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 */
  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         /** Possible values for getLastError() */
  74         const ERR_NONE = 0; // no error
  75         const ERR_NO_RESPONSE = 1; // no response
  76         const ERR_UNREACHABLE = 2; // can't connect
  77         const ERR_UNEXPECTED = 3; // response gave some error
  78
  79         /** Bitfield constants for get()/getMulti() */
  80         const READ_LATEST = 1; // use latest data for replicated stores
  81         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  82         /** Bitfield constants for set()/merge() */
  83         const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
  84         const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache
  85
  86         /**
  87          * $params include:
  88          *   - logger: Psr\Log\LoggerInterface instance
  89          *   - keyspace: Default keyspace for $this->makeKey()
  90          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
  91          *      In CLI mode, it should run the task immediately.
  92          *   - reportDupes: Whether to emit warning log messages for all keys that were
  93          *      requested more than once (requires an asyncHandler).
  94          * @param array $params
  95          */
  96         public function __construct( array $params = [] ) {
  97                 if ( isset( $params['logger'] ) ) {
  98                         $this->setLogger( $params['logger'] );
  99                 } else {
 100                         $this->setLogger( new NullLogger() );
 101                 }
 102
 103                 if ( isset( $params['keyspace'] ) ) {
 104                         $this->keyspace = $params['keyspace'];
 105                 }
 106
 107                 $this->asyncHandler = isset( $params['asyncHandler'] )
 108                         ? $params['asyncHandler']
 109                         : null;
 110
 111                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 112                         $this->reportDupes = true;
 113                 }
 114         }
 115
 116         /**
 117          * @param LoggerInterface $logger
 118          * @return null
 119          */
 120         public function setLogger( LoggerInterface $logger ) {
 121                 $this->logger = $logger;
 122         }
 123
 124         /**
 125          * @param bool $bool
 126          */
 127         public function setDebug( $bool ) {
 128                 $this->debugMode = $bool;
 129         }
 130
 131         /**
 132          * Get an item with the given key, regenerating and setting it if not found
 133          *
 134          * If the callback returns false, then nothing is stored.
 135          *
 136          * @param string $key
 137          * @param int $ttl Time-to-live (seconds)
 138          * @param callable $callback Callback that derives the new value
 139          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 140          * @return mixed The cached value if found or the result of $callback otherwise
 141          * @since 1.27
 142          */
 143         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 144                 $value = $this->get( $key, $flags );
 145
 146                 if ( $value === false ) {
 147                         if ( !is_callable( $callback ) ) {
 148                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 149                         }
 150                         $value = call_user_func( $callback );
 151                         if ( $value !== false ) {
 152                                 $this->set( $key, $value, $ttl );
 153                         }
 154                 }
 155
 156                 return $value;
 157         }
 158
 159         /**
 160          * Get an item with the given key
 161          *
 162          * If the key includes a determistic input hash (e.g. the key can only have
 163          * the correct value) or complete staleness checks are handled by the caller
 164          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 165          * This lets tiered backends know they can safely upgrade a cached value to
 166          * higher tiers using standard TTLs.
 167          *
 168          * @param string $key
 169          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 170          * @param integer $oldFlags [unused]
 171          * @return mixed Returns false on failure and if the item does not exist
 172          */
 173         public function get( $key, $flags = 0, $oldFlags = null ) {
 174                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 175                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 176
 177                 $this->trackDuplicateKeys( $key );
 178
 179                 return $this->doGet( $key, $flags );
 180         }
 181
 182         /**
 183          * Track the number of times that a given key has been used.
 184          * @param string $key
 185          */
 186         private function trackDuplicateKeys( $key ) {
 187                 if ( !$this->reportDupes ) {
 188                         return;
 189                 }
 190
 191                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 192                         // Track that we have seen this key. This N-1 counting style allows
 193                         // easy filtering with array_filter() later.
 194                         $this->duplicateKeyLookups[$key] = 0;
 195                 } else {
 196                         $this->duplicateKeyLookups[$key] += 1;
 197
 198                         if ( $this->dupeTrackScheduled === false ) {
 199                                 $this->dupeTrackScheduled = true;
 200                                 // Schedule a callback that logs keys processed more than once by get().
 201                                 call_user_func( $this->asyncHandler, function () {
 202                                         $dups = array_filter( $this->duplicateKeyLookups );
 203                                         foreach ( $dups as $key => $count ) {
 204                                                 $this->logger->warning(
 205                                                         'Duplicate get(): "{key}" fetched {count} times',
 206                                                         // Count is N-1 of the actual lookup count
 207                                                         [ 'key' => $key, 'count' => $count + 1, ]
 208                                                 );
 209                                         }
 210                                 } );
 211                         }
 212                 }
 213         }
 214
 215         /**
 216          * @param string $key
 217          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 218          * @return mixed Returns false on failure and if the item does not exist
 219          */
 220         abstract protected function doGet( $key, $flags = 0 );
 221
 222         /**
 223          * @note: This method is only needed if merge() uses mergeViaCas()
 224          *
 225          * @param string $key
 226          * @param mixed $casToken
 227          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 228          * @return mixed Returns false on failure and if the item does not exist
 229          * @throws Exception
 230          */
 231         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 232                 throw new Exception( __METHOD__ . ' not implemented.' );
 233         }
 234
 235         /**
 236          * Set an item
 237          *
 238          * @param string $key
 239          * @param mixed $value
 240          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 241          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 242          * @return bool Success
 243          */
 244         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 245
 246         /**
 247          * Delete an item
 248          *
 249          * @param string $key
 250          * @return bool True if the item was deleted or not found, false on failure
 251          */
 252         abstract public function delete( $key );
 253
 254         /**
 255          * Merge changes into the existing cache value (possibly creating a new one)
 256          *
 257          * The callback function returns the new value given the current value
 258          * (which will be false if not present), and takes the arguments:
 259          * (this BagOStuff, cache key, current value, TTL).
 260          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 261          *
 262          * @param string $key
 263          * @param callable $callback Callback method to be executed
 264          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 265          * @param int $attempts The amount of times to attempt a merge in case of failure
 266          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 267          * @return bool Success
 268          * @throws InvalidArgumentException
 269          */
 270         public function merge( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 271                 if ( !is_callable( $callback ) ) {
 272                         throw new InvalidArgumentException( "Got invalid callback." );
 273                 }
 274
 275                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 276         }
 277
 278         /**
 279          * @see BagOStuff::merge()
 280          *
 281          * @param string $key
 282          * @param callable $callback Callback method to be executed
 283          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 284          * @param int $attempts The amount of times to attempt a merge in case of failure
 285          * @return bool Success
 286          */
 287         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 288                 do {
 289                         $this->clearLastError();
 290                         $reportDupes = $this->reportDupes;
 291                         $this->reportDupes = false;
 292                         $casToken = null; // passed by reference
 293                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 294                         $this->reportDupes = $reportDupes;
 295
 296                         if ( $this->getLastError() ) {
 297                                 return false; // don't spam retries (retry only on races)
 298                         }
 299
 300                         // Derive the new value from the old value
 301                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 302
 303                         $this->clearLastError();
 304                         if ( $value === false ) {
 305                                 $success = true; // do nothing
 306                         } elseif ( $currentValue === false ) {
 307                                 // Try to create the key, failing if it gets created in the meantime
 308                                 $success = $this->add( $key, $value, $exptime );
 309                         } else {
 310                                 // Try to update the key, failing if it gets changed in the meantime
 311                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 312                         }
 313                         if ( $this->getLastError() ) {
 314                                 return false; // IO error; don't spam retries
 315                         }
 316                 } while ( !$success && --$attempts );
 317
 318                 return $success;
 319         }
 320
 321         /**
 322          * Check and set an item
 323          *
 324          * @param mixed $casToken
 325          * @param string $key
 326          * @param mixed $value
 327          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 328          * @return bool Success
 329          * @throws Exception
 330          */
 331         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 332                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 333         }
 334
 335         /**
 336          * @see BagOStuff::merge()
 337          *
 338          * @param string $key
 339          * @param callable $callback Callback method to be executed
 340          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 341          * @param int $attempts The amount of times to attempt a merge in case of failure
 342          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 343          * @return bool Success
 344          */
 345         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 346                 if ( !$this->lock( $key, 6 ) ) {
 347                         return false;
 348                 }
 349
 350                 $this->clearLastError();
 351                 $reportDupes = $this->reportDupes;
 352                 $this->reportDupes = false;
 353                 $currentValue = $this->get( $key, self::READ_LATEST );
 354                 $this->reportDupes = $reportDupes;
 355
 356                 if ( $this->getLastError() ) {
 357                         $success = false;
 358                 } else {
 359                         // Derive the new value from the old value
 360                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 361                         if ( $value === false ) {
 362                                 $success = true; // do nothing
 363                         } else {
 364                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 365                         }
 366                 }
 367
 368                 if ( !$this->unlock( $key ) ) {
 369                         // this should never happen
 370                         trigger_error( "Could not release lock for key '$key'." );
 371                 }
 372
 373                 return $success;
 374         }
 375
 376         /**
 377          * Acquire an advisory lock on a key string
 378          *
 379          * Note that if reentry is enabled, duplicate calls ignore $expiry
 380          *
 381          * @param string $key
 382          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 383          * @param int $expiry Lock expiry [optional]; 1 day maximum
 384          * @param string $rclass Allow reentry if set and the current lock used this value
 385          * @return bool Success
 386          */
 387         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 388                 // Avoid deadlocks and allow lock reentry if specified
 389                 if ( isset( $this->locks[$key] ) ) {
 390                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 391                                 ++$this->locks[$key]['depth'];
 392                                 return true;
 393                         } else {
 394                                 return false;
 395                         }
 396                 }
 397
 398                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 399
 400                 $this->clearLastError();
 401                 $timestamp = microtime( true ); // starting UNIX timestamp
 402                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 403                         $locked = true;
 404                 } elseif ( $this->getLastError() || $timeout <= 0 ) {
 405                         $locked = false; // network partition or non-blocking
 406                 } else {
 407                         // Estimate the RTT (us); use 1ms minimum for sanity
 408                         $uRTT = max( 1e3, ceil( 1e6 * ( microtime( true ) - $timestamp ) ) );
 409                         $sleep = 2 * $uRTT; // rough time to do get()+set()
 410
 411                         $attempts = 0; // failed attempts
 412                         do {
 413                                 if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
 414                                         // Exponentially back off after failed attempts to avoid network spam.
 415                                         // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 416                                         $sleep *= 2;
 417                                 }
 418                                 usleep( $sleep ); // back off
 419                                 $this->clearLastError();
 420                                 $locked = $this->add( "{$key}:lock", 1, $expiry );
 421                                 if ( $this->getLastError() ) {
 422                                         $locked = false; // network partition
 423                                         break;
 424                                 }
 425                         } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 426                 }
 427
 428                 if ( $locked ) {
 429                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 430                 }
 431
 432                 return $locked;
 433         }
 434
 435         /**
 436          * Release an advisory lock on a key string
 437          *
 438          * @param string $key
 439          * @return bool Success
 440          */
 441         public function unlock( $key ) {
 442                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 443                         unset( $this->locks[$key] );
 444
 445                         return $this->delete( "{$key}:lock" );
 446                 }
 447
 448                 return true;
 449         }
 450
 451         /**
 452          * Get a lightweight exclusive self-unlocking lock
 453          *
 454          * Note that the same lock cannot be acquired twice.
 455          *
 456          * This is useful for task de-duplication or to avoid obtrusive
 457          * (though non-corrupting) DB errors like INSERT key conflicts
 458          * or deadlocks when using LOCK IN SHARE MODE.
 459          *
 460          * @param string $key
 461          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 462          * @param int $expiry Lock expiry [optional]; 1 day maximum
 463          * @param string $rclass Allow reentry if set and the current lock used this value
 464          * @return ScopedCallback|null Returns null on failure
 465          * @since 1.26
 466          */
 467         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 468                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 469
 470                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 471                         return null;
 472                 }
 473
 474                 $lSince = microtime( true ); // lock timestamp
 475
 476                 return new ScopedCallback( function() use ( $key, $lSince, $expiry ) {
 477                         $latency = .050; // latency skew (err towards keeping lock present)
 478                         $age = ( microtime( true ) - $lSince + $latency );
 479                         if ( ( $age + $latency ) >= $expiry ) {
 480                                 $this->logger->warning( "Lock for $key held too long ($age sec)." );
 481                                 return; // expired; it's not "safe" to delete the key
 482                         }
 483                         $this->unlock( $key );
 484                 } );
 485         }
 486
 487         /**
 488          * Delete all objects expiring before a certain date.
 489          * @param string $date The reference date in MW format
 490          * @param callable|bool $progressCallback Optional, a function which will be called
 491          *     regularly during long-running operations with the percentage progress
 492          *     as the first parameter.
 493          *
 494          * @return bool Success, false if unimplemented
 495          */
 496         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 497                 // stub
 498                 return false;
 499         }
 500
 501         /**
 502          * Get an associative array containing the item for each of the keys that have items.
 503          * @param array $keys List of strings
 504          * @param integer $flags Bitfield; supports READ_LATEST [optional]
 505          * @return array
 506          */
 507         public function getMulti( array $keys, $flags = 0 ) {
 508                 $res = [];
 509                 foreach ( $keys as $key ) {
 510                         $val = $this->get( $key );
 511                         if ( $val !== false ) {
 512                                 $res[$key] = $val;
 513                         }
 514                 }
 515                 return $res;
 516         }
 517
 518         /**
 519          * Batch insertion
 520          * @param array $data $key => $value assoc array
 521          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 522          * @return bool Success
 523          * @since 1.24
 524          */
 525         public function setMulti( array $data, $exptime = 0 ) {
 526                 $res = true;
 527                 foreach ( $data as $key => $value ) {
 528                         if ( !$this->set( $key, $value, $exptime ) ) {
 529                                 $res = false;
 530                         }
 531                 }
 532                 return $res;
 533         }
 534
 535         /**
 536          * @param string $key
 537          * @param mixed $value
 538          * @param int $exptime
 539          * @return bool Success
 540          */
 541         public function add( $key, $value, $exptime = 0 ) {
 542                 if ( $this->get( $key ) === false ) {
 543                         return $this->set( $key, $value, $exptime );
 544                 }
 545                 return false; // key already set
 546         }
 547
 548         /**
 549          * Increase stored value of $key by $value while preserving its TTL
 550          * @param string $key Key to increase
 551          * @param int $value Value to add to $key (Default 1)
 552          * @return int|bool New value or false on failure
 553          */
 554         public function incr( $key, $value = 1 ) {
 555                 if ( !$this->lock( $key ) ) {
 556                         return false;
 557                 }
 558                 $n = $this->get( $key );
 559                 if ( $this->isInteger( $n ) ) { // key exists?
 560                         $n += intval( $value );
 561                         $this->set( $key, max( 0, $n ) ); // exptime?
 562                 } else {
 563                         $n = false;
 564                 }
 565                 $this->unlock( $key );
 566
 567                 return $n;
 568         }
 569
 570         /**
 571          * Decrease stored value of $key by $value while preserving its TTL
 572          * @param string $key
 573          * @param int $value
 574          * @return int|bool New value or false on failure
 575          */
 576         public function decr( $key, $value = 1 ) {
 577                 return $this->incr( $key, - $value );
 578         }
 579
 580         /**
 581          * Increase stored value of $key by $value while preserving its TTL
 582          *
 583          * This will create the key with value $init and TTL $ttl instead if not present
 584          *
 585          * @param string $key
 586          * @param int $ttl
 587          * @param int $value
 588          * @param int $init
 589          * @return int|bool New value or false on failure
 590          * @since 1.24
 591          */
 592         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 593                 $newValue = $this->incr( $key, $value );
 594                 if ( $newValue === false ) {
 595                         // No key set; initialize
 596                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 597                 }
 598                 if ( $newValue === false ) {
 599                         // Raced out initializing; increment
 600                         $newValue = $this->incr( $key, $value );
 601                 }
 602
 603                 return $newValue;
 604         }
 605
 606         /**
 607          * Get the "last error" registered; clearLastError() should be called manually
 608          * @return int ERR_* constant for the "last error" registry
 609          * @since 1.23
 610          */
 611         public function getLastError() {
 612                 return $this->lastError;
 613         }
 614
 615         /**
 616          * Clear the "last error" registry
 617          * @since 1.23
 618          */
 619         public function clearLastError() {
 620                 $this->lastError = self::ERR_NONE;
 621         }
 622
 623         /**
 624          * Set the "last error" registry
 625          * @param int $err ERR_* constant
 626          * @since 1.23
 627          */
 628         protected function setLastError( $err ) {
 629                 $this->lastError = $err;
 630         }
 631
 632         /**
 633          * Modify a cache update operation array for EventRelayer::notify()
 634          *
 635          * This is used for relayed writes, e.g. for broadcasting a change
 636          * to multiple data-centers. If the array contains a 'val' field
 637          * then the command involves setting a key to that value. Note that
 638          * for simplicity, 'val' is always a simple scalar value. This method
 639          * is used to possibly serialize the value and add any cache-specific
 640          * key/values needed for the relayer daemon (e.g. memcached flags).
 641          *
 642          * @param array $event
 643          * @return array
 644          * @since 1.26
 645          */
 646         public function modifySimpleRelayEvent( array $event ) {
 647                 return $event;
 648         }
 649
 650         /**
 651          * @param string $text
 652          */
 653         protected function debug( $text ) {
 654                 if ( $this->debugMode ) {
 655                         $this->logger->debug( "{class} debug: $text", [
 656                                 'class' => get_class( $this ),
 657                         ] );
 658                 }
 659         }
 660
 661         /**
 662          * Convert an optionally relative time to an absolute time
 663          * @param int $exptime
 664          * @return int
 665          */
 666         protected function convertExpiry( $exptime ) {
 667                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 668                         return time() + $exptime;
 669                 } else {
 670                         return $exptime;
 671                 }
 672         }
 673
 674         /**
 675          * Convert an optionally absolute expiry time to a relative time. If an
 676          * absolute time is specified which is in the past, use a short expiry time.
 677          *
 678          * @param int $exptime
 679          * @return int
 680          */
 681         protected function convertToRelative( $exptime ) {
 682                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 683                         $exptime -= time();
 684                         if ( $exptime <= 0 ) {
 685                                 $exptime = 1;
 686                         }
 687                         return $exptime;
 688                 } else {
 689                         return $exptime;
 690                 }
 691         }
 692
 693         /**
 694          * Check if a value is an integer
 695          *
 696          * @param mixed $value
 697          * @return bool
 698          */
 699         protected function isInteger( $value ) {
 700                 return ( is_int( $value ) || ctype_digit( $value ) );
 701         }
 702
 703         /**
 704          * Construct a cache key.
 705          *
 706          * @since 1.27
 707          * @param string $keyspace
 708          * @param array $args
 709          * @return string
 710          */
 711         public function makeKeyInternal( $keyspace, $args ) {
 712                 $key = $keyspace;
 713                 foreach ( $args as $arg ) {
 714                         $arg = str_replace( ':', '%3A', $arg );
 715                         $key = $key . ':' . $arg;
 716                 }
 717                 return strtr( $key, ' ', '_' );
 718         }
 719
 720         /**
 721          * Make a global cache key.
 722          *
 723          * @since 1.27
 724          * @param string ... Key component (variadic)
 725          * @return string
 726          */
 727         public function makeGlobalKey() {
 728                 return $this->makeKeyInternal( 'global', func_get_args() );
 729         }
 730
 731         /**
 732          * Make a cache key, scoped to this instance's keyspace.
 733          *
 734          * @since 1.27
 735          * @param string ... Key component (variadic)
 736          * @return string
 737          */
 738         public function makeKey() {
 739                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 740         }
 741 }