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
  33 /**
  34  * interface is intended to be more or less compatible with
  35  * the PHP memcached client.
  36  *
  37  * backends for local hash array and SQL table included:
  38  * @code
  39  *   $bag = new HashBagOStuff();
  40  *   $bag = new SqlBagOStuff(); # connect to db first
  41  * @endcode
  42  *
  43  * @ingroup Cache
  44  */
  45 abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
  46         /** @var array[] Lock tracking */
  47         protected $locks = [];
  48
  49         /** @var integer ERR_* class constant */
  50         protected $lastError = self::ERR_NONE;
  51
  52         /** @var string */
  53         protected $keyspace = 'local';
  54
  55         /** @var LoggerInterface */
  56         protected $logger;
  57
  58         /** @var callback|null */
  59         protected $asyncHandler;
  60
  61         /** @var bool */
  62         private $debugMode = false;
  63
  64         /** @var array */
  65         private $duplicateKeyLookups = [];
  66
  67         /** @var bool */
  68         private $reportDupes = false;
  69
  70         /** @var bool */
  71         private $dupeTrackScheduled = false;
  72
  73         /** @var integer[] 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          * @param array $params
  98          */
  99         public function __construct( array $params = [] ) {
 100                 if ( isset( $params['logger'] ) ) {
 101                         $this->setLogger( $params['logger'] );
 102                 } else {
 103                         $this->setLogger( new NullLogger() );
 104                 }
 105
 106                 if ( isset( $params['keyspace'] ) ) {
 107                         $this->keyspace = $params['keyspace'];
 108                 }
 109
 110                 $this->asyncHandler = isset( $params['asyncHandler'] )
 111                         ? $params['asyncHandler']
 112                         : null;
 113
 114                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 115                         $this->reportDupes = true;
 116                 }
 117         }
 118
 119         /**
 120          * @param LoggerInterface $logger
 121          * @return null
 122          */
 123         public function setLogger( LoggerInterface $logger ) {
 124                 $this->logger = $logger;
 125         }
 126
 127         /**
 128          * @param bool $bool
 129          */
 130         public function setDebug( $bool ) {
 131                 $this->debugMode = $bool;
 132         }
 133
 134         /**
 135          * Get an item with the given key, regenerating and setting it if not found
 136          *
 137          * If the callback returns false, then nothing is stored.
 138          *
 139          * @param string $key
 140          * @param int $ttl Time-to-live (seconds)
 141          * @param callable $callback Callback that derives the new value
 142          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 143          * @return mixed The cached value if found or the result of $callback otherwise
 144          * @since 1.27
 145          */
 146         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 147                 $value = $this->get( $key, $flags );
 148
 149                 if ( $value === false ) {
 150                         if ( !is_callable( $callback ) ) {
 151                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 152                         }
 153                         $value = call_user_func( $callback );
 154                         if ( $value !== false ) {
 155                                 $this->set( $key, $value, $ttl );
 156                         }
 157                 }
 158
 159                 return $value;
 160         }
 161
 162         /**
 163          * Get an item with the given key
 164          *
 165          * If the key includes a determistic input hash (e.g. the key can only have
 166          * the correct value) or complete staleness checks are handled by the caller
 167          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 168          * This lets tiered backends know they can safely upgrade a cached value to
 169          * higher tiers using standard TTLs.
 170          *
 171          * @param string $key
 172          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 173          * @param integer $oldFlags [unused]
 174          * @return mixed Returns false on failure and if the item does not exist
 175          */
 176         public function get( $key, $flags = 0, $oldFlags = null ) {
 177                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 178                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 179
 180                 $this->trackDuplicateKeys( $key );
 181
 182                 return $this->doGet( $key, $flags );
 183         }
 184
 185         /**
 186          * Track the number of times that a given key has been used.
 187          * @param string $key
 188          */
 189         private function trackDuplicateKeys( $key ) {
 190                 if ( !$this->reportDupes ) {
 191                         return;
 192                 }
 193
 194                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 195                         // Track that we have seen this key. This N-1 counting style allows
 196                         // easy filtering with array_filter() later.
 197                         $this->duplicateKeyLookups[$key] = 0;
 198                 } else {
 199                         $this->duplicateKeyLookups[$key] += 1;
 200
 201                         if ( $this->dupeTrackScheduled === false ) {
 202                                 $this->dupeTrackScheduled = true;
 203                                 // Schedule a callback that logs keys processed more than once by get().
 204                                 call_user_func( $this->asyncHandler, function () {
 205                                         $dups = array_filter( $this->duplicateKeyLookups );
 206                                         foreach ( $dups as $key => $count ) {
 207                                                 $this->logger->warning(
 208                                                         'Duplicate get(): "{key}" fetched {count} times',
 209                                                         // Count is N-1 of the actual lookup count
 210                                                         [ 'key' => $key, 'count' => $count + 1, ]
 211                                                 );
 212                                         }
 213                                 } );
 214                         }
 215                 }
 216         }
 217
 218         /**
 219          * @param string $key
 220          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 221          * @return mixed Returns false on failure and if the item does not exist
 222          */
 223         abstract protected function doGet( $key, $flags = 0 );
 224
 225         /**
 226          * @note: This method is only needed if merge() uses mergeViaCas()
 227          *
 228          * @param string $key
 229          * @param mixed $casToken
 230          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 231          * @return mixed Returns false on failure and if the item does not exist
 232          * @throws Exception
 233          */
 234         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 235                 throw new Exception( __METHOD__ . ' not implemented.' );
 236         }
 237
 238         /**
 239          * Set an item
 240          *
 241          * @param string $key
 242          * @param mixed $value
 243          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 244          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 245          * @return bool Success
 246          */
 247         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 248
 249         /**
 250          * Delete an item
 251          *
 252          * @param string $key
 253          * @return bool True if the item was deleted or not found, false on failure
 254          */
 255         abstract public function delete( $key );
 256
 257         /**
 258          * Merge changes into the existing cache value (possibly creating a new one)
 259          *
 260          * The callback function returns the new value given the current value
 261          * (which will be false if not present), and takes the arguments:
 262          * (this BagOStuff, cache key, current value, TTL).
 263          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 264          *
 265          * @param string $key
 266          * @param callable $callback Callback method to be executed
 267          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 268          * @param int $attempts The amount of times to attempt a merge in case of failure
 269          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 270          * @return bool Success
 271          * @throws InvalidArgumentException
 272          */
 273         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 274                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 275         }
 276
 277         /**
 278          * @see BagOStuff::merge()
 279          *
 280          * @param string $key
 281          * @param callable $callback Callback method to be executed
 282          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 283          * @param int $attempts The amount of times to attempt a merge in case of failure
 284          * @return bool Success
 285          */
 286         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 287                 do {
 288                         $this->clearLastError();
 289                         $reportDupes = $this->reportDupes;
 290                         $this->reportDupes = false;
 291                         $casToken = null; // passed by reference
 292                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 293                         $this->reportDupes = $reportDupes;
 294
 295                         if ( $this->getLastError() ) {
 296                                 return false; // don't spam retries (retry only on races)
 297                         }
 298
 299                         // Derive the new value from the old value
 300                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 301
 302                         $this->clearLastError();
 303                         if ( $value === false ) {
 304                                 $success = true; // do nothing
 305                         } elseif ( $currentValue === false ) {
 306                                 // Try to create the key, failing if it gets created in the meantime
 307                                 $success = $this->add( $key, $value, $exptime );
 308                         } else {
 309                                 // Try to update the key, failing if it gets changed in the meantime
 310                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 311                         }
 312                         if ( $this->getLastError() ) {
 313                                 return false; // IO error; don't spam retries
 314                         }
 315                 } while ( !$success && --$attempts );
 316
 317                 return $success;
 318         }
 319
 320         /**
 321          * Check and set an item
 322          *
 323          * @param mixed $casToken
 324          * @param string $key
 325          * @param mixed $value
 326          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 327          * @return bool Success
 328          * @throws Exception
 329          */
 330         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 331                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 332         }
 333
 334         /**
 335          * @see BagOStuff::merge()
 336          *
 337          * @param string $key
 338          * @param callable $callback Callback method to be executed
 339          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 340          * @param int $attempts The amount of times to attempt a merge in case of failure
 341          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 342          * @return bool Success
 343          */
 344         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 345                 if ( !$this->lock( $key, 6 ) ) {
 346                         return false;
 347                 }
 348
 349                 $this->clearLastError();
 350                 $reportDupes = $this->reportDupes;
 351                 $this->reportDupes = false;
 352                 $currentValue = $this->get( $key, self::READ_LATEST );
 353                 $this->reportDupes = $reportDupes;
 354
 355                 if ( $this->getLastError() ) {
 356                         $success = false;
 357                 } else {
 358                         // Derive the new value from the old value
 359                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 360                         if ( $value === false ) {
 361                                 $success = true; // do nothing
 362                         } else {
 363                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 364                         }
 365                 }
 366
 367                 if ( !$this->unlock( $key ) ) {
 368                         // this should never happen
 369                         trigger_error( "Could not release lock for key '$key'." );
 370                 }
 371
 372                 return $success;
 373         }
 374
 375         /**
 376          * Reset the TTL on a key if it exists
 377          *
 378          * @param string $key
 379          * @param int $expiry
 380          * @return bool Success Returns false if there is no key
 381          * @since 1.28
 382          */
 383         public function changeTTL( $key, $expiry = 0 ) {
 384                 $value = $this->get( $key );
 385
 386                 return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
 387         }
 388
 389         /**
 390          * Acquire an advisory lock on a key string
 391          *
 392          * Note that if reentry is enabled, duplicate calls ignore $expiry
 393          *
 394          * @param string $key
 395          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 396          * @param int $expiry Lock expiry [optional]; 1 day maximum
 397          * @param string $rclass Allow reentry if set and the current lock used this value
 398          * @return bool Success
 399          */
 400         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 401                 // Avoid deadlocks and allow lock reentry if specified
 402                 if ( isset( $this->locks[$key] ) ) {
 403                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 404                                 ++$this->locks[$key]['depth'];
 405                                 return true;
 406                         } else {
 407                                 return false;
 408                         }
 409                 }
 410
 411                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 412
 413                 $this->clearLastError();
 414                 $timestamp = microtime( true ); // starting UNIX timestamp
 415                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 416                         $locked = true;
 417                 } elseif ( $this->getLastError() || $timeout <= 0 ) {
 418                         $locked = false; // network partition or non-blocking
 419                 } else {
 420                         // Estimate the RTT (us); use 1ms minimum for sanity
 421                         $uRTT = max( 1e3, ceil( 1e6 * ( microtime( true ) - $timestamp ) ) );
 422                         $sleep = 2 * $uRTT; // rough time to do get()+set()
 423
 424                         $attempts = 0; // failed attempts
 425                         do {
 426                                 if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
 427                                         // Exponentially back off after failed attempts to avoid network spam.
 428                                         // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 429                                         $sleep *= 2;
 430                                 }
 431                                 usleep( $sleep ); // back off
 432                                 $this->clearLastError();
 433                                 $locked = $this->add( "{$key}:lock", 1, $expiry );
 434                                 if ( $this->getLastError() ) {
 435                                         $locked = false; // network partition
 436                                         break;
 437                                 }
 438                         } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 439                 }
 440
 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 = .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 integer $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          * Modify a cache update operation array for EventRelayer::notify()
 647          *
 648          * This is used for relayed writes, e.g. for broadcasting a change
 649          * to multiple data-centers. If the array contains a 'val' field
 650          * then the command involves setting a key to that value. Note that
 651          * for simplicity, 'val' is always a simple scalar value. This method
 652          * is used to possibly serialize the value and add any cache-specific
 653          * key/values needed for the relayer daemon (e.g. memcached flags).
 654          *
 655          * @param array $event
 656          * @return array
 657          * @since 1.26
 658          */
 659         public function modifySimpleRelayEvent( array $event ) {
 660                 return $event;
 661         }
 662
 663         /**
 664          * @param string $text
 665          */
 666         protected function debug( $text ) {
 667                 if ( $this->debugMode ) {
 668                         $this->logger->debug( "{class} debug: $text", [
 669                                 'class' => get_class( $this ),
 670                         ] );
 671                 }
 672         }
 673
 674         /**
 675          * Convert an optionally relative time to an absolute time
 676          * @param int $exptime
 677          * @return int
 678          */
 679         protected function convertExpiry( $exptime ) {
 680                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 681                         return time() + $exptime;
 682                 } else {
 683                         return $exptime;
 684                 }
 685         }
 686
 687         /**
 688          * Convert an optionally absolute expiry time to a relative time. If an
 689          * absolute time is specified which is in the past, use a short expiry time.
 690          *
 691          * @param int $exptime
 692          * @return int
 693          */
 694         protected function convertToRelative( $exptime ) {
 695                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 696                         $exptime -= time();
 697                         if ( $exptime <= 0 ) {
 698                                 $exptime = 1;
 699                         }
 700                         return $exptime;
 701                 } else {
 702                         return $exptime;
 703                 }
 704         }
 705
 706         /**
 707          * Check if a value is an integer
 708          *
 709          * @param mixed $value
 710          * @return bool
 711          */
 712         protected function isInteger( $value ) {
 713                 return ( is_int( $value ) || ctype_digit( $value ) );
 714         }
 715
 716         /**
 717          * Construct a cache key.
 718          *
 719          * @since 1.27
 720          * @param string $keyspace
 721          * @param array $args
 722          * @return string
 723          */
 724         public function makeKeyInternal( $keyspace, $args ) {
 725                 $key = $keyspace;
 726                 foreach ( $args as $arg ) {
 727                         $arg = str_replace( ':', '%3A', $arg );
 728                         $key = $key . ':' . $arg;
 729                 }
 730                 return strtr( $key, ' ', '_' );
 731         }
 732
 733         /**
 734          * Make a global cache key.
 735          *
 736          * @since 1.27
 737          * @param string ... Key component (variadic)
 738          * @return string
 739          */
 740         public function makeGlobalKey() {
 741                 return $this->makeKeyInternal( 'global', func_get_args() );
 742         }
 743
 744         /**
 745          * Make a cache key, scoped to this instance's keyspace.
 746          *
 747          * @since 1.27
 748          * @param string ... Key component (variadic)
 749          * @return string
 750          */
 751         public function makeKey() {
 752                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 753         }
 754
 755         /**
 756          * @param integer $flag ATTR_* class constant
 757          * @return integer QOS_* class constant
 758          * @since 1.28
 759          */
 760         public function getQoS( $flag ) {
 761                 return isset( $this->attrMap[$flag] ) ? $this->attrMap[$flag] : self::QOS_UNKNOWN;
 762         }
 763
 764         /**
 765          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 766          *
 767          * @param BagOStuff[] $bags
 768          * @return integer[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 769          */
 770         protected function mergeFlagMaps( array $bags ) {
 771                 $map = [];
 772                 foreach ( $bags as $bag ) {
 773                         foreach ( $bag->attrMap as $attr => $rank ) {
 774                                 if ( isset( $map[$attr] ) ) {
 775                                         $map[$attr] = min( $map[$attr], $rank );
 776                                 } else {
 777                                         $map[$attr] = $rank;
 778                                 }
 779                         }
 780                 }
 781
 782                 return $map;
 783         }
 784 }