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  * interface is intended to be more or less compatible with
  37  * the PHP memcached client.
  38  *
  39  * backends for local hash array and SQL table included:
  40  * @code
  41  *   $bag = new HashBagOStuff();
  42  *   $bag = new SqlBagOStuff(); # connect to db first
  43  * @endcode
  44  *
  45  * @ingroup Cache
  46  */
  47 abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
  48         /** @var array[] Lock tracking */
  49         protected $locks = [];
  50         /** @var int ERR_* class constant */
  51         protected $lastError = self::ERR_NONE;
  52         /** @var string */
  53         protected $keyspace = 'local';
  54         /** @var LoggerInterface */
  55         protected $logger;
  56         /** @var callback|null */
  57         protected $asyncHandler;
  58         /** @var int Seconds */
  59         protected $syncTimeout;
  60
  61         /** @var bool */
  62         private $debugMode = false;
  63         /** @var array */
  64         private $duplicateKeyLookups = [];
  65         /** @var bool */
  66         private $reportDupes = false;
  67         /** @var bool */
  68         private $dupeTrackScheduled = false;
  69
  70         /** @var callable[] */
  71         protected $busyCallbacks = [];
  72
  73         /** @var int[] Map of (ATTR_* class constant => QOS_* class constant) */
  74         protected $attrMap = [];
  75
  76         /** Possible values for getLastError() */
  77         const ERR_NONE = 0; // no error
  78         const ERR_NO_RESPONSE = 1; // no response
  79         const ERR_UNREACHABLE = 2; // can't connect
  80         const ERR_UNEXPECTED = 3; // response gave some error
  81
  82         /** Bitfield constants for get()/getMulti() */
  83         const READ_LATEST = 1; // use latest data for replicated stores
  84         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  85         /** Bitfield constants for set()/merge() */
  86         const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
  87         const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache
  88
  89         /**
  90          * $params include:
  91          *   - logger: Psr\Log\LoggerInterface instance
  92          *   - keyspace: Default keyspace for $this->makeKey()
  93          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
  94          *      In CLI mode, it should run the task immediately.
  95          *   - reportDupes: Whether to emit warning log messages for all keys that were
  96          *      requested more than once (requires an asyncHandler).
  97          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
  98          * @param array $params
  99          */
 100         public function __construct( array $params = [] ) {
 101                 if ( isset( $params['logger'] ) ) {
 102                         $this->setLogger( $params['logger'] );
 103                 } else {
 104                         $this->setLogger( new NullLogger() );
 105                 }
 106
 107                 if ( isset( $params['keyspace'] ) ) {
 108                         $this->keyspace = $params['keyspace'];
 109                 }
 110
 111                 $this->asyncHandler = isset( $params['asyncHandler'] )
 112                         ? $params['asyncHandler']
 113                         : null;
 114
 115                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 116                         $this->reportDupes = true;
 117                 }
 118
 119                 $this->syncTimeout = isset( $params['syncTimeout'] ) ? $params['syncTimeout'] : 3;
 120         }
 121
 122         /**
 123          * @param LoggerInterface $logger
 124          * @return null
 125          */
 126         public function setLogger( LoggerInterface $logger ) {
 127                 $this->logger = $logger;
 128         }
 129
 130         /**
 131          * @param bool $bool
 132          */
 133         public function setDebug( $bool ) {
 134                 $this->debugMode = $bool;
 135         }
 136
 137         /**
 138          * Get an item with the given key, regenerating and setting it if not found
 139          *
 140          * If the callback returns false, then nothing is stored.
 141          *
 142          * @param string $key
 143          * @param int $ttl Time-to-live (seconds)
 144          * @param callable $callback Callback that derives the new value
 145          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 146          * @return mixed The cached value if found or the result of $callback otherwise
 147          * @since 1.27
 148          */
 149         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 150                 $value = $this->get( $key, $flags );
 151
 152                 if ( $value === false ) {
 153                         if ( !is_callable( $callback ) ) {
 154                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 155                         }
 156                         $value = call_user_func( $callback );
 157                         if ( $value !== false ) {
 158                                 $this->set( $key, $value, $ttl );
 159                         }
 160                 }
 161
 162                 return $value;
 163         }
 164
 165         /**
 166          * Get an item with the given key
 167          *
 168          * If the key includes a determistic input hash (e.g. the key can only have
 169          * the correct value) or complete staleness checks are handled by the caller
 170          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 171          * This lets tiered backends know they can safely upgrade a cached value to
 172          * higher tiers using standard TTLs.
 173          *
 174          * @param string $key
 175          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 176          * @param int $oldFlags [unused]
 177          * @return mixed Returns false on failure and if the item does not exist
 178          */
 179         public function get( $key, $flags = 0, $oldFlags = null ) {
 180                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 181                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 182
 183                 $this->trackDuplicateKeys( $key );
 184
 185                 return $this->doGet( $key, $flags );
 186         }
 187
 188         /**
 189          * Track the number of times that a given key has been used.
 190          * @param string $key
 191          */
 192         private function trackDuplicateKeys( $key ) {
 193                 if ( !$this->reportDupes ) {
 194                         return;
 195                 }
 196
 197                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 198                         // Track that we have seen this key. This N-1 counting style allows
 199                         // easy filtering with array_filter() later.
 200                         $this->duplicateKeyLookups[$key] = 0;
 201                 } else {
 202                         $this->duplicateKeyLookups[$key] += 1;
 203
 204                         if ( $this->dupeTrackScheduled === false ) {
 205                                 $this->dupeTrackScheduled = true;
 206                                 // Schedule a callback that logs keys processed more than once by get().
 207                                 call_user_func( $this->asyncHandler, function () {
 208                                         $dups = array_filter( $this->duplicateKeyLookups );
 209                                         foreach ( $dups as $key => $count ) {
 210                                                 $this->logger->warning(
 211                                                         'Duplicate get(): "{key}" fetched {count} times',
 212                                                         // Count is N-1 of the actual lookup count
 213                                                         [ 'key' => $key, 'count' => $count + 1, ]
 214                                                 );
 215                                         }
 216                                 } );
 217                         }
 218                 }
 219         }
 220
 221         /**
 222          * @param string $key
 223          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 224          * @return mixed Returns false on failure and if the item does not exist
 225          */
 226         abstract protected function doGet( $key, $flags = 0 );
 227
 228         /**
 229          * @note: This method is only needed if merge() uses mergeViaCas()
 230          *
 231          * @param string $key
 232          * @param mixed &$casToken
 233          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 234          * @return mixed Returns false on failure and if the item does not exist
 235          * @throws Exception
 236          */
 237         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 238                 throw new Exception( __METHOD__ . ' not implemented.' );
 239         }
 240
 241         /**
 242          * Set an item
 243          *
 244          * @param string $key
 245          * @param mixed $value
 246          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 247          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 248          * @return bool Success
 249          */
 250         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 251
 252         /**
 253          * Delete an item
 254          *
 255          * @param string $key
 256          * @return bool True if the item was deleted or not found, false on failure
 257          */
 258         abstract public function delete( $key );
 259
 260         /**
 261          * Merge changes into the existing cache value (possibly creating a new one)
 262          *
 263          * The callback function returns the new value given the current value
 264          * (which will be false if not present), and takes the arguments:
 265          * (this BagOStuff, cache key, current value, TTL).
 266          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 267          *
 268          * @param string $key
 269          * @param callable $callback Callback method to be executed
 270          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 271          * @param int $attempts The amount of times to attempt a merge in case of failure
 272          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 273          * @return bool Success
 274          * @throws InvalidArgumentException
 275          */
 276         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 277                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 278         }
 279
 280         /**
 281          * @see BagOStuff::merge()
 282          *
 283          * @param string $key
 284          * @param callable $callback Callback method to be executed
 285          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 286          * @param int $attempts The amount of times to attempt a merge in case of failure
 287          * @return bool Success
 288          */
 289         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 290                 do {
 291                         $this->clearLastError();
 292                         $reportDupes = $this->reportDupes;
 293                         $this->reportDupes = false;
 294                         $casToken = null; // passed by reference
 295                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 296                         $this->reportDupes = $reportDupes;
 297
 298                         if ( $this->getLastError() ) {
 299                                 return false; // don't spam retries (retry only on races)
 300                         }
 301
 302                         // Derive the new value from the old value
 303                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 304
 305                         $this->clearLastError();
 306                         if ( $value === false ) {
 307                                 $success = true; // do nothing
 308                         } elseif ( $currentValue === false ) {
 309                                 // Try to create the key, failing if it gets created in the meantime
 310                                 $success = $this->add( $key, $value, $exptime );
 311                         } else {
 312                                 // Try to update the key, failing if it gets changed in the meantime
 313                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 314                         }
 315                         if ( $this->getLastError() ) {
 316                                 return false; // IO error; don't spam retries
 317                         }
 318                 } while ( !$success && --$attempts );
 319
 320                 return $success;
 321         }
 322
 323         /**
 324          * Check and set an item
 325          *
 326          * @param mixed $casToken
 327          * @param string $key
 328          * @param mixed $value
 329          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 330          * @return bool Success
 331          * @throws Exception
 332          */
 333         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 334                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 335         }
 336
 337         /**
 338          * @see BagOStuff::merge()
 339          *
 340          * @param string $key
 341          * @param callable $callback Callback method to be executed
 342          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 343          * @param int $attempts The amount of times to attempt a merge in case of failure
 344          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 345          * @return bool Success
 346          */
 347         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 348                 if ( !$this->lock( $key, 6 ) ) {
 349                         return false;
 350                 }
 351
 352                 $this->clearLastError();
 353                 $reportDupes = $this->reportDupes;
 354                 $this->reportDupes = false;
 355                 $currentValue = $this->get( $key, self::READ_LATEST );
 356                 $this->reportDupes = $reportDupes;
 357
 358                 if ( $this->getLastError() ) {
 359                         $success = false;
 360                 } else {
 361                         // Derive the new value from the old value
 362                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 363                         if ( $value === false ) {
 364                                 $success = true; // do nothing
 365                         } else {
 366                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 367                         }
 368                 }
 369
 370                 if ( !$this->unlock( $key ) ) {
 371                         // this should never happen
 372                         trigger_error( "Could not release lock for key '$key'." );
 373                 }
 374
 375                 return $success;
 376         }
 377
 378         /**
 379          * Reset the TTL on a key if it exists
 380          *
 381          * @param string $key
 382          * @param int $expiry
 383          * @return bool Success Returns false if there is no key
 384          * @since 1.28
 385          */
 386         public function changeTTL( $key, $expiry = 0 ) {
 387                 $value = $this->get( $key );
 388
 389                 return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
 390         }
 391
 392         /**
 393          * Acquire an advisory lock on a key string
 394          *
 395          * Note that if reentry is enabled, duplicate calls ignore $expiry
 396          *
 397          * @param string $key
 398          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 399          * @param int $expiry Lock expiry [optional]; 1 day maximum
 400          * @param string $rclass Allow reentry if set and the current lock used this value
 401          * @return bool Success
 402          */
 403         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 404                 // Avoid deadlocks and allow lock reentry if specified
 405                 if ( isset( $this->locks[$key] ) ) {
 406                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 407                                 ++$this->locks[$key]['depth'];
 408                                 return true;
 409                         } else {
 410                                 return false;
 411                         }
 412                 }
 413
 414                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 415                 $loop = new WaitConditionLoop(
 416                         function () use ( $key, $timeout, $expiry ) {
 417                                 $this->clearLastError();
 418                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 419                                         return true; // locked!
 420                                 } elseif ( $this->getLastError() ) {
 421                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 422                                 }
 423
 424                                 return WaitConditionLoop::CONDITION_CONTINUE;
 425                         },
 426                         $timeout
 427                 );
 428
 429                 $locked = ( $loop->invoke() === $loop::CONDITION_REACHED );
 430                 if ( $locked ) {
 431                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 432                 }
 433
 434                 return $locked;
 435         }
 436
 437         /**
 438          * Release an advisory lock on a key string
 439          *
 440          * @param string $key
 441          * @return bool Success
 442          */
 443         public function unlock( $key ) {
 444                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 445                         unset( $this->locks[$key] );
 446
 447                         return $this->delete( "{$key}:lock" );
 448                 }
 449
 450                 return true;
 451         }
 452
 453         /**
 454          * Get a lightweight exclusive self-unlocking lock
 455          *
 456          * Note that the same lock cannot be acquired twice.
 457          *
 458          * This is useful for task de-duplication or to avoid obtrusive
 459          * (though non-corrupting) DB errors like INSERT key conflicts
 460          * or deadlocks when using LOCK IN SHARE MODE.
 461          *
 462          * @param string $key
 463          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 464          * @param int $expiry Lock expiry [optional]; 1 day maximum
 465          * @param string $rclass Allow reentry if set and the current lock used this value
 466          * @return ScopedCallback|null Returns null on failure
 467          * @since 1.26
 468          */
 469         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 470                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 471
 472                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 473                         return null;
 474                 }
 475
 476                 $lSince = microtime( true ); // lock timestamp
 477
 478                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 479                         $latency = 0.050; // latency skew (err towards keeping lock present)
 480                         $age = ( microtime( true ) - $lSince + $latency );
 481                         if ( ( $age + $latency ) >= $expiry ) {
 482                                 $this->logger->warning( "Lock for $key held too long ($age sec)." );
 483                                 return; // expired; it's not "safe" to delete the key
 484                         }
 485                         $this->unlock( $key );
 486                 } );
 487         }
 488
 489         /**
 490          * Delete all objects expiring before a certain date.
 491          * @param string $date The reference date in MW format
 492          * @param callable|bool $progressCallback Optional, a function which will be called
 493          *     regularly during long-running operations with the percentage progress
 494          *     as the first parameter.
 495          *
 496          * @return bool Success, false if unimplemented
 497          */
 498         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 499                 // stub
 500                 return false;
 501         }
 502
 503         /**
 504          * Get an associative array containing the item for each of the keys that have items.
 505          * @param array $keys List of strings
 506          * @param int $flags Bitfield; supports READ_LATEST [optional]
 507          * @return array
 508          */
 509         public function getMulti( array $keys, $flags = 0 ) {
 510                 $res = [];
 511                 foreach ( $keys as $key ) {
 512                         $val = $this->get( $key );
 513                         if ( $val !== false ) {
 514                                 $res[$key] = $val;
 515                         }
 516                 }
 517                 return $res;
 518         }
 519
 520         /**
 521          * Batch insertion
 522          * @param array $data $key => $value assoc array
 523          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 524          * @return bool Success
 525          * @since 1.24
 526          */
 527         public function setMulti( array $data, $exptime = 0 ) {
 528                 $res = true;
 529                 foreach ( $data as $key => $value ) {
 530                         if ( !$this->set( $key, $value, $exptime ) ) {
 531                                 $res = false;
 532                         }
 533                 }
 534                 return $res;
 535         }
 536
 537         /**
 538          * @param string $key
 539          * @param mixed $value
 540          * @param int $exptime
 541          * @return bool Success
 542          */
 543         public function add( $key, $value, $exptime = 0 ) {
 544                 if ( $this->get( $key ) === false ) {
 545                         return $this->set( $key, $value, $exptime );
 546                 }
 547                 return false; // key already set
 548         }
 549
 550         /**
 551          * Increase stored value of $key by $value while preserving its TTL
 552          * @param string $key Key to increase
 553          * @param int $value Value to add to $key (Default 1)
 554          * @return int|bool New value or false on failure
 555          */
 556         public function incr( $key, $value = 1 ) {
 557                 if ( !$this->lock( $key ) ) {
 558                         return false;
 559                 }
 560                 $n = $this->get( $key );
 561                 if ( $this->isInteger( $n ) ) { // key exists?
 562                         $n += intval( $value );
 563                         $this->set( $key, max( 0, $n ) ); // exptime?
 564                 } else {
 565                         $n = false;
 566                 }
 567                 $this->unlock( $key );
 568
 569                 return $n;
 570         }
 571
 572         /**
 573          * Decrease stored value of $key by $value while preserving its TTL
 574          * @param string $key
 575          * @param int $value
 576          * @return int|bool New value or false on failure
 577          */
 578         public function decr( $key, $value = 1 ) {
 579                 return $this->incr( $key, - $value );
 580         }
 581
 582         /**
 583          * Increase stored value of $key by $value while preserving its TTL
 584          *
 585          * This will create the key with value $init and TTL $ttl instead if not present
 586          *
 587          * @param string $key
 588          * @param int $ttl
 589          * @param int $value
 590          * @param int $init
 591          * @return int|bool New value or false on failure
 592          * @since 1.24
 593          */
 594         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 595                 $newValue = $this->incr( $key, $value );
 596                 if ( $newValue === false ) {
 597                         // No key set; initialize
 598                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 599                 }
 600                 if ( $newValue === false ) {
 601                         // Raced out initializing; increment
 602                         $newValue = $this->incr( $key, $value );
 603                 }
 604
 605                 return $newValue;
 606         }
 607
 608         /**
 609          * Get the "last error" registered; clearLastError() should be called manually
 610          * @return int ERR_* constant for the "last error" registry
 611          * @since 1.23
 612          */
 613         public function getLastError() {
 614                 return $this->lastError;
 615         }
 616
 617         /**
 618          * Clear the "last error" registry
 619          * @since 1.23
 620          */
 621         public function clearLastError() {
 622                 $this->lastError = self::ERR_NONE;
 623         }
 624
 625         /**
 626          * Set the "last error" registry
 627          * @param int $err ERR_* constant
 628          * @since 1.23
 629          */
 630         protected function setLastError( $err ) {
 631                 $this->lastError = $err;
 632         }
 633
 634         /**
 635          * Let a callback be run to avoid wasting time on special blocking calls
 636          *
 637          * The callbacks may or may not be called ever, in any particular order.
 638          * They are likely to be invoked when something WRITE_SYNC is used used.
 639          * They should follow a caching pattern as shown below, so that any code
 640          * using the word will get it's result no matter what happens.
 641          * @code
 642          *     $result = null;
 643          *     $workCallback = function () use ( &$result ) {
 644          *         if ( !$result ) {
 645          *             $result = ....
 646          *         }
 647          *         return $result;
 648          *     }
 649          * @endcode
 650          *
 651          * @param callable $workCallback
 652          * @since 1.28
 653          */
 654         public function addBusyCallback( callable $workCallback ) {
 655                 $this->busyCallbacks[] = $workCallback;
 656         }
 657
 658         /**
 659          * Modify a cache update operation array for EventRelayer::notify()
 660          *
 661          * This is used for relayed writes, e.g. for broadcasting a change
 662          * to multiple data-centers. If the array contains a 'val' field
 663          * then the command involves setting a key to that value. Note that
 664          * for simplicity, 'val' is always a simple scalar value. This method
 665          * is used to possibly serialize the value and add any cache-specific
 666          * key/values needed for the relayer daemon (e.g. memcached flags).
 667          *
 668          * @param array $event
 669          * @return array
 670          * @since 1.26
 671          */
 672         public function modifySimpleRelayEvent( array $event ) {
 673                 return $event;
 674         }
 675
 676         /**
 677          * @param string $text
 678          */
 679         protected function debug( $text ) {
 680                 if ( $this->debugMode ) {
 681                         $this->logger->debug( "{class} debug: $text", [
 682                                 'class' => static::class,
 683                         ] );
 684                 }
 685         }
 686
 687         /**
 688          * Convert an optionally relative time to an absolute time
 689          * @param int $exptime
 690          * @return int
 691          */
 692         protected function convertExpiry( $exptime ) {
 693                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 694                         return time() + $exptime;
 695                 } else {
 696                         return $exptime;
 697                 }
 698         }
 699
 700         /**
 701          * Convert an optionally absolute expiry time to a relative time. If an
 702          * absolute time is specified which is in the past, use a short expiry time.
 703          *
 704          * @param int $exptime
 705          * @return int
 706          */
 707         protected function convertToRelative( $exptime ) {
 708                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 709                         $exptime -= time();
 710                         if ( $exptime <= 0 ) {
 711                                 $exptime = 1;
 712                         }
 713                         return $exptime;
 714                 } else {
 715                         return $exptime;
 716                 }
 717         }
 718
 719         /**
 720          * Check if a value is an integer
 721          *
 722          * @param mixed $value
 723          * @return bool
 724          */
 725         protected function isInteger( $value ) {
 726                 return ( is_int( $value ) || ctype_digit( $value ) );
 727         }
 728
 729         /**
 730          * Construct a cache key.
 731          *
 732          * @since 1.27
 733          * @param string $keyspace
 734          * @param array $args
 735          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 736          */
 737         public function makeKeyInternal( $keyspace, $args ) {
 738                 $key = $keyspace;
 739                 foreach ( $args as $arg ) {
 740                         $arg = str_replace( ':', '%3A', $arg );
 741                         $key = $key . ':' . $arg;
 742                 }
 743                 return strtr( $key, ' ', '_' );
 744         }
 745
 746         /**
 747          * Make a global cache key.
 748          *
 749          * @since 1.27
 750          * @param string $class Key class
 751          * @param string $component [optional] Key component (starting with a key collection name)
 752          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 753          */
 754         public function makeGlobalKey( $class, $component = null ) {
 755                 return $this->makeKeyInternal( 'global', func_get_args() );
 756         }
 757
 758         /**
 759          * Make a cache key, scoped to this instance's keyspace.
 760          *
 761          * @since 1.27
 762          * @param string $class Key class
 763          * @param string $component [optional] Key component (starting with a key collection name)
 764          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 765          */
 766         public function makeKey( $class, $component = null ) {
 767                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 768         }
 769
 770         /**
 771          * @param int $flag ATTR_* class constant
 772          * @return int QOS_* class constant
 773          * @since 1.28
 774          */
 775         public function getQoS( $flag ) {
 776                 return isset( $this->attrMap[$flag] ) ? $this->attrMap[$flag] : self::QOS_UNKNOWN;
 777         }
 778
 779         /**
 780          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 781          *
 782          * @param BagOStuff[] $bags
 783          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 784          */
 785         protected function mergeFlagMaps( array $bags ) {
 786                 $map = [];
 787                 foreach ( $bags as $bag ) {
 788                         foreach ( $bag->attrMap as $attr => $rank ) {
 789                                 if ( isset( $map[$attr] ) ) {
 790                                         $map[$attr] = min( $map[$attr], $rank );
 791                                 } else {
 792                                         $map[$attr] = $rank;
 793                                 }
 794                         }
 795                 }
 796
 797                 return $map;
 798         }
 799 }