includes/libs/objectcache/MediumSpecificBagOStuff.php

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