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() */
 101         const READ_LATEST = 1; // use latest data for replicated stores
 102         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
 103         /** Bitfield constants for set()/merge() */
 104         const WRITE_SYNC = 4; // synchronously write to all locations for replicated stores
 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 partition segments of the value
 108
 109         /** @var string Component to use for key construction of blob segment keys */
 110         const SEGMENT_COMPONENT = 'segment';
 111
 112         /**
 113          * $params include:
 114          *   - logger: Psr\Log\LoggerInterface instance
 115          *   - keyspace: Default keyspace for $this->makeKey()
 116          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
 117          *      In CLI mode, it should run the task immediately.
 118          *   - reportDupes: Whether to emit warning log messages for all keys that were
 119          *      requested more than once (requires an asyncHandler).
 120          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
 121          *   - segmentationSize: The chunk size, in bytes, of segmented values. The value should
 122          *      not exceed the maximum size of values in the storage backend, as configured by
 123          *      the site administrator.
 124          *   - segmentedValueMaxSize: The maximum total size, in bytes, of segmented values.
 125          *      This should be configured to a reasonable size give the site traffic and the
 126          *      amount of I/O between application and cache servers that the network can handle.
 127          * @param array $params
 128          */
 129         public function __construct( array $params = [] ) {
 130                 $this->setLogger( $params['logger'] ?? new NullLogger() );
 131
 132                 if ( isset( $params['keyspace'] ) ) {
 133                         $this->keyspace = $params['keyspace'];
 134                 }
 135
 136                 $this->asyncHandler = $params['asyncHandler'] ?? null;
 137
 138                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 139                         $this->reportDupes = true;
 140                 }
 141
 142                 $this->syncTimeout = $params['syncTimeout'] ?? 3;
 143                 $this->segmentationSize = $params['segmentationSize'] ?? 8388608; // 8MiB
 144                 $this->segmentedValueMaxSize = $params['segmentedValueMaxSize'] ?? 67108864; // 64MiB
 145         }
 146
 147         /**
 148          * @param LoggerInterface $logger
 149          * @return void
 150          */
 151         public function setLogger( LoggerInterface $logger ) {
 152                 $this->logger = $logger;
 153         }
 154
 155         /**
 156          * @param bool $bool
 157          */
 158         public function setDebug( $bool ) {
 159                 $this->debugMode = $bool;
 160         }
 161
 162         /**
 163          * Get an item with the given key, regenerating and setting it if not found
 164          *
 165          * Nothing is stored nor deleted if the callback returns false
 166          *
 167          * @param string $key
 168          * @param int $ttl Time-to-live (seconds)
 169          * @param callable $callback Callback that derives the new value
 170          * @param int $flags Bitfield of BagOStuff::READ_* or BagOStuff::WRITE_* constants [optional]
 171          * @return mixed The cached value if found or the result of $callback otherwise
 172          * @since 1.27
 173          */
 174         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 175                 $value = $this->get( $key, $flags );
 176
 177                 if ( $value === false ) {
 178                         if ( !is_callable( $callback ) ) {
 179                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 180                         }
 181                         $value = call_user_func( $callback );
 182                         if ( $value !== false ) {
 183                                 $this->set( $key, $value, $ttl, $flags );
 184                         }
 185                 }
 186
 187                 return $value;
 188         }
 189
 190         /**
 191          * Get an item with the given key
 192          *
 193          * If the key includes a deterministic input hash (e.g. the key can only have
 194          * the correct value) or complete staleness checks are handled by the caller
 195          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 196          * This lets tiered backends know they can safely upgrade a cached value to
 197          * higher tiers using standard TTLs.
 198          *
 199          * @param string $key
 200          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 201          * @return mixed Returns false on failure or if the item does not exist
 202          */
 203         public function get( $key, $flags = 0 ) {
 204                 $this->trackDuplicateKeys( $key );
 205
 206                 return $this->resolveSegments( $key, $this->doGet( $key, $flags ) );
 207         }
 208
 209         /**
 210          * Track the number of times that a given key has been used.
 211          * @param string $key
 212          */
 213         private function trackDuplicateKeys( $key ) {
 214                 if ( !$this->reportDupes ) {
 215                         return;
 216                 }
 217
 218                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 219                         // Track that we have seen this key. This N-1 counting style allows
 220                         // easy filtering with array_filter() later.
 221                         $this->duplicateKeyLookups[$key] = 0;
 222                 } else {
 223                         $this->duplicateKeyLookups[$key] += 1;
 224
 225                         if ( $this->dupeTrackScheduled === false ) {
 226                                 $this->dupeTrackScheduled = true;
 227                                 // Schedule a callback that logs keys processed more than once by get().
 228                                 call_user_func( $this->asyncHandler, function () {
 229                                         $dups = array_filter( $this->duplicateKeyLookups );
 230                                         foreach ( $dups as $key => $count ) {
 231                                                 $this->logger->warning(
 232                                                         'Duplicate get(): "{key}" fetched {count} times',
 233                                                         // Count is N-1 of the actual lookup count
 234                                                         [ 'key' => $key, 'count' => $count + 1, ]
 235                                                 );
 236                                         }
 237                                 } );
 238                         }
 239                 }
 240         }
 241
 242         /**
 243          * @param string $key
 244          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 245          * @param mixed|null &$casToken Token to use for check-and-set comparisons
 246          * @return mixed Returns false on failure or if the item does not exist
 247          */
 248         abstract protected function doGet( $key, $flags = 0, &$casToken = null );
 249
 250         /**
 251          * Set an item
 252          *
 253          * @param string $key
 254          * @param mixed $value
 255          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 256          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 257          * @return bool Success
 258          */
 259         public function set( $key, $value, $exptime = 0, $flags = 0 ) {
 260                 if (
 261                         is_int( $value ) || // avoid breaking incr()/decr()
 262                         ( $flags & self::WRITE_ALLOW_SEGMENTS ) != self::WRITE_ALLOW_SEGMENTS ||
 263                         is_infinite( $this->segmentationSize )
 264                 ) {
 265                         return $this->doSet( $key, $value, $exptime, $flags );
 266                 }
 267
 268                 $serialized = $this->serialize( $value );
 269                 $segmentSize = $this->getSegmentationSize();
 270                 $maxTotalSize = $this->getSegmentedValueMaxSize();
 271
 272                 $size = strlen( $serialized );
 273                 if ( $size <= $segmentSize ) {
 274                         // Since the work of serializing it was already done, just use it inline
 275                         return $this->doSet(
 276                                 $key,
 277                                 SerializedValueContainer::newUnified( $serialized ),
 278                                 $exptime,
 279                                 $flags
 280                         );
 281                 } elseif ( $size > $maxTotalSize ) {
 282                         $this->setLastError( "Key $key exceeded $maxTotalSize bytes." );
 283
 284                         return false;
 285                 }
 286
 287                 $chunksByKey = [];
 288                 $segmentHashes = [];
 289                 $count = intdiv( $size, $segmentSize ) + ( ( $size % $segmentSize ) ? 1 : 0 );
 290                 for ( $i = 0; $i < $count; ++$i ) {
 291                         $segment = substr( $serialized, $i * $segmentSize, $segmentSize );
 292                         $hash = sha1( $segment );
 293                         $chunkKey = $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $hash );
 294                         $chunksByKey[$chunkKey] = $segment;
 295                         $segmentHashes[] = $hash;
 296                 }
 297
 298                 $flags &= ~self::WRITE_ALLOW_SEGMENTS; // sanity
 299                 $ok = $this->setMulti( $chunksByKey, $exptime, $flags );
 300                 if ( $ok ) {
 301                         // Only when all segments are stored should the main key be changed
 302                         $ok = $this->doSet(
 303                                 $key,
 304                                 SerializedValueContainer::newSegmented( $segmentHashes ),
 305                                 $exptime,
 306                                 $flags
 307                         );
 308                 }
 309
 310                 return $ok;
 311         }
 312
 313         /**
 314          * Set an item
 315          *
 316          * @param string $key
 317          * @param mixed $value
 318          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 319          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 320          * @return bool Success
 321          */
 322         abstract protected function doSet( $key, $value, $exptime = 0, $flags = 0 );
 323
 324         /**
 325          * Delete an item
 326          *
 327          * For large values written using WRITE_ALLOW_SEGMENTS, this only deletes the main
 328          * segment list key unless WRITE_PRUNE_SEGMENTS is in the flags. While deleting the segment
 329          * list key has the effect of functionally deleting the key, it leaves unused blobs in cache.
 330          *
 331          * @param string $key
 332          * @return bool True if the item was deleted or not found, false on failure
 333          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 334          */
 335         public function delete( $key, $flags = 0 ) {
 336                 if ( ( $flags & self::WRITE_PRUNE_SEGMENTS ) != self::WRITE_PRUNE_SEGMENTS ) {
 337                         return $this->doDelete( $key, $flags );
 338                 }
 339
 340                 $mainValue = $this->doGet( $key, self::READ_LATEST );
 341                 if ( !$this->doDelete( $key, $flags ) ) {
 342                         return false;
 343                 }
 344
 345                 if ( !SerializedValueContainer::isSegmented( $mainValue ) ) {
 346                         return true; // no segments to delete
 347                 }
 348
 349                 $orderedKeys = array_map(
 350                         function ( $segmentHash ) use ( $key ) {
 351                                 return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
 352                         },
 353                         $mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
 354                 );
 355
 356                 return $this->deleteMulti( $orderedKeys, $flags );
 357         }
 358
 359         /**
 360          * Delete an item
 361          *
 362          * @param string $key
 363          * @return bool True if the item was deleted or not found, false on failure
 364          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 365          */
 366         abstract protected function doDelete( $key, $flags = 0 );
 367
 368         /**
 369          * Insert an item if it does not already exist
 370          *
 371          * @param string $key
 372          * @param mixed $value
 373          * @param int $exptime
 374          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 375          * @return bool Success
 376          */
 377         abstract public function add( $key, $value, $exptime = 0, $flags = 0 );
 378
 379         /**
 380          * Merge changes into the existing cache value (possibly creating a new one)
 381          *
 382          * The callback function returns the new value given the current value
 383          * (which will be false if not present), and takes the arguments:
 384          * (this BagOStuff, cache key, current value, TTL).
 385          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 386          * Nothing is stored nor deleted if the callback returns false.
 387          *
 388          * @param string $key
 389          * @param callable $callback Callback method to be executed
 390          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 391          * @param int $attempts The amount of times to attempt a merge in case of failure
 392          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 393          * @return bool Success
 394          * @throws InvalidArgumentException
 395          */
 396         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 397                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
 398         }
 399
 400         /**
 401          * @see BagOStuff::merge()
 402          *
 403          * @param string $key
 404          * @param callable $callback Callback method to be executed
 405          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 406          * @param int $attempts The amount of times to attempt a merge in case of failure
 407          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 408          * @return bool Success
 409          */
 410         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 411                 do {
 412                         $casToken = null; // passed by reference
 413                         // Get the old value and CAS token from cache
 414                         $this->clearLastError();
 415                         $currentValue = $this->resolveSegments(
 416                                 $key,
 417                                 $this->doGet( $key, self::READ_LATEST, $casToken )
 418                         );
 419                         if ( $this->getLastError() ) {
 420                                 $this->logger->warning(
 421                                         __METHOD__ . ' failed due to I/O error on get() for {key}.',
 422                                         [ 'key' => $key ]
 423                                 );
 424
 425                                 return false; // don't spam retries (retry only on races)
 426                         }
 427
 428                         // Derive the new value from the old value
 429                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 430                         $hadNoCurrentValue = ( $currentValue === false );
 431                         unset( $currentValue ); // free RAM in case the value is large
 432
 433                         $this->clearLastError();
 434                         if ( $value === false ) {
 435                                 $success = true; // do nothing
 436                         } elseif ( $hadNoCurrentValue ) {
 437                                 // Try to create the key, failing if it gets created in the meantime
 438                                 $success = $this->add( $key, $value, $exptime, $flags );
 439                         } else {
 440                                 // Try to update the key, failing if it gets changed in the meantime
 441                                 $success = $this->cas( $casToken, $key, $value, $exptime, $flags );
 442                         }
 443                         if ( $this->getLastError() ) {
 444                                 $this->logger->warning(
 445                                         __METHOD__ . ' failed due to I/O error for {key}.',
 446                                         [ 'key' => $key ]
 447                                 );
 448
 449                                 return false; // IO error; don't spam retries
 450                         }
 451
 452                 } while ( !$success && --$attempts );
 453
 454                 return $success;
 455         }
 456
 457         /**
 458          * Check and set an item
 459          *
 460          * @param mixed $casToken
 461          * @param string $key
 462          * @param mixed $value
 463          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 464          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 465          * @return bool Success
 466          */
 467         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 468                 if ( !$this->lock( $key, 0 ) ) {
 469                         return false; // non-blocking
 470                 }
 471
 472                 $curCasToken = null; // passed by reference
 473                 $this->doGet( $key, self::READ_LATEST, $curCasToken );
 474                 if ( $casToken === $curCasToken ) {
 475                         $success = $this->set( $key, $value, $exptime, $flags );
 476                 } else {
 477                         $this->logger->info(
 478                                 __METHOD__ . ' failed due to race condition for {key}.',
 479                                 [ 'key' => $key ]
 480                         );
 481
 482                         $success = false; // mismatched or failed
 483                 }
 484
 485                 $this->unlock( $key );
 486
 487                 return $success;
 488         }
 489
 490         /**
 491          * Change the expiration on a key if it exists
 492          *
 493          * If an expiry in the past is given then the key will immediately be expired
 494          *
 495          * For large values written using WRITE_ALLOW_SEGMENTS, this only changes the TTL of the
 496          * main segment list key. While lowering the TTL of the segment list key has the effect of
 497          * functionally lowering the TTL of the key, it might leave unused blobs in cache for longer.
 498          * Raising the TTL of such keys is not effective, since the expiration of a single segment
 499          * key effectively expires the entire value.
 500          *
 501          * @param string $key
 502          * @param int $exptime TTL or UNIX timestamp
 503          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 504          * @return bool Success Returns false on failure or if the item does not exist
 505          * @since 1.28
 506          */
 507         public function changeTTL( $key, $exptime = 0, $flags = 0 ) {
 508                 return $this->doChangeTTL( $key, $exptime, $flags );
 509         }
 510
 511         /**
 512          * @param string $key
 513          * @param int $exptime
 514          * @param int $flags
 515          * @return bool
 516          */
 517         protected function doChangeTTL( $key, $exptime, $flags ) {
 518                 $expiry = $this->convertToExpiry( $exptime );
 519                 $delete = ( $expiry != 0 && $expiry < $this->getCurrentTime() );
 520
 521                 if ( !$this->lock( $key, 0 ) ) {
 522                         return false;
 523                 }
 524                 // Use doGet() to avoid having to trigger resolveSegments()
 525                 $blob = $this->doGet( $key, self::READ_LATEST );
 526                 if ( $blob ) {
 527                         if ( $delete ) {
 528                                 $ok = $this->doDelete( $key, $flags );
 529                         } else {
 530                                 $ok = $this->doSet( $key, $blob, $exptime, $flags );
 531                         }
 532                 } else {
 533                         $ok = false;
 534                 }
 535
 536                 $this->unlock( $key );
 537
 538                 return $ok;
 539         }
 540
 541         /**
 542          * Acquire an advisory lock on a key string
 543          *
 544          * Note that if reentry is enabled, duplicate calls ignore $expiry
 545          *
 546          * @param string $key
 547          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 548          * @param int $expiry Lock expiry [optional]; 1 day maximum
 549          * @param string $rclass Allow reentry if set and the current lock used this value
 550          * @return bool Success
 551          */
 552         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 553                 // Avoid deadlocks and allow lock reentry if specified
 554                 if ( isset( $this->locks[$key] ) ) {
 555                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 556                                 ++$this->locks[$key]['depth'];
 557                                 return true;
 558                         } else {
 559                                 return false;
 560                         }
 561                 }
 562
 563                 $fname = __METHOD__;
 564                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 565                 $loop = new WaitConditionLoop(
 566                         function () use ( $key, $expiry, $fname ) {
 567                                 $this->clearLastError();
 568                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 569                                         return WaitConditionLoop::CONDITION_REACHED; // locked!
 570                                 } elseif ( $this->getLastError() ) {
 571                                         $this->logger->warning(
 572                                                 $fname . ' failed due to I/O error for {key}.',
 573                                                 [ 'key' => $key ]
 574                                         );
 575
 576                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 577                                 }
 578
 579                                 return WaitConditionLoop::CONDITION_CONTINUE;
 580                         },
 581                         $timeout
 582                 );
 583
 584                 $code = $loop->invoke();
 585                 $locked = ( $code === $loop::CONDITION_REACHED );
 586                 if ( $locked ) {
 587                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 588                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 589                         $this->logger->warning(
 590                                 "$fname failed due to timeout for {key}.",
 591                                 [ 'key' => $key, 'timeout' => $timeout ]
 592                         );
 593                 }
 594
 595                 return $locked;
 596         }
 597
 598         /**
 599          * Release an advisory lock on a key string
 600          *
 601          * @param string $key
 602          * @return bool Success
 603          */
 604         public function unlock( $key ) {
 605                 if ( !isset( $this->locks[$key] ) ) {
 606                         return false;
 607                 }
 608
 609                 if ( --$this->locks[$key]['depth'] <= 0 ) {
 610                         unset( $this->locks[$key] );
 611
 612                         $ok = $this->doDelete( "{$key}:lock" );
 613                         if ( !$ok ) {
 614                                 $this->logger->warning(
 615                                         __METHOD__ . ' failed to release lock for {key}.',
 616                                         [ 'key' => $key ]
 617                                 );
 618                         }
 619
 620                         return $ok;
 621                 }
 622
 623                 return true;
 624         }
 625
 626         /**
 627          * Get a lightweight exclusive self-unlocking lock
 628          *
 629          * Note that the same lock cannot be acquired twice.
 630          *
 631          * This is useful for task de-duplication or to avoid obtrusive
 632          * (though non-corrupting) DB errors like INSERT key conflicts
 633          * or deadlocks when using LOCK IN SHARE MODE.
 634          *
 635          * @param string $key
 636          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 637          * @param int $expiry Lock expiry [optional]; 1 day maximum
 638          * @param string $rclass Allow reentry if set and the current lock used this value
 639          * @return ScopedCallback|null Returns null on failure
 640          * @since 1.26
 641          */
 642         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 643                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 644
 645                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 646                         return null;
 647                 }
 648
 649                 $lSince = $this->getCurrentTime(); // lock timestamp
 650
 651                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 652                         $latency = 0.050; // latency skew (err towards keeping lock present)
 653                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 654                         if ( ( $age + $latency ) >= $expiry ) {
 655                                 $this->logger->warning(
 656                                         "Lock for {key} held too long ({age} sec).",
 657                                         [ 'key' => $key, 'age' => $age ]
 658                                 );
 659                                 return; // expired; it's not "safe" to delete the key
 660                         }
 661                         $this->unlock( $key );
 662                 } );
 663         }
 664
 665         /**
 666          * Delete all objects expiring before a certain date.
 667          * @param string|int $timestamp The reference date in MW or TS_UNIX format
 668          * @param callable|null $progressCallback Optional, a function which will be called
 669          *     regularly during long-running operations with the percentage progress
 670          *     as the first parameter. [optional]
 671          * @param int $limit Maximum number of keys to delete [default: INF]
 672          *
 673          * @return bool Success, false if unimplemented
 674          */
 675         public function deleteObjectsExpiringBefore(
 676                 $timestamp,
 677                 callable $progressCallback = null,
 678                 $limit = INF
 679         ) {
 680                 // stub
 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
 687          * @param int $flags Bitfield; supports READ_LATEST [optional]
 688          * @return array Map of (key => value) for existing keys
 689          */
 690         public function getMulti( array $keys, $flags = 0 ) {
 691                 $valuesBykey = $this->doGetMulti( $keys, $flags );
 692                 foreach ( $valuesBykey as $key => $value ) {
 693                         // Resolve one blob at a time (avoids too much I/O at once)
 694                         $valuesBykey[$key] = $this->resolveSegments( $key, $value );
 695                 }
 696
 697                 return $valuesBykey;
 698         }
 699
 700         /**
 701          * Get an associative array containing the item for each of the keys that have items.
 702          * @param string[] $keys List of keys
 703          * @param int $flags Bitfield; supports READ_LATEST [optional]
 704          * @return array Map of (key => value) for existing keys
 705          */
 706         protected function doGetMulti( array $keys, $flags = 0 ) {
 707                 $res = [];
 708                 foreach ( $keys as $key ) {
 709                         $val = $this->doGet( $key, $flags );
 710                         if ( $val !== false ) {
 711                                 $res[$key] = $val;
 712                         }
 713                 }
 714
 715                 return $res;
 716         }
 717
 718         /**
 719          * Batch insertion/replace
 720          *
 721          * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
 722          *
 723          * @param mixed[] $data Map of (key => value)
 724          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 725          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 726          * @return bool Success
 727          * @since 1.24
 728          */
 729         final public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 730                 if ( ( $flags & self::WRITE_ALLOW_SEGMENTS ) === self::WRITE_ALLOW_SEGMENTS ) {
 731                         throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
 732                 }
 733
 734                 return $this->doSetMulti( $data, $exptime, $flags );
 735         }
 736
 737         /**
 738          * @param mixed[] $data Map of (key => value)
 739          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 740          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 741          * @return bool Success
 742          */
 743         protected function doSetMulti( array $data, $exptime = 0, $flags = 0 ) {
 744                 $res = true;
 745                 foreach ( $data as $key => $value ) {
 746                         $res = $this->doSet( $key, $value, $exptime, $flags ) && $res;
 747                 }
 748
 749                 return $res;
 750         }
 751
 752         /**
 753          * Batch deletion
 754          *
 755          * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
 756          *
 757          * @param string[] $keys List of keys
 758          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 759          * @return bool Success
 760          * @since 1.33
 761          */
 762         final public function deleteMulti( array $keys, $flags = 0 ) {
 763                 if ( ( $flags & self::WRITE_ALLOW_SEGMENTS ) === self::WRITE_ALLOW_SEGMENTS ) {
 764                         throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
 765                 }
 766
 767                 return $this->doDeleteMulti( $keys, $flags );
 768         }
 769
 770         /**
 771          * @param string[] $keys List of keys
 772          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 773          * @return bool Success
 774          */
 775         protected function doDeleteMulti( array $keys, $flags = 0 ) {
 776                 $res = true;
 777                 foreach ( $keys as $key ) {
 778                         $res = $this->doDelete( $key, $flags ) && $res;
 779                 }
 780
 781                 return $res;
 782         }
 783
 784         /**
 785          * Change the expiration of multiple keys that exist
 786          *
 787          * @see BagOStuff::changeTTL()
 788          *
 789          * @param string[] $keys List of keys
 790          * @param int $exptime TTL or UNIX timestamp
 791          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 792          * @return bool Success
 793          * @since 1.34
 794          */
 795         public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
 796                 $res = true;
 797                 foreach ( $keys as $key ) {
 798                         $res = $this->doChangeTTL( $key, $exptime, $flags ) && $res;
 799                 }
 800
 801                 return $res;
 802         }
 803
 804         /**
 805          * Increase stored value of $key by $value while preserving its TTL
 806          * @param string $key Key to increase
 807          * @param int $value Value to add to $key (default: 1) [optional]
 808          * @return int|bool New value or false on failure
 809          */
 810         abstract public function incr( $key, $value = 1 );
 811
 812         /**
 813          * Decrease stored value of $key by $value while preserving its TTL
 814          * @param string $key
 815          * @param int $value Value to subtract from $key (default: 1) [optional]
 816          * @return int|bool New value or false on failure
 817          */
 818         public function decr( $key, $value = 1 ) {
 819                 return $this->incr( $key, - $value );
 820         }
 821
 822         /**
 823          * Increase stored value of $key by $value while preserving its TTL
 824          *
 825          * This will create the key with value $init and TTL $ttl instead if not present
 826          *
 827          * @param string $key
 828          * @param int $ttl
 829          * @param int $value
 830          * @param int $init
 831          * @return int|bool New value or false on failure
 832          * @since 1.24
 833          */
 834         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 835                 $this->clearLastError();
 836                 $newValue = $this->incr( $key, $value );
 837                 if ( $newValue === false && !$this->getLastError() ) {
 838                         // No key set; initialize
 839                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 840                         if ( $newValue === false && !$this->getLastError() ) {
 841                                 // Raced out initializing; increment
 842                                 $newValue = $this->incr( $key, $value );
 843                         }
 844                 }
 845
 846                 return $newValue;
 847         }
 848
 849         /**
 850          * Get and reassemble the chunks of blob at the given key
 851          *
 852          * @param string $key
 853          * @param mixed $mainValue
 854          * @return string|null|bool The combined string, false if missing, null on error
 855          */
 856         protected function resolveSegments( $key, $mainValue ) {
 857                 if ( SerializedValueContainer::isUnified( $mainValue ) ) {
 858                         return $this->unserialize( $mainValue->{SerializedValueContainer::UNIFIED_DATA} );
 859                 }
 860
 861                 if ( SerializedValueContainer::isSegmented( $mainValue ) ) {
 862                         $orderedKeys = array_map(
 863                                 function ( $segmentHash ) use ( $key ) {
 864                                         return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
 865                                 },
 866                                 $mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
 867                         );
 868
 869                         $segmentsByKey = $this->doGetMulti( $orderedKeys );
 870
 871                         $parts = [];
 872                         foreach ( $orderedKeys as $segmentKey ) {
 873                                 if ( isset( $segmentsByKey[$segmentKey] ) ) {
 874                                         $parts[] = $segmentsByKey[$segmentKey];
 875                                 } else {
 876                                         return false; // missing segment
 877                                 }
 878                         }
 879
 880                         return $this->unserialize( implode( '', $parts ) );
 881                 }
 882
 883                 return $mainValue;
 884         }
 885
 886         /**
 887          * Get the "last error" registered; clearLastError() should be called manually
 888          * @return int ERR_* constant for the "last error" registry
 889          * @since 1.23
 890          */
 891         public function getLastError() {
 892                 return $this->lastError;
 893         }
 894
 895         /**
 896          * Clear the "last error" registry
 897          * @since 1.23
 898          */
 899         public function clearLastError() {
 900                 $this->lastError = self::ERR_NONE;
 901         }
 902
 903         /**
 904          * Set the "last error" registry
 905          * @param int $err ERR_* constant
 906          * @since 1.23
 907          */
 908         protected function setLastError( $err ) {
 909                 $this->lastError = $err;
 910         }
 911
 912         /**
 913          * Let a callback be run to avoid wasting time on special blocking calls
 914          *
 915          * The callbacks may or may not be called ever, in any particular order.
 916          * They are likely to be invoked when something WRITE_SYNC is used used.
 917          * They should follow a caching pattern as shown below, so that any code
 918          * using the work will get it's result no matter what happens.
 919          * @code
 920          *     $result = null;
 921          *     $workCallback = function () use ( &$result ) {
 922          *         if ( !$result ) {
 923          *             $result = ....
 924          *         }
 925          *         return $result;
 926          *     }
 927          * @endcode
 928          *
 929          * @param callable $workCallback
 930          * @since 1.28
 931          */
 932         public function addBusyCallback( callable $workCallback ) {
 933                 $this->busyCallbacks[] = $workCallback;
 934         }
 935
 936         /**
 937          * @param string $text
 938          */
 939         protected function debug( $text ) {
 940                 if ( $this->debugMode ) {
 941                         $this->logger->debug( "{class} debug: $text", [
 942                                 'class' => static::class,
 943                         ] );
 944                 }
 945         }
 946
 947         /**
 948          * @param int $exptime
 949          * @return bool
 950          */
 951         protected function expiryIsRelative( $exptime ) {
 952                 return ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) );
 953         }
 954
 955         /**
 956          * Convert an optionally relative timestamp to an absolute time
 957          *
 958          * The input value will be cast to an integer and interpreted as follows:
 959          *   - zero: no expiry; return zero (e.g. TTL_INDEFINITE)
 960          *   - negative: relative TTL; return UNIX timestamp offset by this value
 961          *   - positive (< 10 years): relative TTL; return UNIX timestamp offset by this value
 962          *   - positive (>= 10 years): absolute UNIX timestamp; return this value
 963          *
 964          * @param int $exptime Absolute TTL or 0 for indefinite
 965          * @return int
 966          */
 967         protected function convertToExpiry( $exptime ) {
 968                 $exptime = (int)$exptime; // sanity
 969
 970                 return $this->expiryIsRelative( $exptime )
 971                         ? (int)$this->getCurrentTime() + $exptime
 972                         : $exptime;
 973         }
 974
 975         /**
 976          * Convert an optionally absolute expiry time to a relative time. If an
 977          * absolute time is specified which is in the past, use a short expiry time.
 978          *
 979          * @param int $exptime
 980          * @return int
 981          */
 982         protected function convertToRelative( $exptime ) {
 983                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 984                         $exptime -= (int)$this->getCurrentTime();
 985                         if ( $exptime <= 0 ) {
 986                                 $exptime = 1;
 987                         }
 988                         return $exptime;
 989                 } else {
 990                         return $exptime;
 991                 }
 992         }
 993
 994         /**
 995          * Check if a value is an integer
 996          *
 997          * @param mixed $value
 998          * @return bool
 999          */
1000         protected function isInteger( $value ) {
1001                 if ( is_int( $value ) ) {
1002                         return true;
1003                 } elseif ( !is_string( $value ) ) {
1004                         return false;
1005                 }
1006
1007                 $integer = (int)$value;
1008
1009                 return ( $value === (string)$integer );
1010         }
1011
1012         /**
1013          * Construct a cache key.
1014          *
1015          * @since 1.27
1016          * @param string $keyspace
1017          * @param array $args
1018          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1019          */
1020         public function makeKeyInternal( $keyspace, $args ) {
1021                 $key = $keyspace;
1022                 foreach ( $args as $arg ) {
1023                         $key .= ':' . str_replace( ':', '%3A', $arg );
1024                 }
1025                 return strtr( $key, ' ', '_' );
1026         }
1027
1028         /**
1029          * Make a global cache key.
1030          *
1031          * @since 1.27
1032          * @param string $class Key class
1033          * @param string|null $component [optional] Key component (starting with a key collection name)
1034          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1035          */
1036         public function makeGlobalKey( $class, $component = null ) {
1037                 return $this->makeKeyInternal( 'global', func_get_args() );
1038         }
1039
1040         /**
1041          * Make a cache key, scoped to this instance's keyspace.
1042          *
1043          * @since 1.27
1044          * @param string $class Key class
1045          * @param string|null $component [optional] Key component (starting with a key collection name)
1046          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1047          */
1048         public function makeKey( $class, $component = null ) {
1049                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
1050         }
1051
1052         /**
1053          * @param int $flag ATTR_* class constant
1054          * @return int QOS_* class constant
1055          * @since 1.28
1056          */
1057         public function getQoS( $flag ) {
1058                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
1059         }
1060
1061         /**
1062          * @return int|float The chunk size, in bytes, of segmented objects (INF for no limit)
1063          * @since 1.34
1064          */
1065         public function getSegmentationSize() {
1066                 return $this->segmentationSize;
1067         }
1068
1069         /**
1070          * @return int|float Maximum total segmented object size in bytes (INF for no limit)
1071          * @since 1.34
1072          */
1073         public function getSegmentedValueMaxSize() {
1074                 return $this->segmentedValueMaxSize;
1075         }
1076
1077         /**
1078          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
1079          *
1080          * @param BagOStuff[] $bags
1081          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
1082          */
1083         protected function mergeFlagMaps( array $bags ) {
1084                 $map = [];
1085                 foreach ( $bags as $bag ) {
1086                         foreach ( $bag->attrMap as $attr => $rank ) {
1087                                 if ( isset( $map[$attr] ) ) {
1088                                         $map[$attr] = min( $map[$attr], $rank );
1089                                 } else {
1090                                         $map[$attr] = $rank;
1091                                 }
1092                         }
1093                 }
1094
1095                 return $map;
1096         }
1097
1098         /**
1099          * @internal For testing only
1100          * @return float UNIX timestamp
1101          * @codeCoverageIgnore
1102          */
1103         public function getCurrentTime() {
1104                 return $this->wallClockOverride ?: microtime( true );
1105         }
1106
1107         /**
1108          * @internal For testing only
1109          * @param float|null &$time Mock UNIX timestamp
1110          * @codeCoverageIgnore
1111          */
1112         public function setMockTime( &$time ) {
1113                 $this->wallClockOverride =& $time;
1114         }
1115
1116         /**
1117          * @param mixed $value
1118          * @return string|int String/integer representation
1119          * @note Special handling is usually needed for integers so incr()/decr() work
1120          */
1121         protected function serialize( $value ) {
1122                 return is_int( $value ) ? $value : serialize( $value );
1123         }
1124
1125         /**
1126          * @param string|int $value
1127          * @return mixed Original value or false on error
1128          * @note Special handling is usually needed for integers so incr()/decr() work
1129          */
1130         protected function unserialize( $value ) {
1131                 return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
1132         }
1133 }