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          * Acquire an advisory lock on a key string
 377          *
 378          * Note that if reentry is enabled, duplicate calls ignore $expiry
 379          *
 380          * @param string $key
 381          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 382          * @param int $expiry Lock expiry [optional]; 1 day maximum
 383          * @param string $rclass Allow reentry if set and the current lock used this value
 384          * @return bool Success
 385          */
 386         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 387                 // Avoid deadlocks and allow lock reentry if specified
 388                 if ( isset( $this->locks[$key] ) ) {
 389                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 390                                 ++$this->locks[$key]['depth'];
 391                                 return true;
 392                         } else {
 393                                 return false;
 394                         }
 395                 }
 396
 397                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 398
 399                 $this->clearLastError();
 400                 $timestamp = microtime( true ); // starting UNIX timestamp
 401                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 402                         $locked = true;
 403                 } elseif ( $this->getLastError() || $timeout <= 0 ) {
 404                         $locked = false; // network partition or non-blocking
 405                 } else {
 406                         // Estimate the RTT (us); use 1ms minimum for sanity
 407                         $uRTT = max( 1e3, ceil( 1e6 * ( microtime( true ) - $timestamp ) ) );
 408                         $sleep = 2 * $uRTT; // rough time to do get()+set()
 409
 410                         $attempts = 0; // failed attempts
 411                         do {
 412                                 if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
 413                                         // Exponentially back off after failed attempts to avoid network spam.
 414                                         // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 415                                         $sleep *= 2;
 416                                 }
 417                                 usleep( $sleep ); // back off
 418                                 $this->clearLastError();
 419                                 $locked = $this->add( "{$key}:lock", 1, $expiry );
 420                                 if ( $this->getLastError() ) {
 421                                         $locked = false; // network partition
 422                                         break;
 423                                 }
 424                         } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 425                 }
 426
 427                 if ( $locked ) {
 428                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 429                 }
 430
 431                 return $locked;
 432         }
 433
 434         /**
 435          * Release an advisory lock on a key string
 436          *
 437          * @param string $key
 438          * @return bool Success
 439          */
 440         public function unlock( $key ) {
 441                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 442                         unset( $this->locks[$key] );
 443
 444                         return $this->delete( "{$key}:lock" );
 445                 }
 446
 447                 return true;
 448         }
 449
 450         /**
 451          * Get a lightweight exclusive self-unlocking lock
 452          *
 453          * Note that the same lock cannot be acquired twice.
 454          *
 455          * This is useful for task de-duplication or to avoid obtrusive
 456          * (though non-corrupting) DB errors like INSERT key conflicts
 457          * or deadlocks when using LOCK IN SHARE MODE.
 458          *
 459          * @param string $key
 460          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 461          * @param int $expiry Lock expiry [optional]; 1 day maximum
 462          * @param string $rclass Allow reentry if set and the current lock used this value
 463          * @return ScopedCallback|null Returns null on failure
 464          * @since 1.26
 465          */
 466         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 467                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 468
 469                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 470                         return null;
 471                 }
 472
 473                 $lSince = microtime( true ); // lock timestamp
 474
 475                 return new ScopedCallback( function() use ( $key, $lSince, $expiry ) {
 476                         $latency = .050; // latency skew (err towards keeping lock present)
 477                         $age = ( microtime( true ) - $lSince + $latency );
 478                         if ( ( $age + $latency ) >= $expiry ) {
 479                                 $this->logger->warning( "Lock for $key held too long ($age sec)." );
 480                                 return; // expired; it's not "safe" to delete the key
 481                         }
 482                         $this->unlock( $key );
 483                 } );
 484         }
 485
 486         /**
 487          * Delete all objects expiring before a certain date.
 488          * @param string $date The reference date in MW format
 489          * @param callable|bool $progressCallback Optional, a function which will be called
 490          *     regularly during long-running operations with the percentage progress
 491          *     as the first parameter.
 492          *
 493          * @return bool Success, false if unimplemented
 494          */
 495         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 496                 // stub
 497                 return false;
 498         }
 499
 500         /**
 501          * Get an associative array containing the item for each of the keys that have items.
 502          * @param array $keys List of strings
 503          * @param integer $flags Bitfield; supports READ_LATEST [optional]
 504          * @return array
 505          */
 506         public function getMulti( array $keys, $flags = 0 ) {
 507                 $res = [];
 508                 foreach ( $keys as $key ) {
 509                         $val = $this->get( $key );
 510                         if ( $val !== false ) {
 511                                 $res[$key] = $val;
 512                         }
 513                 }
 514                 return $res;
 515         }
 516
 517         /**
 518          * Batch insertion
 519          * @param array $data $key => $value assoc array
 520          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 521          * @return bool Success
 522          * @since 1.24
 523          */
 524         public function setMulti( array $data, $exptime = 0 ) {
 525                 $res = true;
 526                 foreach ( $data as $key => $value ) {
 527                         if ( !$this->set( $key, $value, $exptime ) ) {
 528                                 $res = false;
 529                         }
 530                 }
 531                 return $res;
 532         }
 533
 534         /**
 535          * @param string $key
 536          * @param mixed $value
 537          * @param int $exptime
 538          * @return bool Success
 539          */
 540         public function add( $key, $value, $exptime = 0 ) {
 541                 if ( $this->get( $key ) === false ) {
 542                         return $this->set( $key, $value, $exptime );
 543                 }
 544                 return false; // key already set
 545         }
 546
 547         /**
 548          * Increase stored value of $key by $value while preserving its TTL
 549          * @param string $key Key to increase
 550          * @param int $value Value to add to $key (Default 1)
 551          * @return int|bool New value or false on failure
 552          */
 553         public function incr( $key, $value = 1 ) {
 554                 if ( !$this->lock( $key ) ) {
 555                         return false;
 556                 }
 557                 $n = $this->get( $key );
 558                 if ( $this->isInteger( $n ) ) { // key exists?
 559                         $n += intval( $value );
 560                         $this->set( $key, max( 0, $n ) ); // exptime?
 561                 } else {
 562                         $n = false;
 563                 }
 564                 $this->unlock( $key );
 565
 566                 return $n;
 567         }
 568
 569         /**
 570          * Decrease stored value of $key by $value while preserving its TTL
 571          * @param string $key
 572          * @param int $value
 573          * @return int|bool New value or false on failure
 574          */
 575         public function decr( $key, $value = 1 ) {
 576                 return $this->incr( $key, - $value );
 577         }
 578
 579         /**
 580          * Increase stored value of $key by $value while preserving its TTL
 581          *
 582          * This will create the key with value $init and TTL $ttl instead if not present
 583          *
 584          * @param string $key
 585          * @param int $ttl
 586          * @param int $value
 587          * @param int $init
 588          * @return int|bool New value or false on failure
 589          * @since 1.24
 590          */
 591         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 592                 $newValue = $this->incr( $key, $value );
 593                 if ( $newValue === false ) {
 594                         // No key set; initialize
 595                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 596                 }
 597                 if ( $newValue === false ) {
 598                         // Raced out initializing; increment
 599                         $newValue = $this->incr( $key, $value );
 600                 }
 601
 602                 return $newValue;
 603         }
 604
 605         /**
 606          * Get the "last error" registered; clearLastError() should be called manually
 607          * @return int ERR_* constant for the "last error" registry
 608          * @since 1.23
 609          */
 610         public function getLastError() {
 611                 return $this->lastError;
 612         }
 613
 614         /**
 615          * Clear the "last error" registry
 616          * @since 1.23
 617          */
 618         public function clearLastError() {
 619                 $this->lastError = self::ERR_NONE;
 620         }
 621
 622         /**
 623          * Set the "last error" registry
 624          * @param int $err ERR_* constant
 625          * @since 1.23
 626          */
 627         protected function setLastError( $err ) {
 628                 $this->lastError = $err;
 629         }
 630
 631         /**
 632          * Modify a cache update operation array for EventRelayer::notify()
 633          *
 634          * This is used for relayed writes, e.g. for broadcasting a change
 635          * to multiple data-centers. If the array contains a 'val' field
 636          * then the command involves setting a key to that value. Note that
 637          * for simplicity, 'val' is always a simple scalar value. This method
 638          * is used to possibly serialize the value and add any cache-specific
 639          * key/values needed for the relayer daemon (e.g. memcached flags).
 640          *
 641          * @param array $event
 642          * @return array
 643          * @since 1.26
 644          */
 645         public function modifySimpleRelayEvent( array $event ) {
 646                 return $event;
 647         }
 648
 649         /**
 650          * @param string $text
 651          */
 652         protected function debug( $text ) {
 653                 if ( $this->debugMode ) {
 654                         $this->logger->debug( "{class} debug: $text", [
 655                                 'class' => get_class( $this ),
 656                         ] );
 657                 }
 658         }
 659
 660         /**
 661          * Convert an optionally relative time to an absolute time
 662          * @param int $exptime
 663          * @return int
 664          */
 665         protected function convertExpiry( $exptime ) {
 666                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 667                         return time() + $exptime;
 668                 } else {
 669                         return $exptime;
 670                 }
 671         }
 672
 673         /**
 674          * Convert an optionally absolute expiry time to a relative time. If an
 675          * absolute time is specified which is in the past, use a short expiry time.
 676          *
 677          * @param int $exptime
 678          * @return int
 679          */
 680         protected function convertToRelative( $exptime ) {
 681                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 682                         $exptime -= time();
 683                         if ( $exptime <= 0 ) {
 684                                 $exptime = 1;
 685                         }
 686                         return $exptime;
 687                 } else {
 688                         return $exptime;
 689                 }
 690         }
 691
 692         /**
 693          * Check if a value is an integer
 694          *
 695          * @param mixed $value
 696          * @return bool
 697          */
 698         protected function isInteger( $value ) {
 699                 return ( is_int( $value ) || ctype_digit( $value ) );
 700         }
 701
 702         /**
 703          * Construct a cache key.
 704          *
 705          * @since 1.27
 706          * @param string $keyspace
 707          * @param array $args
 708          * @return string
 709          */
 710         public function makeKeyInternal( $keyspace, $args ) {
 711                 $key = $keyspace;
 712                 foreach ( $args as $arg ) {
 713                         $arg = str_replace( ':', '%3A', $arg );
 714                         $key = $key . ':' . $arg;
 715                 }
 716                 return strtr( $key, ' ', '_' );
 717         }
 718
 719         /**
 720          * Make a global cache key.
 721          *
 722          * @since 1.27
 723          * @param string ... Key component (variadic)
 724          * @return string
 725          */
 726         public function makeGlobalKey() {
 727                 return $this->makeKeyInternal( 'global', func_get_args() );
 728         }
 729
 730         /**
 731          * Make a cache key, scoped to this instance's keyspace.
 732          *
 733          * @since 1.27
 734          * @param string ... Key component (variadic)
 735          * @return string
 736          */
 737         public function makeKey() {
 738                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 739         }
 740
 741         /**
 742          * @param integer $flag ATTR_* class constant
 743          * @return integer QOS_* class constant
 744          * @since 1.28
 745          */
 746         public function getQoS( $flag ) {
 747                 return isset( $this->attrMap[$flag] ) ? $this->attrMap[$flag] : self::QOS_UNKNOWN;
 748         }
 749
 750         /**
 751          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 752          *
 753          * @param BagOStuff[] $bags
 754          * @return integer[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 755          */
 756         protected function mergeFlagMaps( array $bags ) {
 757                 $map = [];
 758                 foreach ( $bags as $bag ) {
 759                         foreach ( $bag->attrMap as $attr => $rank ) {
 760                                 if ( isset( $map[$attr] ) ) {
 761                                         $map[$attr] = min( $map[$attr], $rank );
 762                                 } else {
 763                                         $map[$attr] = $rank;
 764                                 }
 765                         }
 766                 }
 767
 768                 return $map;
 769         }
 770 }