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 float|null */
  74         private $wallClockOverride;
  75
  76         /** @var int[] Map of (ATTR_* class constant => QOS_* class constant) */
  77         protected $attrMap = [];
  78
  79         /** Possible values for getLastError() */
  80         const ERR_NONE = 0; // no error
  81         const ERR_NO_RESPONSE = 1; // no response
  82         const ERR_UNREACHABLE = 2; // can't connect
  83         const ERR_UNEXPECTED = 3; // response gave some error
  84
  85         /** Bitfield constants for get()/getMulti() */
  86         const READ_LATEST = 1; // use latest data for replicated stores
  87         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  88         /** Bitfield constants for set()/merge() */
  89         const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
  90         const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache
  91
  92         /**
  93          * $params include:
  94          *   - logger: Psr\Log\LoggerInterface instance
  95          *   - keyspace: Default keyspace for $this->makeKey()
  96          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
  97          *      In CLI mode, it should run the task immediately.
  98          *   - reportDupes: Whether to emit warning log messages for all keys that were
  99          *      requested more than once (requires an asyncHandler).
 100          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
 101          * @param array $params
 102          */
 103         public function __construct( array $params = [] ) {
 104                 if ( isset( $params['logger'] ) ) {
 105                         $this->setLogger( $params['logger'] );
 106                 } else {
 107                         $this->setLogger( new NullLogger() );
 108                 }
 109
 110                 if ( isset( $params['keyspace'] ) ) {
 111                         $this->keyspace = $params['keyspace'];
 112                 }
 113
 114                 $this->asyncHandler = isset( $params['asyncHandler'] )
 115                         ? $params['asyncHandler']
 116                         : null;
 117
 118                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 119                         $this->reportDupes = true;
 120                 }
 121
 122                 $this->syncTimeout = isset( $params['syncTimeout'] ) ? $params['syncTimeout'] : 3;
 123         }
 124
 125         /**
 126          * @param LoggerInterface $logger
 127          * @return null
 128          */
 129         public function setLogger( LoggerInterface $logger ) {
 130                 $this->logger = $logger;
 131         }
 132
 133         /**
 134          * @param bool $bool
 135          */
 136         public function setDebug( $bool ) {
 137                 $this->debugMode = $bool;
 138         }
 139
 140         /**
 141          * Get an item with the given key, regenerating and setting it if not found
 142          *
 143          * If the callback returns false, then nothing is stored.
 144          *
 145          * @param string $key
 146          * @param int $ttl Time-to-live (seconds)
 147          * @param callable $callback Callback that derives the new value
 148          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 149          * @return mixed The cached value if found or the result of $callback otherwise
 150          * @since 1.27
 151          */
 152         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 153                 $value = $this->get( $key, $flags );
 154
 155                 if ( $value === false ) {
 156                         if ( !is_callable( $callback ) ) {
 157                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 158                         }
 159                         $value = call_user_func( $callback );
 160                         if ( $value !== false ) {
 161                                 $this->set( $key, $value, $ttl );
 162                         }
 163                 }
 164
 165                 return $value;
 166         }
 167
 168         /**
 169          * Get an item with the given key
 170          *
 171          * If the key includes a determistic input hash (e.g. the key can only have
 172          * the correct value) or complete staleness checks are handled by the caller
 173          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 174          * This lets tiered backends know they can safely upgrade a cached value to
 175          * higher tiers using standard TTLs.
 176          *
 177          * @param string $key
 178          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 179          * @param int $oldFlags [unused]
 180          * @return mixed Returns false on failure and if the item does not exist
 181          */
 182         public function get( $key, $flags = 0, $oldFlags = null ) {
 183                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 184                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 185
 186                 $this->trackDuplicateKeys( $key );
 187
 188                 return $this->doGet( $key, $flags );
 189         }
 190
 191         /**
 192          * Track the number of times that a given key has been used.
 193          * @param string $key
 194          */
 195         private function trackDuplicateKeys( $key ) {
 196                 if ( !$this->reportDupes ) {
 197                         return;
 198                 }
 199
 200                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 201                         // Track that we have seen this key. This N-1 counting style allows
 202                         // easy filtering with array_filter() later.
 203                         $this->duplicateKeyLookups[$key] = 0;
 204                 } else {
 205                         $this->duplicateKeyLookups[$key] += 1;
 206
 207                         if ( $this->dupeTrackScheduled === false ) {
 208                                 $this->dupeTrackScheduled = true;
 209                                 // Schedule a callback that logs keys processed more than once by get().
 210                                 call_user_func( $this->asyncHandler, function () {
 211                                         $dups = array_filter( $this->duplicateKeyLookups );
 212                                         foreach ( $dups as $key => $count ) {
 213                                                 $this->logger->warning(
 214                                                         'Duplicate get(): "{key}" fetched {count} times',
 215                                                         // Count is N-1 of the actual lookup count
 216                                                         [ 'key' => $key, 'count' => $count + 1, ]
 217                                                 );
 218                                         }
 219                                 } );
 220                         }
 221                 }
 222         }
 223
 224         /**
 225          * @param string $key
 226          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 227          * @return mixed Returns false on failure and if the item does not exist
 228          */
 229         abstract protected function doGet( $key, $flags = 0 );
 230
 231         /**
 232          * @note: This method is only needed if merge() uses mergeViaCas()
 233          *
 234          * @param string $key
 235          * @param mixed &$casToken
 236          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 237          * @return mixed Returns false on failure and if the item does not exist
 238          * @throws Exception
 239          */
 240         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 241                 throw new Exception( __METHOD__ . ' not implemented.' );
 242         }
 243
 244         /**
 245          * Set an item
 246          *
 247          * @param string $key
 248          * @param mixed $value
 249          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 250          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 251          * @return bool Success
 252          */
 253         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 254
 255         /**
 256          * Delete an item
 257          *
 258          * @param string $key
 259          * @return bool True if the item was deleted or not found, false on failure
 260          */
 261         abstract public function delete( $key );
 262
 263         /**
 264          * Merge changes into the existing cache value (possibly creating a new one)
 265          *
 266          * The callback function returns the new value given the current value
 267          * (which will be false if not present), and takes the arguments:
 268          * (this BagOStuff, cache key, current value, TTL).
 269          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 270          *
 271          * @param string $key
 272          * @param callable $callback Callback method to be executed
 273          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 274          * @param int $attempts The amount of times to attempt a merge in case of failure
 275          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 276          * @return bool Success
 277          * @throws InvalidArgumentException
 278          */
 279         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 280                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 281         }
 282
 283         /**
 284          * @see BagOStuff::merge()
 285          *
 286          * @param string $key
 287          * @param callable $callback Callback method to be executed
 288          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 289          * @param int $attempts The amount of times to attempt a merge in case of failure
 290          * @return bool Success
 291          */
 292         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 293                 do {
 294                         $this->clearLastError();
 295                         $reportDupes = $this->reportDupes;
 296                         $this->reportDupes = false;
 297                         $casToken = null; // passed by reference
 298                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 299                         $this->reportDupes = $reportDupes;
 300
 301                         if ( $this->getLastError() ) {
 302                                 return false; // don't spam retries (retry only on races)
 303                         }
 304
 305                         // Derive the new value from the old value
 306                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 307
 308                         $this->clearLastError();
 309                         if ( $value === false ) {
 310                                 $success = true; // do nothing
 311                         } elseif ( $currentValue === false ) {
 312                                 // Try to create the key, failing if it gets created in the meantime
 313                                 $success = $this->add( $key, $value, $exptime );
 314                         } else {
 315                                 // Try to update the key, failing if it gets changed in the meantime
 316                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 317                         }
 318                         if ( $this->getLastError() ) {
 319                                 return false; // IO error; don't spam retries
 320                         }
 321                 } while ( !$success && --$attempts );
 322
 323                 return $success;
 324         }
 325
 326         /**
 327          * Check and set an item
 328          *
 329          * @param mixed $casToken
 330          * @param string $key
 331          * @param mixed $value
 332          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 333          * @return bool Success
 334          * @throws Exception
 335          */
 336         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 337                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 338         }
 339
 340         /**
 341          * @see BagOStuff::merge()
 342          *
 343          * @param string $key
 344          * @param callable $callback Callback method to be executed
 345          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 346          * @param int $attempts The amount of times to attempt a merge in case of failure
 347          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 348          * @return bool Success
 349          */
 350         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 351                 if ( !$this->lock( $key, 6 ) ) {
 352                         return false;
 353                 }
 354
 355                 $this->clearLastError();
 356                 $reportDupes = $this->reportDupes;
 357                 $this->reportDupes = false;
 358                 $currentValue = $this->get( $key, self::READ_LATEST );
 359                 $this->reportDupes = $reportDupes;
 360
 361                 if ( $this->getLastError() ) {
 362                         $success = false;
 363                 } else {
 364                         // Derive the new value from the old value
 365                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 366                         if ( $value === false ) {
 367                                 $success = true; // do nothing
 368                         } else {
 369                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 370                         }
 371                 }
 372
 373                 if ( !$this->unlock( $key ) ) {
 374                         // this should never happen
 375                         trigger_error( "Could not release lock for key '$key'." );
 376                 }
 377
 378                 return $success;
 379         }
 380
 381         /**
 382          * Reset the TTL on a key if it exists
 383          *
 384          * @param string $key
 385          * @param int $expiry
 386          * @return bool Success Returns false if there is no key
 387          * @since 1.28
 388          */
 389         public function changeTTL( $key, $expiry = 0 ) {
 390                 $value = $this->get( $key );
 391
 392                 return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
 393         }
 394
 395         /**
 396          * Acquire an advisory lock on a key string
 397          *
 398          * Note that if reentry is enabled, duplicate calls ignore $expiry
 399          *
 400          * @param string $key
 401          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 402          * @param int $expiry Lock expiry [optional]; 1 day maximum
 403          * @param string $rclass Allow reentry if set and the current lock used this value
 404          * @return bool Success
 405          */
 406         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 407                 // Avoid deadlocks and allow lock reentry if specified
 408                 if ( isset( $this->locks[$key] ) ) {
 409                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 410                                 ++$this->locks[$key]['depth'];
 411                                 return true;
 412                         } else {
 413                                 return false;
 414                         }
 415                 }
 416
 417                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 418                 $loop = new WaitConditionLoop(
 419                         function () use ( $key, $timeout, $expiry ) {
 420                                 $this->clearLastError();
 421                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 422                                         return true; // locked!
 423                                 } elseif ( $this->getLastError() ) {
 424                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 425                                 }
 426
 427                                 return WaitConditionLoop::CONDITION_CONTINUE;
 428                         },
 429                         $timeout
 430                 );
 431
 432                 $locked = ( $loop->invoke() === $loop::CONDITION_REACHED );
 433                 if ( $locked ) {
 434                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 435                 }
 436
 437                 return $locked;
 438         }
 439
 440         /**
 441          * Release an advisory lock on a key string
 442          *
 443          * @param string $key
 444          * @return bool Success
 445          */
 446         public function unlock( $key ) {
 447                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 448                         unset( $this->locks[$key] );
 449
 450                         return $this->delete( "{$key}:lock" );
 451                 }
 452
 453                 return true;
 454         }
 455
 456         /**
 457          * Get a lightweight exclusive self-unlocking lock
 458          *
 459          * Note that the same lock cannot be acquired twice.
 460          *
 461          * This is useful for task de-duplication or to avoid obtrusive
 462          * (though non-corrupting) DB errors like INSERT key conflicts
 463          * or deadlocks when using LOCK IN SHARE MODE.
 464          *
 465          * @param string $key
 466          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 467          * @param int $expiry Lock expiry [optional]; 1 day maximum
 468          * @param string $rclass Allow reentry if set and the current lock used this value
 469          * @return ScopedCallback|null Returns null on failure
 470          * @since 1.26
 471          */
 472         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 473                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 474
 475                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 476                         return null;
 477                 }
 478
 479                 $lSince = $this->getCurrentTime(); // lock timestamp
 480
 481                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 482                         $latency = 0.050; // latency skew (err towards keeping lock present)
 483                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 484                         if ( ( $age + $latency ) >= $expiry ) {
 485                                 $this->logger->warning( "Lock for $key held too long ($age sec)." );
 486                                 return; // expired; it's not "safe" to delete the key
 487                         }
 488                         $this->unlock( $key );
 489                 } );
 490         }
 491
 492         /**
 493          * Delete all objects expiring before a certain date.
 494          * @param string $date The reference date in MW format
 495          * @param callable|bool $progressCallback Optional, a function which will be called
 496          *     regularly during long-running operations with the percentage progress
 497          *     as the first parameter.
 498          *
 499          * @return bool Success, false if unimplemented
 500          */
 501         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 502                 // stub
 503                 return false;
 504         }
 505
 506         /**
 507          * Get an associative array containing the item for each of the keys that have items.
 508          * @param array $keys List of strings
 509          * @param int $flags Bitfield; supports READ_LATEST [optional]
 510          * @return array
 511          */
 512         public function getMulti( array $keys, $flags = 0 ) {
 513                 $res = [];
 514                 foreach ( $keys as $key ) {
 515                         $val = $this->get( $key );
 516                         if ( $val !== false ) {
 517                                 $res[$key] = $val;
 518                         }
 519                 }
 520                 return $res;
 521         }
 522
 523         /**
 524          * Batch insertion
 525          * @param array $data $key => $value assoc array
 526          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 527          * @return bool Success
 528          * @since 1.24
 529          */
 530         public function setMulti( array $data, $exptime = 0 ) {
 531                 $res = true;
 532                 foreach ( $data as $key => $value ) {
 533                         if ( !$this->set( $key, $value, $exptime ) ) {
 534                                 $res = false;
 535                         }
 536                 }
 537                 return $res;
 538         }
 539
 540         /**
 541          * @param string $key
 542          * @param mixed $value
 543          * @param int $exptime
 544          * @return bool Success
 545          */
 546         public function add( $key, $value, $exptime = 0 ) {
 547                 if ( $this->get( $key ) === false ) {
 548                         return $this->set( $key, $value, $exptime );
 549                 }
 550                 return false; // key already set
 551         }
 552
 553         /**
 554          * Increase stored value of $key by $value while preserving its TTL
 555          * @param string $key Key to increase
 556          * @param int $value Value to add to $key (Default 1)
 557          * @return int|bool New value or false on failure
 558          */
 559         public function incr( $key, $value = 1 ) {
 560                 if ( !$this->lock( $key ) ) {
 561                         return false;
 562                 }
 563                 $n = $this->get( $key );
 564                 if ( $this->isInteger( $n ) ) { // key exists?
 565                         $n += intval( $value );
 566                         $this->set( $key, max( 0, $n ) ); // exptime?
 567                 } else {
 568                         $n = false;
 569                 }
 570                 $this->unlock( $key );
 571
 572                 return $n;
 573         }
 574
 575         /**
 576          * Decrease stored value of $key by $value while preserving its TTL
 577          * @param string $key
 578          * @param int $value
 579          * @return int|bool New value or false on failure
 580          */
 581         public function decr( $key, $value = 1 ) {
 582                 return $this->incr( $key, - $value );
 583         }
 584
 585         /**
 586          * Increase stored value of $key by $value while preserving its TTL
 587          *
 588          * This will create the key with value $init and TTL $ttl instead if not present
 589          *
 590          * @param string $key
 591          * @param int $ttl
 592          * @param int $value
 593          * @param int $init
 594          * @return int|bool New value or false on failure
 595          * @since 1.24
 596          */
 597         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 598                 $newValue = $this->incr( $key, $value );
 599                 if ( $newValue === false ) {
 600                         // No key set; initialize
 601                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 602                 }
 603                 if ( $newValue === false ) {
 604                         // Raced out initializing; increment
 605                         $newValue = $this->incr( $key, $value );
 606                 }
 607
 608                 return $newValue;
 609         }
 610
 611         /**
 612          * Get the "last error" registered; clearLastError() should be called manually
 613          * @return int ERR_* constant for the "last error" registry
 614          * @since 1.23
 615          */
 616         public function getLastError() {
 617                 return $this->lastError;
 618         }
 619
 620         /**
 621          * Clear the "last error" registry
 622          * @since 1.23
 623          */
 624         public function clearLastError() {
 625                 $this->lastError = self::ERR_NONE;
 626         }
 627
 628         /**
 629          * Set the "last error" registry
 630          * @param int $err ERR_* constant
 631          * @since 1.23
 632          */
 633         protected function setLastError( $err ) {
 634                 $this->lastError = $err;
 635         }
 636
 637         /**
 638          * Let a callback be run to avoid wasting time on special blocking calls
 639          *
 640          * The callbacks may or may not be called ever, in any particular order.
 641          * They are likely to be invoked when something WRITE_SYNC is used used.
 642          * They should follow a caching pattern as shown below, so that any code
 643          * using the word will get it's result no matter what happens.
 644          * @code
 645          *     $result = null;
 646          *     $workCallback = function () use ( &$result ) {
 647          *         if ( !$result ) {
 648          *             $result = ....
 649          *         }
 650          *         return $result;
 651          *     }
 652          * @endcode
 653          *
 654          * @param callable $workCallback
 655          * @since 1.28
 656          */
 657         public function addBusyCallback( callable $workCallback ) {
 658                 $this->busyCallbacks[] = $workCallback;
 659         }
 660
 661         /**
 662          * Modify a cache update operation array for EventRelayer::notify()
 663          *
 664          * This is used for relayed writes, e.g. for broadcasting a change
 665          * to multiple data-centers. If the array contains a 'val' field
 666          * then the command involves setting a key to that value. Note that
 667          * for simplicity, 'val' is always a simple scalar value. This method
 668          * is used to possibly serialize the value and add any cache-specific
 669          * key/values needed for the relayer daemon (e.g. memcached flags).
 670          *
 671          * @param array $event
 672          * @return array
 673          * @since 1.26
 674          */
 675         public function modifySimpleRelayEvent( array $event ) {
 676                 return $event;
 677         }
 678
 679         /**
 680          * @param string $text
 681          */
 682         protected function debug( $text ) {
 683                 if ( $this->debugMode ) {
 684                         $this->logger->debug( "{class} debug: $text", [
 685                                 'class' => static::class,
 686                         ] );
 687                 }
 688         }
 689
 690         /**
 691          * Convert an optionally relative time to an absolute time
 692          * @param int $exptime
 693          * @return int
 694          */
 695         protected function convertExpiry( $exptime ) {
 696                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 697                         return (int)$this->getCurrentTime() + $exptime;
 698                 } else {
 699                         return $exptime;
 700                 }
 701         }
 702
 703         /**
 704          * Convert an optionally absolute expiry time to a relative time. If an
 705          * absolute time is specified which is in the past, use a short expiry time.
 706          *
 707          * @param int $exptime
 708          * @return int
 709          */
 710         protected function convertToRelative( $exptime ) {
 711                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 712                         $exptime -= (int)$this->getCurrentTime();
 713                         if ( $exptime <= 0 ) {
 714                                 $exptime = 1;
 715                         }
 716                         return $exptime;
 717                 } else {
 718                         return $exptime;
 719                 }
 720         }
 721
 722         /**
 723          * Check if a value is an integer
 724          *
 725          * @param mixed $value
 726          * @return bool
 727          */
 728         protected function isInteger( $value ) {
 729                 return ( is_int( $value ) || ctype_digit( $value ) );
 730         }
 731
 732         /**
 733          * Construct a cache key.
 734          *
 735          * @since 1.27
 736          * @param string $keyspace
 737          * @param array $args
 738          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 739          */
 740         public function makeKeyInternal( $keyspace, $args ) {
 741                 $key = $keyspace;
 742                 foreach ( $args as $arg ) {
 743                         $arg = str_replace( ':', '%3A', $arg );
 744                         $key = $key . ':' . $arg;
 745                 }
 746                 return strtr( $key, ' ', '_' );
 747         }
 748
 749         /**
 750          * Make a global cache key.
 751          *
 752          * @since 1.27
 753          * @param string $class Key class
 754          * @param string $component [optional] Key component (starting with a key collection name)
 755          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 756          */
 757         public function makeGlobalKey( $class, $component = null ) {
 758                 return $this->makeKeyInternal( 'global', func_get_args() );
 759         }
 760
 761         /**
 762          * Make a cache key, scoped to this instance's keyspace.
 763          *
 764          * @since 1.27
 765          * @param string $class Key class
 766          * @param string $component [optional] Key component (starting with a key collection name)
 767          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 768          */
 769         public function makeKey( $class, $component = null ) {
 770                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 771         }
 772
 773         /**
 774          * @param int $flag ATTR_* class constant
 775          * @return int QOS_* class constant
 776          * @since 1.28
 777          */
 778         public function getQoS( $flag ) {
 779                 return isset( $this->attrMap[$flag] ) ? $this->attrMap[$flag] : self::QOS_UNKNOWN;
 780         }
 781
 782         /**
 783          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 784          *
 785          * @param BagOStuff[] $bags
 786          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 787          */
 788         protected function mergeFlagMaps( array $bags ) {
 789                 $map = [];
 790                 foreach ( $bags as $bag ) {
 791                         foreach ( $bag->attrMap as $attr => $rank ) {
 792                                 if ( isset( $map[$attr] ) ) {
 793                                         $map[$attr] = min( $map[$attr], $rank );
 794                                 } else {
 795                                         $map[$attr] = $rank;
 796                                 }
 797                         }
 798                 }
 799
 800                 return $map;
 801         }
 802
 803         /**
 804          * @return float UNIX timestamp
 805          * @codeCoverageIgnore
 806          */
 807         protected function getCurrentTime() {
 808                 return $this->wallClockOverride ?: microtime( true );
 809         }
 810
 811         /**
 812          * @param float|null &$time Mock UNIX timestamp for testing
 813          * @codeCoverageIgnore
 814          */
 815         public function setMockTime( &$time ) {
 816                 $this->wallClockOverride =& $time;
 817         }
 818 }