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         final protected function mergeViaCas( $key, callable $callback, $exptime, $attempts, $flags ) {
 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 $progress 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 $progress = null,
 678                 $limit = INF
 679         ) {
 680                 return false;
 681         }
 682
 683         /**
 684          * Get an associative array containing the item for each of the keys that have items.
 685          * @param string[] $keys List of keys
 686          * @param int $flags Bitfield; supports READ_LATEST [optional]
 687          * @return array Map of (key => value) for existing keys
 688          */
 689         public function getMulti( array $keys, $flags = 0 ) {
 690                 $valuesBykey = $this->doGetMulti( $keys, $flags );
 691                 foreach ( $valuesBykey as $key => $value ) {
 692                         // Resolve one blob at a time (avoids too much I/O at once)
 693                         $valuesBykey[$key] = $this->resolveSegments( $key, $value );
 694                 }
 695
 696                 return $valuesBykey;
 697         }
 698
 699         /**
 700          * Get an associative array containing the item for each of the keys that have items.
 701          * @param string[] $keys List of keys
 702          * @param int $flags Bitfield; supports READ_LATEST [optional]
 703          * @return array Map of (key => value) for existing keys
 704          */
 705         protected function doGetMulti( array $keys, $flags = 0 ) {
 706                 $res = [];
 707                 foreach ( $keys as $key ) {
 708                         $val = $this->doGet( $key, $flags );
 709                         if ( $val !== false ) {
 710                                 $res[$key] = $val;
 711                         }
 712                 }
 713
 714                 return $res;
 715         }
 716
 717         /**
 718          * Batch insertion/replace
 719          *
 720          * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
 721          *
 722          * @param mixed[] $data Map of (key => value)
 723          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 724          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 725          * @return bool Success
 726          * @since 1.24
 727          */
 728         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 729                 if ( ( $flags & self::WRITE_ALLOW_SEGMENTS ) === self::WRITE_ALLOW_SEGMENTS ) {
 730                         throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
 731                 }
 732                 return $this->doSetMulti( $data, $exptime, $flags );
 733         }
 734
 735         /**
 736          * @param mixed[] $data Map of (key => value)
 737          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 738          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 739          * @return bool Success
 740          */
 741         protected function doSetMulti( array $data, $exptime = 0, $flags = 0 ) {
 742                 $res = true;
 743                 foreach ( $data as $key => $value ) {
 744                         $res = $this->doSet( $key, $value, $exptime, $flags ) && $res;
 745                 }
 746                 return $res;
 747         }
 748
 749         /**
 750          * Batch deletion
 751          *
 752          * This does not support WRITE_ALLOW_SEGMENTS to avoid excessive read I/O
 753          *
 754          * @param string[] $keys List of keys
 755          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 756          * @return bool Success
 757          * @since 1.33
 758          */
 759         public function deleteMulti( array $keys, $flags = 0 ) {
 760                 if ( ( $flags & self::WRITE_ALLOW_SEGMENTS ) === self::WRITE_ALLOW_SEGMENTS ) {
 761                         throw new InvalidArgumentException( __METHOD__ . ' got WRITE_ALLOW_SEGMENTS' );
 762                 }
 763                 return $this->doDeleteMulti( $keys, $flags );
 764         }
 765
 766         /**
 767          * @param string[] $keys List of keys
 768          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 769          * @return bool Success
 770          */
 771         protected function doDeleteMulti( array $keys, $flags = 0 ) {
 772                 $res = true;
 773                 foreach ( $keys as $key ) {
 774                         $res = $this->doDelete( $key, $flags ) && $res;
 775                 }
 776                 return $res;
 777         }
 778
 779         /**
 780          * Change the expiration of multiple keys that exist
 781          *
 782          * @see BagOStuff::changeTTL()
 783          *
 784          * @param string[] $keys List of keys
 785          * @param int $exptime TTL or UNIX timestamp
 786          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 787          * @return bool Success
 788          * @since 1.34
 789          */
 790         public function changeTTLMulti( array $keys, $exptime, $flags = 0 ) {
 791                 $res = true;
 792                 foreach ( $keys as $key ) {
 793                         $res = $this->doChangeTTL( $key, $exptime, $flags ) && $res;
 794                 }
 795
 796                 return $res;
 797         }
 798
 799         /**
 800          * Increase stored value of $key by $value while preserving its TTL
 801          * @param string $key Key to increase
 802          * @param int $value Value to add to $key (default: 1) [optional]
 803          * @return int|bool New value or false on failure
 804          */
 805         abstract public function incr( $key, $value = 1 );
 806
 807         /**
 808          * Decrease stored value of $key by $value while preserving its TTL
 809          * @param string $key
 810          * @param int $value Value to subtract from $key (default: 1) [optional]
 811          * @return int|bool New value or false on failure
 812          */
 813         public function decr( $key, $value = 1 ) {
 814                 return $this->incr( $key, - $value );
 815         }
 816
 817         /**
 818          * Increase stored value of $key by $value while preserving its TTL
 819          *
 820          * This will create the key with value $init and TTL $ttl instead if not present
 821          *
 822          * @param string $key
 823          * @param int $ttl
 824          * @param int $value
 825          * @param int $init
 826          * @return int|bool New value or false on failure
 827          * @since 1.24
 828          */
 829         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 830                 $this->clearLastError();
 831                 $newValue = $this->incr( $key, $value );
 832                 if ( $newValue === false && !$this->getLastError() ) {
 833                         // No key set; initialize
 834                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 835                         if ( $newValue === false && !$this->getLastError() ) {
 836                                 // Raced out initializing; increment
 837                                 $newValue = $this->incr( $key, $value );
 838                         }
 839                 }
 840
 841                 return $newValue;
 842         }
 843
 844         /**
 845          * Get and reassemble the chunks of blob at the given key
 846          *
 847          * @param string $key
 848          * @param mixed $mainValue
 849          * @return string|null|bool The combined string, false if missing, null on error
 850          */
 851         final protected function resolveSegments( $key, $mainValue ) {
 852                 if ( SerializedValueContainer::isUnified( $mainValue ) ) {
 853                         return $this->unserialize( $mainValue->{SerializedValueContainer::UNIFIED_DATA} );
 854                 }
 855
 856                 if ( SerializedValueContainer::isSegmented( $mainValue ) ) {
 857                         $orderedKeys = array_map(
 858                                 function ( $segmentHash ) use ( $key ) {
 859                                         return $this->makeGlobalKey( self::SEGMENT_COMPONENT, $key, $segmentHash );
 860                                 },
 861                                 $mainValue->{SerializedValueContainer::SEGMENTED_HASHES}
 862                         );
 863
 864                         $segmentsByKey = $this->doGetMulti( $orderedKeys );
 865
 866                         $parts = [];
 867                         foreach ( $orderedKeys as $segmentKey ) {
 868                                 if ( isset( $segmentsByKey[$segmentKey] ) ) {
 869                                         $parts[] = $segmentsByKey[$segmentKey];
 870                                 } else {
 871                                         return false; // missing segment
 872                                 }
 873                         }
 874
 875                         return $this->unserialize( implode( '', $parts ) );
 876                 }
 877
 878                 return $mainValue;
 879         }
 880
 881         /**
 882          * Get the "last error" registered; clearLastError() should be called manually
 883          * @return int ERR_* constant for the "last error" registry
 884          * @since 1.23
 885          */
 886         public function getLastError() {
 887                 return $this->lastError;
 888         }
 889
 890         /**
 891          * Clear the "last error" registry
 892          * @since 1.23
 893          */
 894         public function clearLastError() {
 895                 $this->lastError = self::ERR_NONE;
 896         }
 897
 898         /**
 899          * Set the "last error" registry
 900          * @param int $err ERR_* constant
 901          * @since 1.23
 902          */
 903         protected function setLastError( $err ) {
 904                 $this->lastError = $err;
 905         }
 906
 907         /**
 908          * Let a callback be run to avoid wasting time on special blocking calls
 909          *
 910          * The callbacks may or may not be called ever, in any particular order.
 911          * They are likely to be invoked when something WRITE_SYNC is used used.
 912          * They should follow a caching pattern as shown below, so that any code
 913          * using the work will get it's result no matter what happens.
 914          * @code
 915          *     $result = null;
 916          *     $workCallback = function () use ( &$result ) {
 917          *         if ( !$result ) {
 918          *             $result = ....
 919          *         }
 920          *         return $result;
 921          *     }
 922          * @endcode
 923          *
 924          * @param callable $workCallback
 925          * @since 1.28
 926          */
 927         final public function addBusyCallback( callable $workCallback ) {
 928                 $this->busyCallbacks[] = $workCallback;
 929         }
 930
 931         /**
 932          * @param string $text
 933          */
 934         protected function debug( $text ) {
 935                 if ( $this->debugMode ) {
 936                         $this->logger->debug( "{class} debug: $text", [ 'class' => static::class ] );
 937                 }
 938         }
 939
 940         /**
 941          * @param int $exptime
 942          * @return bool
 943          */
 944         final protected function expiryIsRelative( $exptime ) {
 945                 return ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) );
 946         }
 947
 948         /**
 949          * Convert an optionally relative timestamp to an absolute time
 950          *
 951          * The input value will be cast to an integer and interpreted as follows:
 952          *   - zero: no expiry; return zero (e.g. TTL_INDEFINITE)
 953          *   - negative: relative TTL; return UNIX timestamp offset by this value
 954          *   - positive (< 10 years): relative TTL; return UNIX timestamp offset by this value
 955          *   - positive (>= 10 years): absolute UNIX timestamp; return this value
 956          *
 957          * @param int $exptime Absolute TTL or 0 for indefinite
 958          * @return int
 959          */
 960         final protected function convertToExpiry( $exptime ) {
 961                 return $this->expiryIsRelative( $exptime )
 962                         ? (int)$this->getCurrentTime() + $exptime
 963                         : $exptime;
 964         }
 965
 966         /**
 967          * Convert an optionally absolute expiry time to a relative time. If an
 968          * absolute time is specified which is in the past, use a short expiry time.
 969          *
 970          * @param int $exptime
 971          * @return int
 972          */
 973         final protected function convertToRelative( $exptime ) {
 974                 return $this->expiryIsRelative( $exptime )
 975                         ? (int)$exptime
 976                         : max( $exptime - (int)$this->getCurrentTime(), 1 );
 977         }
 978
 979         /**
 980          * Check if a value is an integer
 981          *
 982          * @param mixed $value
 983          * @return bool
 984          */
 985         final protected function isInteger( $value ) {
 986                 if ( is_int( $value ) ) {
 987                         return true;
 988                 } elseif ( !is_string( $value ) ) {
 989                         return false;
 990                 }
 991
 992                 $integer = (int)$value;
 993
 994                 return ( $value === (string)$integer );
 995         }
 996
 997         /**
 998          * Construct a cache key.
 999          *
1000          * @since 1.27
1001          * @param string $keyspace
1002          * @param array $args
1003          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1004          */
1005         public function makeKeyInternal( $keyspace, $args ) {
1006                 $key = $keyspace;
1007                 foreach ( $args as $arg ) {
1008                         $key .= ':' . str_replace( ':', '%3A', $arg );
1009                 }
1010                 return strtr( $key, ' ', '_' );
1011         }
1012
1013         /**
1014          * Make a global cache key.
1015          *
1016          * @since 1.27
1017          * @param string $class Key class
1018          * @param string|null $component [optional] Key component (starting with a key collection name)
1019          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1020          */
1021         public function makeGlobalKey( $class, $component = null ) {
1022                 return $this->makeKeyInternal( 'global', func_get_args() );
1023         }
1024
1025         /**
1026          * Make a cache key, scoped to this instance's keyspace.
1027          *
1028          * @since 1.27
1029          * @param string $class Key class
1030          * @param string|null $component [optional] Key component (starting with a key collection name)
1031          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
1032          */
1033         public function makeKey( $class, $component = null ) {
1034                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
1035         }
1036
1037         /**
1038          * @param int $flag ATTR_* class constant
1039          * @return int QOS_* class constant
1040          * @since 1.28
1041          */
1042         public function getQoS( $flag ) {
1043                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
1044         }
1045
1046         /**
1047          * @return int|float The chunk size, in bytes, of segmented objects (INF for no limit)
1048          * @since 1.34
1049          */
1050         public function getSegmentationSize() {
1051                 return $this->segmentationSize;
1052         }
1053
1054         /**
1055          * @return int|float Maximum total segmented object size in bytes (INF for no limit)
1056          * @since 1.34
1057          */
1058         public function getSegmentedValueMaxSize() {
1059                 return $this->segmentedValueMaxSize;
1060         }
1061
1062         /**
1063          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
1064          *
1065          * @param BagOStuff[] $bags
1066          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
1067          */
1068         final protected function mergeFlagMaps( array $bags ) {
1069                 $map = [];
1070                 foreach ( $bags as $bag ) {
1071                         foreach ( $bag->attrMap as $attr => $rank ) {
1072                                 if ( isset( $map[$attr] ) ) {
1073                                         $map[$attr] = min( $map[$attr], $rank );
1074                                 } else {
1075                                         $map[$attr] = $rank;
1076                                 }
1077                         }
1078                 }
1079
1080                 return $map;
1081         }
1082
1083         /**
1084          * @internal For testing only
1085          * @return float UNIX timestamp
1086          * @codeCoverageIgnore
1087          */
1088         public function getCurrentTime() {
1089                 return $this->wallClockOverride ?: microtime( true );
1090         }
1091
1092         /**
1093          * @internal For testing only
1094          * @param float|null &$time Mock UNIX timestamp
1095          * @codeCoverageIgnore
1096          */
1097         public function setMockTime( &$time ) {
1098                 $this->wallClockOverride =& $time;
1099         }
1100
1101         /**
1102          * @param mixed $value
1103          * @return string|int String/integer representation
1104          * @note Special handling is usually needed for integers so incr()/decr() work
1105          */
1106         protected function serialize( $value ) {
1107                 return is_int( $value ) ? $value : serialize( $value );
1108         }
1109
1110         /**
1111          * @param string|int $value
1112          * @return mixed Original value or false on error
1113          * @note Special handling is usually needed for integers so incr()/decr() work
1114          */
1115         protected function unserialize( $value ) {
1116                 return $this->isInteger( $value ) ? (int)$value : unserialize( $value );
1117         }
1118 }