed
 303                         $ok = $this->doSet(
 304                                 $key,
 305                                 SerializedValueContainer::newSegmented( $segmentHashes ),
 306                                 $exptime,
 307                                 $flags
 308                         );
 309                 }
 310
 311                 return $ok;
 312         }
 313
 314         /**
 315          * Set an item
 316          *
 317          * @param string $key
 318          * @param mixed $value
 319          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 320          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 321          * @return bool Success
 322          */
 323         abstract protected function doSet( $key, $value, $exptime = 0, $flags = 0 );
 324
 325         /**
 326          * Delete an item
 327          *
 328          * For large values written using WRITE_ALLOW_SEGMENTS, this only deletes the main
 329          * segment list key unless WRITE_PRUNE_SEGMENTS is in the flags. While deleting the segment
 330          * list key has the effect of functionally deleting the key, it leaves unused blobs in cache.
 331          *
 332          * @param string $key
 333          * @return bool True if the item was deleted or not found, false on failure
 334          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 335          */
 336         public function delete( $key, $flags = 0 ) {
 337                 if ( ( $flags & self::WRITE_PRUNE_SEGMENTS ) != self::WRITE_PRUNE_SEGMENTS ) {
 338                         return $this->doDelete( $key, $flags );
 339                 }
 340
 341                 $mainValue = $this->doGet( $key, self::READ_LATEST );
 342                 if ( !$this->doDelete( $key, $flags ) ) {
 343                         return false;
 344                 }
 345
 346                 if ( !SerializedValueContainer::isSegmented( $mainValue ) ) {
 347                         return true; // no segments to delete
 348                 }
 349
 350                 $orderedKeys = array_map(
 351                         function ( $segmentHash ) use ( $key ) {
 352                                 return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
 353                         },
 354                         $mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
 355                 );
 356
 357                 return $this->deleteMulti( $orderedKeys, $flags );
 358         }
 359
 360         /**
 361          * Delete an item
 362          *
 363          * @param string $key
 364          * @return bool True if the item was deleted or not found, false on failure
 365          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 366          */
 367         abstract protected function doDelete( $key, $flags = 0 );
 368
 369         /**
 370          * Insert an item if it does not already exist
 371          *
 372          * @param string $key
 373          * @param mixed $value
 374          * @param int $exptime
 375          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 376          * @return bool Success
 377          */
 378         abstract public function add( $key, $value, $exptime = 0, $flags = 0 );
 379
 380         /**
 381          * Merge changes into the existing cache value (possibly creating a new one)
 382          *
 383          * The callback function returns the new value given the current value
 384          * (which will be false if not present), and takes the arguments:
 385          * (this BagOStuff, cache key, current value, TTL).
 386          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 387          * Nothing is stored nor deleted if the callback returns false.
 388          *
 389          * @param string $key
 390          * @param callable $callback Callback method to be executed
 391          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 392          * @param int $attempts The amount of times to attempt a merge in case of failure
 393          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 394          * @return bool Success
 395          * @throws InvalidArgumentException
 396          */
 397         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 398                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
 399         }
 400
 401         /**
 402          * @see BagOStuff::merge()
 403          *
 404          * @param string $key
 405          * @param callable $callback Callback method to be executed
 406          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 407          * @param int $attempts The amount of times to attempt a merge in case of failure
 408          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 409          * @return bool Success
 410          */
 411         final protected function mergeViaCas( $key, callable $callback, $exptime, $attempts, $flags ) {
 412                 do {
 413                         $casToken = null; // passed by reference
 414                         // Get the old value and CAS token from cache
 415                         $this->clearLastError();
 416                         $currentValue = $this->resolveSegments(
 417                                 $key,
 418                                 $this->doGet( $key, self::READ_LATEST, $casToken )
 419                         );
 420                         if ( $this->getLastError() ) {
 421                                 $this->logger->warning(
 422                                         __METHOD__ . ' failed due to I/O error on get() for {key}.',
 423                                         [ 'key' => $key ]
 424                                 );
 425
 426                                 return false; // don't spam retries (retry only on races)
 427                         }
 428
 429                         // Derive the new value from the old value
 430                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 431                         $hadNoCurrentValue = ( $currentValue === false );
 432                         unset( $currentValue ); // free RAM in case the value is large
 433
 434                         $this->clearLastError();
 435                         if ( $value === false ) {
 436                                 $success = true; // do nothing
 437                         } elseif ( $hadNoCurrentValue ) {
 438                                 // Try to create the key, failing if it gets created in the meantime
 439                                 $success = $this->add( $key, $value, $exptime, $flags );
 440                         } else {
 441                                 // Try to update the key, failing if it gets changed in the meantime
 442                                 $success = $this->cas( $casToken, $key, $value, $exptime, $flags );
 443                         }
 444                         if ( $this->getLastError() ) {
 445                                 $this->logger->warning(
 446                                         __METHOD__ . ' failed due to I/O error for {key}.',
 447                                         [ 'key' => $key ]
 448                                 );
 449
 450                                 return false; // IO error; don't spam retries
 451                         }
 452
 453                 } while ( !$success && --$attempts );
 454
 455                 return $success;
 456         }
 457
 458         /**
 459          * Check and set an item
 460          *
 461          * @param mixed $casToken
 462          * @param string $key
 463          * @param mixed $value
 464          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 465          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 466          * @return bool Success
 467          */
 468         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 469                 if ( !$this->lock( $key, 0 ) ) {
 470                         return false; // non-blocking
 471                 }
 472
 473                 $curCasToken = null; // passed by reference
 474                 $this->doGet( $key, self::READ_LATEST, $curCasToken );
 475                 if ( $casToken === $curCasToken ) {
 476                         $success = $this->set( $key, $value, $exptime, $flags );
 477                 } else {
 478                         $this->logger->info(
 479                                 __METHOD__ . ' failed due to race condition for {key}.',
 480                                 [ 'key' => $key ]
 481                         );
 482
 483                         $success = false; // mismatched or failed
 484                 }
 485
 486                 $this->unlock( $key );
 487
 488                 return $success;
 489         }
 490
 491         /**
 492          * Change the expiration on a key if it exists
 493          *
 494          * If an expiry in the past is given then the key will immediately be expired
 495          *
 496          * For large values written using WRITE_ALLOW_SEGMENTS, this only changes the TTL of the
 497          * main segment list key. While lowering the TTL of the segment list key has the effect of
 498          * functionally lowering the TTL of the key, it might leave unused blobs in cache for longer.
 499          * Raising the TTL of such keys is not effective, since the expiration of a single segment
 500          * key effectively expires the entire value.
 501          *
 502          * @param string $key
 503          * @param int $exptime TTL or UNIX timestamp
 504          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 505          * @return bool Success Returns false on failure or if the item does not exist
 506          * @since 1.28
 507          */
 508         public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 509                 return $this->doChangeTTL( $key, $exptime, $flags );
 510         }
 511
 512         /**
 513          * @param string $key
 514          * @param int $exptime
 515          * @param int $flags
 516          * @return bool
 517          */
 518         protected function doChangeTTL( $key, $exptime, $flags ) {
 519                 $expiry = $this->convertToExpiry( $exptime );
 520                 $delete = ( $expiry != 0 && $expiry < $this->getCurrentTime() );
 521
 522                 if ( !$this->lock( $key, 0 ) ) {
 523                         return false;
 524                 }
 525                 // Use doGet() to avoid having to trigger resolveSegments()
 526                 $blob = $this->doGet( $key, self::READ_LATEST );
 527                 if ( $blob ) {
 528                         if ( $delete ) {
 529                                 $ok = $this->doDelete( $key, $flags );
 530                         } else {
 531                                 $ok = $this->doSet( $key, $blob, $exptime, $flags );
 532                         }
 533                 } else {
 534                         $ok = false;
 535                 }
 536
 537                 $this->unlock( $key );
 538
 539                 return $ok;
 540         }
 541
 542         /**
 543          * Acquire an advisory lock on a key string
 544          *
 545          * Note that if reentry is enabled, duplicate calls ignore $expiry
 546          *
 547          * @param string $key
 548          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 549          * @param int $expiry Lock expiry [optional]; 1 day maximum
 550          * @param string $rclass Allow reentry if set and the current lock used this value
 551          * @return bool Success
 552          */
 553         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 554                 // Avoid deadlocks and allow lock reentry if specified
 555                 if ( isset( $this->locks[$key] ) ) {
 556                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 557                                 ++$this->locks[$key]['depth'];
 558                                 return true;
 559                         } else {
 560                                 return false;
 561                         }
 562                 }
 563
 564                 $fname = __METHOD__;
 565                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 566                 $loop = new WaitConditionLoop(
 567                         function () use ( $key, $expiry, $fname ) {
 568                                 $this->clearLastError();
 569                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 570                                         return WaitConditionLoop::CONDITION_REACHED; // locked!
 571                                 } elseif ( $this->getLastError() ) {
 572                                         $this->logger->warning(
 573                                                 $fname . ' failed due to I/O error for {key}.',
 574                                                 [ 'key' => $key ]
 575                                         );
 576
 577                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 578                                 }
 579
 580                                 return WaitConditionLoop::CONDITION_CONTINUE;
 581                         },
 582                         $timeout
 583                 );
 584
 585                 $code = $loop->invoke();
 586                 $locked = ( $code === $loop::CONDITION_REACHED );
 587                 if ( $locked ) {
 588                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 589                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 590                         $this->logger->warning(
 591                                 "$fname failed due to timeout for {key}.",
 592                                 [ 'key' => $key, 'timeout' => $timeout ]
 593                         );
 594                 }
 595
 596                 return $locked;
 597         }
 598
 599         /**
 600          * Release an advisory lock on a key string
 601          *
 602          * @param string $key
 603          * @return bool Success
 604          */
 605         public function unlock( $key ) {
 606                 if ( !isset( $this->locks[$key] ) ) {
 607                         return false;
 608                 }
 609
 610                 if ( --$this->locks[$key]['depth'] <= 0 ) {
 611                         unset( $this->locks[$key] );
 612
 613                         $ok = $this->doDelete( "{$key}:lock" );
 614                         if ( !$ok ) {
 615                                 $this->logger->warning(
 616                                         __METHOD__ . ' failed to release lock for {key}.',
 617                                         [ 'key' => $key ]
 618                                 );
 619                         }
 620
 621                         return $ok;
 622                 }
 623
 624                 return true;
 625         }
 626
 627         /**
 628          * Get a lightweight exclusive self-unlocking lock
 629          *
 630          * Note that the same lock cannot be acquired twice.
 631          *
 632          * This is useful for task de-duplication or to avoid obtrusive
 633          * (though non-corrupting) DB errors like INSERT key conflicts
 634          * or deadlocks when using LOCK IN SHARE MODE.
 635          *
 636          * @param string $key
 637          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 638          * @param int $expiry Lock expiry [optional]; 1 day maximum
 639          * @param string $rclass Allow reentry if set and the current lock used this value
 640          * @return ScopedCallback|null Returns null on failure
 641          * @since 1.26
 642          */
 643         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 644                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 645
 646                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 647                         return null;
 648                 }
 649
 650                 $lSince = $this->getCurrentTime(); // lock timestamp
 651
 652                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 653                         $latency = 0.050; // latency skew (err towards keeping lock present)
 654                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 655                         if ( ( $age + $latency ) >= $expiry ) {
 656                                 $this->logger->warning(
 657                                         "Lock for {key} held too long ({age} sec).",
 658                                         [ 'key' => $key, 'age' => $age ]
 659                                 );
 660                                 return; // expired; it's not "safe" to delete the key
 661                         }
 662                         $this->unlock( $key );
 663                 } );
 664         }
 665
 666         /**
 667          * Delete all objects expiring before a certain date.
 668          * @param string|int $timestamp The reference date in MW or TS_UNIX format
 669          * @param callable|null $progress Optional, a function which will be called
 670          *     regularly during long-running operations with the percentage progress
 671          *     as the first parameter. [optional]
 672          * @param int $limit Maximum number of keys to delete [default: INF]
 673          *
 674          * @return bool Success; false if unimplemented
 675          */
 676         public function deleteObjectsExpiringBefore(
 677                 $timestamp,
 678                 callable $progress = null,
 679                 $limit = INF
 680         ) {
 681                 return false;
 682         }
 683
 684         /**
 685          * Get an associative array containing the item for each of the keys that have items.
 686          * @param string[] $keys List of keys; can be a map of (unused => key) for convenience
 687          * @param int $flags Bitfield; supports READ_LATEST [optional]
 688          * @return mixed[] Map of (key => value) for existing keys; preserves the order of $keys
 689          */
 690         public function getMulti( array $keys, $flags = 0 ) {
 691                 $foundByKey = $this->doGetMulti( $keys, $flags );
 692
 693                 $res = [];
 694                 foreach ( $keys as $key ) {
 695                         // Resolve one blob at a time (avoids too much I/O at once)
 696                         if ( array_key_exists( $key, $foundByKey ) ) {
 697                                 // A value should not appear in the key if a segment is missing
 698                                 $value = $this->resolveSegments( $key, $foundByKey[$key] );
 699                                 if ( $value !== false ) {
 700                                         $res[$key] = $value;
 701                                 }
 702                         }
 703                 }
 704
 705                 return $res;
 706         }
 707
 708         /**
 709          * Get an associative array containing the item for each of the keys that have items.
 710          * @param string[] $keys List of keys
 711          * @param int $flags Bitfield; supports READ_LATEST [optional]
 712          * @return mixed[] Map of (key => value) for existing keys
 713          */
 714         protected function doGetMulti( array $keys, $flags = 0 ) {
 715                 $res = [];
 716                 foreach ( $keys as $key ) {
 717                         $val = $this->doGet( $key, $flags );
 718                         if ( $val !== false ) {
 719                                 $res[$key] = $val;
 720                         }
 721                 }
 722
 723                 return $res;
 724         }
 725
 726         /**
 727          * Batch insertion/replace
 728          *
 729          * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
 730          *
 731          * WRITE_BACKGROUND can be used for bulk insertion where the response is not vital
 732          *
 733          * @param mixed[] $data Map of (key => value)
 734          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 735          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 736          * @return bool Success
 737          * @since 1.24
 738          */
 739         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 740                 if ( ( $flags & self::WRITE_ALLOW_SEGMENTS ) === self::WRITE_ALLOW_SEGMENTS ) {
 741                         throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
 742                 }
 743                 return $this->doSetMulti( $data, $exptime, $flags );
 744         }
 745
 746         /**
 747          * @param mixed[] $data Map of (key => value)
 748          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 749          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 750          * @return bool Success
 751          */
 752         protected function doSetMulti( array $data, $exptime = 0, $flags = 0 ) {
 753                 $res = true;
 754                 foreach ( $data as $key => $value ) {
 755                         $res = $this->doSet( $key, $value, $exptime, $flags ) && $res;
 756                 }
 757                 return $res;
 758         }
 759
 760         /**
 761          * Batch deletion
 762          *
 763          * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
 764          *
 765          * WRITE_BACKGROUND can be used for bulk deletion where the response is not vital
 766          *
 767          * @param string[] $keys List of keys
 768          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 769          * @return bool Success
 770          * @since 1.33
 771          */
 772         public function deleteMulti( array $keys, $flags = 0 ) {
 773                 if ( ( $flags & self::WRITE_ALLOW_SEGMENTS ) === self::WRITE_ALLOW_SEGMENTS ) {
 774                         throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
 775                 }
 776                 return $this->doDeleteMulti( $keys, $flags );
 777         }
 778
 779         /**
 780          * @param string[] $keys List of keys
 781          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 782          * @return bool Success
 783          */
 784         protected function doDeleteMulti( array $keys, $flags = 0 ) {
 785                 $res = true;
 786                 foreach ( $keys as $key ) {
 787                         $res = $this->doDelete( $key, $flags ) && $res;
 788                 }
 789                 return $res;
 790         }
 791
 792         /**
 793          * Change the expiration of multiple keys that exist
 794          *
 795          * @see BagOStuff::changeTTL()
 796          *
 797          * @param string[] $keys List of keys
 798          * @param int $exptime TTL or UNIX timestamp
 799          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 800          * @return bool Success
 801          * @since 1.34
 802          */
 803         public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
 804                 $res = true;
 805                 foreach ( $keys as $key ) {
 806                         $res = $this->doChangeTTL( $key, $exptime, $flags ) && $res;
 807                 }
 808
 809                 return $res;
 810         }
 811
 812         /**
 813          * Increase stored value of $key by $value while preserving its TTL
 814          * @param string $key Key to increase
 815          * @param int $value Value to add to $key (default: 1) [optional]
 816          * @return int|bool New value or false on failure
 817          */
 818         abstract public function incr( $key, $value = 1 );
 819
 820         /**
 821          * Decrease stored value of $key by $value while preserving its TTL
 822          * @param string $key
 823          * @param int $value Value to subtract from $key (default: 1) [optional]
 824          * @return int|bool New value or false on failure
 825          */
 826         public function decr( $key, $value = 1 ) {
 827                 return $this->incr( $key, - $value );
 828         }
 829
 830         /**
 831          * Increase stored value of $key by $value while preserving its TTL
 832          *
 833          * This will create the key with value $init and TTL $ttl instead if not present
 834          *
 835          * @param string $key
 836          * @param int $ttl
 837          * @param int $value
 838          * @param int $init
 839          * @return int|bool New value or false on failure
 840          * @since 1.24
 841          */
 842         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 843                 $this->clearLastError();
 844                 $newValue = $this->incr( $key, $value );
 845                 if ( $newValue === false && !$this->getLastError() ) {
 846                         // No key set; initialize
 847                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 848                         if ( $newValue === false && !$this->getLastError() ) {
 849                                 // Raced out initializing; increment
 850                                 $newValue = $this->incr( $key, $value );
 851                         }
 852                 }
 853
 854                 return $newValue;
 855         }
 856
 857         /**
 858          * Get and reassemble the chunks of blob at the given key
 859          *
 860          * @param string $key
 861          * @param mixed $mainValue
 862          * @return string|null|bool The combined string, false if missing, null on error
 863          */
 864         final protected function resolveSegments( $key, $mainValue ) {
 865                 if ( SerializedValueContainer::isUnified( $mainValue ) ) {
 866                         return $this->unserialize( $mainValue->{SerializedValueContainer::UNIFIED_DATA} );
 867                 }
 868
 869                 if ( SerializedValueContainer::isSegmented( $mainValue ) ) {
 870                         $orderedKeys = array_map(
 871                                 function ( $segmentHash ) use ( $key ) {
 872                                         return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
 873                                 },
 874                                 $mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
 875                         );
 876
 877                         $segmentsByKey = $this->doGetMulti( $orderedKeys );
 878
 879                         $parts = [];
 880                         foreach ( $orderedKeys as $segmentKey ) {
 881                                 if ( isset( $segmentsByKey[$segmentKey] ) ) {
 882                                         $parts[] = $segmentsByKey[$segmentKey];
 883                                 } else {
 884                                         return false; // missing segment
 885                                 }
 886                         }
 887
 888                         return $this->unserialize( implode( '', $parts ) );
 889                 }
 890
 891                 return $mainValue;
 892         }
 893
 894         /**
 895          * Get the "last error" registered; clearLastError() should be called manually
 896          * @return int ERR_* constant for the "last error" registry
 897          * @since 1.23
 898          */
 899         public function getLastError() {
 900                 return $this->lastError;
 901         }
 902
 903         /**
 904          * Clear the "last error" registry
 905          * @since 1.23
 906          */
 907         public function clearLastError() {
 908                 $this->lastError = self::ERR_NONE;
 909         }
 910
 911         /**
 912          * Set the "last error" registry
 913          * @param int $err ERR_* constant
 914          * @since 1.23
 915          */
 916         protected function setLastError( $err ) {
 917                 $this->lastError = $err;
 918         }
 919
 920         /**
 921          * Let a callback be run to avoid wasting time on special blocking calls
 922          *
 923          * The callbacks may or may not be called ever, in any particular order.
 924          * They are likely to be invoked when something WRITE_SYNC is used used.
 925          * They should follow a caching pattern as shown below, so that any code
 926          * using the work will get it's result no matter what happens.
 927          * @code
 928          *     $result = null;
 929          *     $workCallback = function () use ( &$result ) {
 930          *         if ( !$result ) {
 931          *             $result = ....
 932          *         }
 933          *         return $result;
 934          *     }
 935          * @endcode
 936          *
 937          * @param callable $workCallback
 938          * @since 1.28
 939          */
 940         final public function addBusyCallback( callable $workCallback ) {
 941                 $this->busyCallbacks[] = $workCallback;
 942         }
 943
 944         /**
 945          * @param string $text
 946          */
 947         protected function debug( $text ) {
 948                 if ( $this->debugMode ) {
 949                         $this->logger->debug( "{class} debug: $text", [ 'class' => static::class ] );
 950                 }
 951         }
 952
 953         /**
 954          * @param int $exptime
 955          * @return bool
 956          */
 957         final protected function expiryIsRelative( $exptime ) {
 958                 return ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) );
 959         }
 960
 961         /**
 962          * Convert an optionally relative timestamp to an absolute time
 963          *
 964          * The input value will be cast to an integer and interpreted as follows:
 965          *   - zero: no expiry; return zero (e.g. TTL_INDEFINITE)
 966          *   - negative: relative TTL; return UNIX timestamp offset by this value
 967          *   - positive (< 10 years): relative TTL; return UNIX timestamp offset by this value
 968          *   - positive (>= 10 years): absolute UNIX timestamp; return this value
 969          *
 970          * @param int $exptime Absolute TTL or 0 for indefinite
 971          * @return int
 972          */
 973         final protected function convertToExpiry( $exptime ) {
 974                 return $this->expiryIsRelative( $exptime )
 975                         ? (int)$this->getCurrentTime() + $exptime
 976                         : $exptime;
 977         }
 978
 979         /**
 980          * Convert an optionally absolute expiry time to a relative time. If an
 981          * absolute time is specified which is in the past, use a short expiry time.
 982          *
 983          * @param int $exptime
 984          * @return int
 985          */
 986         final protected function convertToRelative( $exptime ) {
 987                 return $this->expiryIsRelative( $exptime )
 988                         ? (int)$exptime
 989                         : max( $exptime - (int)$this->getCurrentTime(), 1 );
 990         }
 991
 992         /**
 993          * Check if a value is an integer
 994          *
 995          * @param mixed $value
 996          * @return bool
 997          */
 998         final protected function isInteger( $value ) {
 999                 if ( is_int( $value ) ) {
1000                         return true;
1001                 } elseif ( !is_string( $value ) ) {
1002                         return false;
1003                 }
1004
1005                 $integer = (int)$value;
1006
1007                 return ( $value === (string)$integer );
1008         }
1009
1010         /**
1011          * Construct a cache key.
1012          *
1013          * @since 1.27
1014          * @param string $keyspace
1015          * @param array $args
1016          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1017          */
1018         public function makeKeyInternal( $keyspace, $args ) {
1019                 $key = $keyspace;
1020                 foreach ( $args as $arg ) {
1021                         $key .= ':' . str_replace( ':', '%3A', $arg );
1022                 }
1023                 return strtr( $key, ' ', '_' );
1024         }
1025
1026         /**
1027          * Make a global cache key.
1028          *
1029          * @since 1.27
1030          * @param string $class Key class
1031          * @param string|null $component [optional] Key component (starting with a key collection name)
1032          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1033          */
1034         public function makeGlobalKey( $class, $component = null ) {
1035                 return $this->makeKeyInternal( 'global', func_get_args() );
1036         }
1037
1038         /**
1039          * Make a cache key, scoped to this instance's keyspace.
1040          *
1041          * @since 1.27
1042          * @param string $class Key class
1043          * @param string|null $component [optional] Key component (starting with a key collection name)
1044          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1045          */
1046         public function makeKey( $class, $component = null ) {
1047                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
1048         }
1049
1050         /**
1051          * @param int $flag ATTR_* class constant
1052          * @return int QOS_* class constant
1053          * @since 1.28
1054          */
1055         public function getQoS( $flag ) {
1056                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
1057         }
1058
1059         /**
1060          * @return int|float The chunk size, in bytes, of segmented objects (INF for no limit)
1061          * @since 1.34
1062          */
1063         public function getSegmentationSize() {
1064                 return $this->segmentationSize;
1065         }
1066
1067         /**
1068          * @return int|float Maximum total segmented object size in bytes (INF for no limit)
1069          * @since 1.34
1070          */
1071         public function getSegmentedValueMaxSize() {
1072                 return $this->segmentedValueMaxSize;
1073         }
1074
1075         /**
1076          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
1077          *
1078          * @param BagOStuff[] $bags
1079          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
1080          */
1081         final protected function mergeFlagMaps( array $bags ) {
1082                 $map = [];
1083                 foreach ( $bags as $bag ) {
1084                         foreach ( $bag->attrMap as $attr => $rank ) {
1085                                 if ( isset( $map[$attr] ) ) {
1086                                         $map[$attr] = min( $map[$attr], $rank );
1087                                 } else {
1088                                         $map[$attr] = $rank;
1089                                 }
1090                         }
1091                 }
1092
1093                 return $map;
1094         }
1095
1096         /**
1097          * @internal For testing only
1098          * @return float UNIX timestamp
1099          * @codeCoverageIgnore
1100          */
1101         public function getCurrentTime() {
1102                 return $this->wallClockOverride ?: microtime( true );
1103         }
1104
1105         /**
1106          * @internal For testing only
1107          * @param float|null &$time Mock UNIX timestamp
1108          * @codeCoverageIgnore
1109          */
1110         public function setMockTime( &$time ) {
1111                 $this->wallClockOverride =& $time;
1112         }
1113
1114         /**
1115          * @param mixed $value
1116          * @return string|int String/integer representation
1117          * @note Special handling is usually needed for integers so incr()/decr() work
1118          */
1119         protected function serialize( $value ) {
1120                 return is_int( $value ) ? $value : serialize( $value );
1121         }
1122
1123         /**
1124          * @param string|int $value
1125          * @return mixed Original value or false on error
1126          * @note Special handling is usually needed for integers so incr()/decr() work
1127          */
1128         protected function unserialize( $value ) {
1129                 return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
1130         }
1131 }