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 access
  54  * scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
  55  *
  56  * @ingroup Cache
  57  */
  58 abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
  59         /** @var array[] Lock tracking */
  60         protected $locks = [];
  61         /** @var int ERR_* class constant */
  62         protected $lastError = self::ERR_NONE;
  63         /** @var string */
  64         protected $keyspace = 'local';
  65         /** @var LoggerInterface */
  66         protected $logger;
  67         /** @var callback|null */
  68         protected $asyncHandler;
  69         /** @var int Seconds */
  70         protected $syncTimeout;
  71
  72         /** @var bool */
  73         private $debugMode = false;
  74         /** @var array */
  75         private $duplicateKeyLookups = [];
  76         /** @var bool */
  77         private $reportDupes = false;
  78         /** @var bool */
  79         private $dupeTrackScheduled = false;
  80
  81         /** @var callable[] */
  82         protected $busyCallbacks = [];
  83
  84         /** @var int[] Map of (ATTR_* class constant => QOS_* class constant) */
  85         protected $attrMap = [];
  86
  87         /** Possible values for getLastError() */
  88         const ERR_NONE = 0; // no error
  89         const ERR_NO_RESPONSE = 1; // no response
  90         const ERR_UNREACHABLE = 2; // can't connect
  91         const ERR_UNEXPECTED = 3; // response gave some error
  92
  93         /** Bitfield constants for get()/getMulti() */
  94         const READ_LATEST = 1; // use latest data for replicated stores
  95         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  96         /** Bitfield constants for set()/merge() */
  97         const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
  98         const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache
  99
 100         /**
 101          * $params include:
 102          *   - logger: Psr\Log\LoggerInterface instance
 103          *   - keyspace: Default keyspace for $this->makeKey()
 104          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
 105          *      In CLI mode, it should run the task immediately.
 106          *   - reportDupes: Whether to emit warning log messages for all keys that were
 107          *      requested more than once (requires an asyncHandler).
 108          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
 109          * @param array $params
 110          */
 111         public function __construct( array $params = [] ) {
 112                 if ( isset( $params['logger'] ) ) {
 113                         $this->setLogger( $params['logger'] );
 114                 } else {
 115                         $this->setLogger( new NullLogger() );
 116                 }
 117
 118                 if ( isset( $params['keyspace'] ) ) {
 119                         $this->keyspace = $params['keyspace'];
 120                 }
 121
 122                 $this->asyncHandler = isset( $params['asyncHandler'] )
 123                         ? $params['asyncHandler']
 124                         : null;
 125
 126                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 127                         $this->reportDupes = true;
 128                 }
 129
 130                 $this->syncTimeout = isset( $params['syncTimeout'] ) ? $params['syncTimeout'] : 3;
 131         }
 132
 133         /**
 134          * @param LoggerInterface $logger
 135          * @return null
 136          */
 137         public function setLogger( LoggerInterface $logger ) {
 138                 $this->logger = $logger;
 139         }
 140
 141         /**
 142          * @param bool $bool
 143          */
 144         public function setDebug( $bool ) {
 145                 $this->debugMode = $bool;
 146         }
 147
 148         /**
 149          * Get an item with the given key, regenerating and setting it if not found
 150          *
 151          * If the callback returns false, then nothing is stored.
 152          *
 153          * @param string $key
 154          * @param int $ttl Time-to-live (seconds)
 155          * @param callable $callback Callback that derives the new value
 156          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 157          * @return mixed The cached value if found or the result of $callback otherwise
 158          * @since 1.27
 159          */
 160         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 161                 $value = $this->get( $key, $flags );
 162
 163                 if ( $value === false ) {
 164                         if ( !is_callable( $callback ) ) {
 165                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 166                         }
 167                         $value = call_user_func( $callback );
 168                         if ( $value !== false ) {
 169                                 $this->set( $key, $value, $ttl );
 170                         }
 171                 }
 172
 173                 return $value;
 174         }
 175
 176         /**
 177          * Get an item with the given key
 178          *
 179          * If the key includes a deterministic input hash (e.g. the key can only have
 180          * the correct value) or complete staleness checks are handled by the caller
 181          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 182          * This lets tiered backends know they can safely upgrade a cached value to
 183          * higher tiers using standard TTLs.
 184          *
 185          * @param string $key
 186          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 187          * @param int $oldFlags [unused]
 188          * @return mixed Returns false on failure and if the item does not exist
 189          */
 190         public function get( $key, $flags = 0, $oldFlags = null ) {
 191                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 192                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 193
 194                 $this->trackDuplicateKeys( $key );
 195
 196                 return $this->doGet( $key, $flags );
 197         }
 198
 199         /**
 200          * Track the number of times that a given key has been used.
 201          * @param string $key
 202          */
 203         private function trackDuplicateKeys( $key ) {
 204                 if ( !$this->reportDupes ) {
 205                         return;
 206                 }
 207
 208                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 209                         // Track that we have seen this key. This N-1 counting style allows
 210                         // easy filtering with array_filter() later.
 211                         $this->duplicateKeyLookups[$key] = 0;
 212                 } else {
 213                         $this->duplicateKeyLookups[$key] += 1;
 214
 215                         if ( $this->dupeTrackScheduled === false ) {
 216                                 $this->dupeTrackScheduled = true;
 217                                 // Schedule a callback that logs keys processed more than once by get().
 218                                 call_user_func( $this->asyncHandler, function () {
 219                                         $dups = array_filter( $this->duplicateKeyLookups );
 220                                         foreach ( $dups as $key => $count ) {
 221                                                 $this->logger->warning(
 222                                                         'Duplicate get(): "{key}" fetched {count} times',
 223                                                         // Count is N-1 of the actual lookup count
 224                                                         [ 'key' => $key, 'count' => $count + 1, ]
 225                                                 );
 226                                         }
 227                                 } );
 228                         }
 229                 }
 230         }
 231
 232         /**
 233          * @param string $key
 234          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 235          * @return mixed Returns false on failure and if the item does not exist
 236          */
 237         abstract protected function doGet( $key, $flags = 0 );
 238
 239         /**
 240          * @note: This method is only needed if merge() uses mergeViaCas()
 241          *
 242          * @param string $key
 243          * @param mixed &$casToken
 244          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 245          * @return mixed Returns false on failure and if the item does not exist
 246          * @throws Exception
 247          */
 248         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 249                 throw new Exception( __METHOD__ . ' not implemented.' );
 250         }
 251
 252         /**
 253          * Set an item
 254          *
 255          * @param string $key
 256          * @param mixed $value
 257          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 258          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 259          * @return bool Success
 260          */
 261         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 262
 263         /**
 264          * Delete an item
 265          *
 266          * @param string $key
 267          * @return bool True if the item was deleted or not found, false on failure
 268          */
 269         abstract public function delete( $key );
 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          *
 279          * @param string $key
 280          * @param callable $callback Callback method to be executed
 281          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 282          * @param int $attempts The amount of times to attempt a merge in case of failure
 283          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 284          * @return bool Success
 285          * @throws InvalidArgumentException
 286          */
 287         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 288                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 289         }
 290
 291         /**
 292          * @see BagOStuff::merge()
 293          *
 294          * @param string $key
 295          * @param callable $callback Callback method to be executed
 296          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 297          * @param int $attempts The amount of times to attempt a merge in case of failure
 298          * @return bool Success
 299          */
 300         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 301                 do {
 302                         $this->clearLastError();
 303                         $reportDupes = $this->reportDupes;
 304                         $this->reportDupes = false;
 305                         $casToken = null; // passed by reference
 306                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 307                         $this->reportDupes = $reportDupes;
 308
 309                         if ( $this->getLastError() ) {
 310                                 return false; // don't spam retries (retry only on races)
 311                         }
 312
 313                         // Derive the new value from the old value
 314                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 315
 316                         $this->clearLastError();
 317                         if ( $value === false ) {
 318                                 $success = true; // do nothing
 319                         } elseif ( $currentValue === false ) {
 320                                 // Try to create the key, failing if it gets created in the meantime
 321                                 $success = $this->add( $key, $value, $exptime );
 322                         } else {
 323                                 // Try to update the key, failing if it gets changed in the meantime
 324                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 325                         }
 326                         if ( $this->getLastError() ) {
 327                                 return false; // IO error; don't spam retries
 328                         }
 329                 } while ( !$success && --$attempts );
 330
 331                 return $success;
 332         }
 333
 334         /**
 335          * Check and set an item
 336          *
 337          * @param mixed $casToken
 338          * @param string $key
 339          * @param mixed $value
 340          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 341          * @return bool Success
 342          * @throws Exception
 343          */
 344         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 345                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 346         }
 347
 348         /**
 349          * @see BagOStuff::merge()
 350          *
 351          * @param string $key
 352          * @param callable $callback Callback method to be executed
 353          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 354          * @param int $attempts The amount of times to attempt a merge in case of failure
 355          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 356          * @return bool Success
 357          */
 358         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 359                 if ( !$this->lock( $key, 6 ) ) {
 360                         return false;
 361                 }
 362
 363                 $this->clearLastError();
 364                 $reportDupes = $this->reportDupes;
 365                 $this->reportDupes = false;
 366                 $currentValue = $this->get( $key, self::READ_LATEST );
 367                 $this->reportDupes = $reportDupes;
 368
 369                 if ( $this->getLastError() ) {
 370                         $success = false;
 371                 } else {
 372                         // Derive the new value from the old value
 373                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 374                         if ( $value === false ) {
 375                                 $success = true; // do nothing
 376                         } else {
 377                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 378                         }
 379                 }
 380
 381                 if ( !$this->unlock( $key ) ) {
 382                         // this should never happen
 383                         trigger_error( "Could not release lock for key '$key'." );
 384                 }
 385
 386                 return $success;
 387         }
 388
 389         /**
 390          * Reset the TTL on a key if it exists
 391          *
 392          * @param string $key
 393          * @param int $expiry
 394          * @return bool Success Returns false if there is no key
 395          * @since 1.28
 396          */
 397         public function changeTTL( $key, $expiry = 0 ) {
 398                 $value = $this->get( $key );
 399
 400                 return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
 401         }
 402
 403         /**
 404          * Acquire an advisory lock on a key string
 405          *
 406          * Note that if reentry is enabled, duplicate calls ignore $expiry
 407          *
 408          * @param string $key
 409          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 410          * @param int $expiry Lock expiry [optional]; 1 day maximum
 411          * @param string $rclass Allow reentry if set and the current lock used this value
 412          * @return bool Success
 413          */
 414         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 415                 // Avoid deadlocks and allow lock reentry if specified
 416                 if ( isset( $this->locks[$key] ) ) {
 417                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 418                                 ++$this->locks[$key]['depth'];
 419                                 return true;
 420                         } else {
 421                                 return false;
 422                         }
 423                 }
 424
 425                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 426                 $loop = new WaitConditionLoop(
 427                         function () use ( $key, $timeout, $expiry ) {
 428                                 $this->clearLastError();
 429                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 430                                         return true; // locked!
 431                                 } elseif ( $this->getLastError() ) {
 432                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 433                                 }
 434
 435                                 return WaitConditionLoop::CONDITION_CONTINUE;
 436                         },
 437                         $timeout
 438                 );
 439
 440                 $locked = ( $loop->invoke() === $loop::CONDITION_REACHED );
 441                 if ( $locked ) {
 442                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 443                 }
 444
 445                 return $locked;
 446         }
 447
 448         /**
 449          * Release an advisory lock on a key string
 450          *
 451          * @param string $key
 452          * @return bool Success
 453          */
 454         public function unlock( $key ) {
 455                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 456                         unset( $this->locks[$key] );
 457
 458                         return $this->delete( "{$key}:lock" );
 459                 }
 460
 461                 return true;
 462         }
 463
 464         /**
 465          * Get a lightweight exclusive self-unlocking lock
 466          *
 467          * Note that the same lock cannot be acquired twice.
 468          *
 469          * This is useful for task de-duplication or to avoid obtrusive
 470          * (though non-corrupting) DB errors like INSERT key conflicts
 471          * or deadlocks when using LOCK IN SHARE MODE.
 472          *
 473          * @param string $key
 474          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 475          * @param int $expiry Lock expiry [optional]; 1 day maximum
 476          * @param string $rclass Allow reentry if set and the current lock used this value
 477          * @return ScopedCallback|null Returns null on failure
 478          * @since 1.26
 479          */
 480         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 481                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 482
 483                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 484                         return null;
 485                 }
 486
 487                 $lSince = microtime( true ); // lock timestamp
 488
 489                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 490                         $latency = 0.050; // latency skew (err towards keeping lock present)
 491                         $age = ( microtime( true ) - $lSince + $latency );
 492                         if ( ( $age + $latency ) >= $expiry ) {
 493                                 $this->logger->warning( "Lock for $key held too long ($age sec)." );
 494                                 return; // expired; it's not "safe" to delete the key
 495                         }
 496                         $this->unlock( $key );
 497                 } );
 498         }
 499
 500         /**
 501          * Delete all objects expiring before a certain date.
 502          * @param string $date The reference date in MW format
 503          * @param callable|bool $progressCallback Optional, a function which will be called
 504          *     regularly during long-running operations with the percentage progress
 505          *     as the first parameter.
 506          *
 507          * @return bool Success, false if unimplemented
 508          */
 509         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 510                 // stub
 511                 return false;
 512         }
 513
 514         /**
 515          * Get an associative array containing the item for each of the keys that have items.
 516          * @param array $keys List of strings
 517          * @param int $flags Bitfield; supports READ_LATEST [optional]
 518          * @return array
 519          */
 520         public function getMulti( array $keys, $flags = 0 ) {
 521                 $res = [];
 522                 foreach ( $keys as $key ) {
 523                         $val = $this->get( $key );
 524                         if ( $val !== false ) {
 525                                 $res[$key] = $val;
 526                         }
 527                 }
 528                 return $res;
 529         }
 530
 531         /**
 532          * Batch insertion
 533          * @param array $data $key => $value assoc array
 534          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 535          * @return bool Success
 536          * @since 1.24
 537          */
 538         public function setMulti( array $data, $exptime = 0 ) {
 539                 $res = true;
 540                 foreach ( $data as $key => $value ) {
 541                         if ( !$this->set( $key, $value, $exptime ) ) {
 542                                 $res = false;
 543                         }
 544                 }
 545                 return $res;
 546         }
 547
 548         /**
 549          * @param string $key
 550          * @param mixed $value
 551          * @param int $exptime
 552          * @return bool Success
 553          */
 554         public function add( $key, $value, $exptime = 0 ) {
 555                 if ( $this->get( $key ) === false ) {
 556                         return $this->set( $key, $value, $exptime );
 557                 }
 558                 return false; // key already set
 559         }
 560
 561         /**
 562          * Increase stored value of $key by $value while preserving its TTL
 563          * @param string $key Key to increase
 564          * @param int $value Value to add to $key (Default 1)
 565          * @return int|bool New value or false on failure
 566          */
 567         public function incr( $key, $value = 1 ) {
 568                 if ( !$this->lock( $key ) ) {
 569                         return false;
 570                 }
 571                 $n = $this->get( $key );
 572                 if ( $this->isInteger( $n ) ) { // key exists?
 573                         $n += intval( $value );
 574                         $this->set( $key, max( 0, $n ) ); // exptime?
 575                 } else {
 576                         $n = false;
 577                 }
 578                 $this->unlock( $key );
 579
 580                 return $n;
 581         }
 582
 583         /**
 584          * Decrease stored value of $key by $value while preserving its TTL
 585          * @param string $key
 586          * @param int $value
 587          * @return int|bool New value or false on failure
 588          */
 589         public function decr( $key, $value = 1 ) {
 590                 return $this->incr( $key, - $value );
 591         }
 592
 593         /**
 594          * Increase stored value of $key by $value while preserving its TTL
 595          *
 596          * This will create the key with value $init and TTL $ttl instead if not present
 597          *
 598          * @param string $key
 599          * @param int $ttl
 600          * @param int $value
 601          * @param int $init
 602          * @return int|bool New value or false on failure
 603          * @since 1.24
 604          */
 605         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 606                 $newValue = $this->incr( $key, $value );
 607                 if ( $newValue === false ) {
 608                         // No key set; initialize
 609                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 610                 }
 611                 if ( $newValue === false ) {
 612                         // Raced out initializing; increment
 613                         $newValue = $this->incr( $key, $value );
 614                 }
 615
 616                 return $newValue;
 617         }
 618
 619         /**
 620          * Get the "last error" registered; clearLastError() should be called manually
 621          * @return int ERR_* constant for the "last error" registry
 622          * @since 1.23
 623          */
 624         public function getLastError() {
 625                 return $this->lastError;
 626         }
 627
 628         /**
 629          * Clear the "last error" registry
 630          * @since 1.23
 631          */
 632         public function clearLastError() {
 633                 $this->lastError = self::ERR_NONE;
 634         }
 635
 636         /**
 637          * Set the "last error" registry
 638          * @param int $err ERR_* constant
 639          * @since 1.23
 640          */
 641         protected function setLastError( $err ) {
 642                 $this->lastError = $err;
 643         }
 644
 645         /**
 646          * Let a callback be run to avoid wasting time on special blocking calls
 647          *
 648          * The callbacks may or may not be called ever, in any particular order.
 649          * They are likely to be invoked when something WRITE_SYNC is used used.
 650          * They should follow a caching pattern as shown below, so that any code
 651          * using the word will get it's result no matter what happens.
 652          * @code
 653          *     $result = null;
 654          *     $workCallback = function () use ( &$result ) {
 655          *         if ( !$result ) {
 656          *             $result = ....
 657          *         }
 658          *         return $result;
 659          *     }
 660          * @endcode
 661          *
 662          * @param callable $workCallback
 663          * @since 1.28
 664          */
 665         public function addBusyCallback( callable $workCallback ) {
 666                 $this->busyCallbacks[] = $workCallback;
 667         }
 668
 669         /**
 670          * Modify a cache update operation array for EventRelayer::notify()
 671          *
 672          * This is used for relayed writes, e.g. for broadcasting a change
 673          * to multiple data-centers. If the array contains a 'val' field
 674          * then the command involves setting a key to that value. Note that
 675          * for simplicity, 'val' is always a simple scalar value. This method
 676          * is used to possibly serialize the value and add any cache-specific
 677          * key/values needed for the relayer daemon (e.g. memcached flags).
 678          *
 679          * @param array $event
 680          * @return array
 681          * @since 1.26
 682          */
 683         public function modifySimpleRelayEvent( array $event ) {
 684                 return $event;
 685         }
 686
 687         /**
 688          * @param string $text
 689          */
 690         protected function debug( $text ) {
 691                 if ( $this->debugMode ) {
 692                         $this->logger->debug( "{class} debug: $text", [
 693                                 'class' => static::class,
 694                         ] );
 695                 }
 696         }
 697
 698         /**
 699          * Convert an optionally relative time to an absolute time
 700          * @param int $exptime
 701          * @return int
 702          */
 703         protected function convertExpiry( $exptime ) {
 704                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 705                         return time() + $exptime;
 706                 } else {
 707                         return $exptime;
 708                 }
 709         }
 710
 711         /**
 712          * Convert an optionally absolute expiry time to a relative time. If an
 713          * absolute time is specified which is in the past, use a short expiry time.
 714          *
 715          * @param int $exptime
 716          * @return int
 717          */
 718         protected function convertToRelative( $exptime ) {
 719                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 720                         $exptime -= time();
 721                         if ( $exptime <= 0 ) {
 722                                 $exptime = 1;
 723                         }
 724                         return $exptime;
 725                 } else {
 726                         return $exptime;
 727                 }
 728         }
 729
 730         /**
 731          * Check if a value is an integer
 732          *
 733          * @param mixed $value
 734          * @return bool
 735          */
 736         protected function isInteger( $value ) {
 737                 return ( is_int( $value ) || ctype_digit( $value ) );
 738         }
 739
 740         /**
 741          * Construct a cache key.
 742          *
 743          * @since 1.27
 744          * @param string $keyspace
 745          * @param array $args
 746          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 747          */
 748         public function makeKeyInternal( $keyspace, $args ) {
 749                 $key = $keyspace;
 750                 foreach ( $args as $arg ) {
 751                         $arg = str_replace( ':', '%3A', $arg );
 752                         $key = $key . ':' . $arg;
 753                 }
 754                 return strtr( $key, ' ', '_' );
 755         }
 756
 757         /**
 758          * Make a global cache key.
 759          *
 760          * @since 1.27
 761          * @param string $class Key class
 762          * @param string $component [optional] Key component (starting with a key collection name)
 763          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 764          */
 765         public function makeGlobalKey( $class, $component = null ) {
 766                 return $this->makeKeyInternal( 'global', func_get_args() );
 767         }
 768
 769         /**
 770          * Make a cache key, scoped to this instance's keyspace.
 771          *
 772          * @since 1.27
 773          * @param string $class Key class
 774          * @param string $component [optional] Key component (starting with a key collection name)
 775          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 776          */
 777         public function makeKey( $class, $component = null ) {
 778                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 779         }
 780
 781         /**
 782          * @param int $flag ATTR_* class constant
 783          * @return int QOS_* class constant
 784          * @since 1.28
 785          */
 786         public function getQoS( $flag ) {
 787                 return isset( $this->attrMap[$flag] ) ? $this->attrMap[$flag] : self::QOS_UNKNOWN;
 788         }
 789
 790         /**
 791          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 792          *
 793          * @param BagOStuff[] $bags
 794          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 795          */
 796         protected function mergeFlagMaps( array $bags ) {
 797                 $map = [];
 798                 foreach ( $bags as $bag ) {
 799                         foreach ( $bag->attrMap as $attr => $rank ) {
 800                                 if ( isset( $map[$attr] ) ) {
 801                                         $map[$attr] = min( $map[$attr], $rank );
 802                                 } else {
 803                                         $map[$attr] = $rank;
 804                                 }
 805                         }
 806                 }
 807
 808                 return $map;
 809         }
 810 }