includes/libs/objectcache/BagOStuff.php

   1 <?php
   2 /**
   3  * Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
   4  * https://www.mediawiki.org/
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License along
  17  * with this program; if not, write to the Free Software Foundation, Inc.,
  18  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  19  * http://www.gnu.org/copyleft/gpl.html
  20  *
  21  * @file
  22  * @ingroup Cache
  23  */
  24
  25 /**
  26  * @defgroup Cache Cache
  27  */
  28
  29 use Psr\Log\LoggerAwareInterface;
  30 use Psr\Log\LoggerInterface;
  31 use Psr\Log\NullLogger;
  32 use Wikimedia\ScopedCallback;
  33 use Wikimedia\WaitConditionLoop;
  34
  35 /**
  36  * Class representing a cache/ephemeral data store
  37  *
  38  * This interface is intended to be more or less compatible with the PHP memcached client.
  39  *
  40  * Instances of this class should be created with an intended access scope, such as:
  41  *   - a) A single PHP thread on a server (e.g. stored in a PHP variable)
  42  *   - b) A single application server (e.g. stored in APC or sqlite)
  43  *   - c) All application servers in datacenter (e.g. stored in memcached or mysql)
  44  *   - d) All application servers in all datacenters (e.g. stored via mcrouter or dynomite)
  45  *
  46  * Callers should use the proper factory methods that yield BagOStuff instances. Site admins
  47  * should make sure the configuration for those factory methods matches their access scope.
  48  * BagOStuff subclasses have widely varying levels of support for replication features.
  49  *
  50  * For any given instance, methods like lock(), unlock(), merge(), and set() with WRITE_SYNC
  51  * should semantically operate over its entire access scope; any nodes/threads in that scope
  52  * should serialize appropriately when using them. Likewise, a call to get() with READ_LATEST
  53  * from one node in its access scope should reflect the prior changes of any other node its access
  54  * scope. Any get() should reflect the changes of any prior set() with WRITE_SYNC.
  55  *
  56  * @ingroup Cache
  57  */
  58 abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
  59         /** @var array[] Lock tracking */
  60         protected $locks = [];
  61         /** @var int ERR_* class constant */
  62         protected $lastError = self::ERR_NONE;
  63         /** @var string */
  64         protected $keyspace = 'local';
  65         /** @var LoggerInterface */
  66         protected $logger;
  67         /** @var callable|null */
  68         protected $asyncHandler;
  69         /** @var int Seconds */
  70         protected $syncTimeout;
  71
  72         /** @var bool */
  73         private $debugMode = false;
  74         /** @var array */
  75         private $duplicateKeyLookups = [];
  76         /** @var bool */
  77         private $reportDupes = false;
  78         /** @var bool */
  79         private $dupeTrackScheduled = false;
  80
  81         /** @var callable[] */
  82         protected $busyCallbacks = [];
  83
  84         /** @var float|null */
  85         private $wallClockOverride;
  86
  87         /** @var int[] Map of (ATTR_* class constant => QOS_* class constant) */
  88         protected $attrMap = [];
  89
  90         /** Bitfield constants for get()/getMulti() */
  91         const READ_LATEST = 1; // use latest data for replicated stores
  92         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  93         /** Bitfield constants for set()/merge() */
  94         const WRITE_SYNC = 4; // synchronously write to all locations for replicated stores
  95         const WRITE_CACHE_ONLY = 8; // Only change state of the in-memory cache
  96
  97         /**
  98          * $params include:
  99          *   - logger: Psr\Log\LoggerInterface instance
 100          *   - keyspace: Default keyspace for $this->makeKey()
 101          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
 102          *      In CLI mode, it should run the task immediately.
 103          *   - reportDupes: Whether to emit warning log messages for all keys that were
 104          *      requested more than once (requires an asyncHandler).
 105          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
 106          * @param array $params
 107          */
 108         public function __construct( array $params = [] ) {
 109                 $this->setLogger( $params['logger'] ?? new NullLogger() );
 110
 111                 if ( isset( $params['keyspace'] ) ) {
 112                         $this->keyspace = $params['keyspace'];
 113                 }
 114
 115                 $this->asyncHandler = $params['asyncHandler'] ?? null;
 116
 117                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 118                         $this->reportDupes = true;
 119                 }
 120
 121                 $this->syncTimeout = $params['syncTimeout'] ?? 3;
 122         }
 123
 124         /**
 125          * @param LoggerInterface $logger
 126          * @return void
 127          */
 128         public function setLogger( LoggerInterface $logger ) {
 129                 $this->logger = $logger;
 130         }
 131
 132         /**
 133          * @param bool $bool
 134          */
 135         public function setDebug( $bool ) {
 136                 $this->debugMode = $bool;
 137         }
 138
 139         /**
 140          * Get an item with the given key, regenerating and setting it if not found
 141          *
 142          * Nothing is stored nor deleted if the callback returns false
 143          *
 144          * @param string $key
 145          * @param int $ttl Time-to-live (seconds)
 146          * @param callable $callback Callback that derives the new value
 147          * @param int $flags Bitfield of BagOStuff::READ_* or BagOStuff::WRITE_* constants [optional]
 148          * @return mixed The cached value if found or the result of $callback otherwise
 149          * @since 1.27
 150          */
 151         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 152                 $value = $this->get( $key, $flags );
 153
 154                 if ( $value === false ) {
 155                         if ( !is_callable( $callback ) ) {
 156                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 157                         }
 158                         $value = call_user_func( $callback );
 159                         if ( $value !== false ) {
 160                                 $this->set( $key, $value, $ttl, $flags );
 161                         }
 162                 }
 163
 164                 return $value;
 165         }
 166
 167         /**
 168          * Get an item with the given key
 169          *
 170          * If the key includes a deterministic input hash (e.g. the key can only have
 171          * the correct value) or complete staleness checks are handled by the caller
 172          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 173          * This lets tiered backends know they can safely upgrade a cached value to
 174          * higher tiers using standard TTLs.
 175          *
 176          * @param string $key
 177          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 178          * @param int|null $oldFlags [unused]
 179          * @return mixed Returns false on failure or if the item does not exist
 180          */
 181         public function get( $key, $flags = 0, $oldFlags = null ) {
 182                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 183                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 184
 185                 $this->trackDuplicateKeys( $key );
 186
 187                 return $this->doGet( $key, $flags );
 188         }
 189
 190         /**
 191          * Track the number of times that a given key has been used.
 192          * @param string $key
 193          */
 194         private function trackDuplicateKeys( $key ) {
 195                 if ( !$this->reportDupes ) {
 196                         return;
 197                 }
 198
 199                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 200                         // Track that we have seen this key. This N-1 counting style allows
 201                         // easy filtering with array_filter() later.
 202                         $this->duplicateKeyLookups[$key] = 0;
 203                 } else {
 204                         $this->duplicateKeyLookups[$key] += 1;
 205
 206                         if ( $this->dupeTrackScheduled === false ) {
 207                                 $this->dupeTrackScheduled = true;
 208                                 // Schedule a callback that logs keys processed more than once by get().
 209                                 call_user_func( $this->asyncHandler, function () {
 210                                         $dups = array_filter( $this->duplicateKeyLookups );
 211                                         foreach ( $dups as $key => $count ) {
 212                                                 $this->logger->warning(
 213                                                         'Duplicate get(): "{key}" fetched {count} times',
 214                                                         // Count is N-1 of the actual lookup count
 215                                                         [ 'key' => $key, 'count' => $count + 1, ]
 216                                                 );
 217                                         }
 218                                 } );
 219                         }
 220                 }
 221         }
 222
 223         /**
 224          * @param string $key
 225          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 226          * @return mixed Returns false on failure or if the item does not exist
 227          */
 228         abstract protected function doGet( $key, $flags = 0 );
 229
 230         /**
 231          * @note This method is only needed if merge() uses mergeViaCas()
 232          *
 233          * @param string $key
 234          * @param mixed &$casToken
 235          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 236          * @return mixed Returns false on failure or if the item does not exist
 237          * @throws Exception
 238          */
 239         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 240                 throw new Exception( __METHOD__ . ' not implemented.' );
 241         }
 242
 243         /**
 244          * Set an item
 245          *
 246          * @param string $key
 247          * @param mixed $value
 248          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 249          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 250          * @return bool Success
 251          */
 252         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 253
 254         /**
 255          * Delete an item
 256          *
 257          * @param string $key
 258          * @return bool True if the item was deleted or not found, false on failure
 259          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 260          */
 261         abstract public function delete( $key, $flags = 0 );
 262
 263         /**
 264          * Merge changes into the existing cache value (possibly creating a new one)
 265          *
 266          * The callback function returns the new value given the current value
 267          * (which will be false if not present), and takes the arguments:
 268          * (this BagOStuff, cache key, current value, TTL).
 269          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 270          * Nothing is stored nor deleted if the callback returns false.
 271          *
 272          * @param string $key
 273          * @param callable $callback Callback method to be executed
 274          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 275          * @param int $attempts The amount of times to attempt a merge in case of failure
 276          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 277          * @return bool Success
 278          * @throws InvalidArgumentException
 279          */
 280         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 281                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 282         }
 283
 284         /**
 285          * @see BagOStuff::merge()
 286          *
 287          * @param string $key
 288          * @param callable $callback Callback method to be executed
 289          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 290          * @param int $attempts The amount of times to attempt a merge in case of failure
 291          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 292          * @return bool Success
 293          */
 294         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 295                 do {
 296                         $this->clearLastError();
 297                         $reportDupes = $this->reportDupes;
 298                         $this->reportDupes = false;
 299                         $casToken = null; // passed by reference
 300                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 301                         $this->reportDupes = $reportDupes;
 302
 303                         if ( $this->getLastError() ) {
 304                                 $this->logger->warning(
 305                                         __METHOD__ . ' failed due to I/O error on get() for {key}.',
 306                                         [ 'key' => $key ]
 307                                 );
 308
 309                                 return false; // don't spam retries (retry only on races)
 310                         }
 311
 312                         // Derive the new value from the old value
 313                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 314
 315                         $this->clearLastError();
 316                         if ( $value === false ) {
 317                                 $success = true; // do nothing
 318                         } elseif ( $currentValue === false ) {
 319                                 // Try to create the key, failing if it gets created in the meantime
 320                                 $success = $this->add( $key, $value, $exptime, $flags );
 321                         } else {
 322                                 // Try to update the key, failing if it gets changed in the meantime
 323                                 $success = $this->cas( $casToken, $key, $value, $exptime, $flags );
 324                         }
 325                         if ( $this->getLastError() ) {
 326                                 $this->logger->warning(
 327                                         __METHOD__ . ' failed due to I/O error for {key}.',
 328                                         [ 'key' => $key ]
 329                                 );
 330
 331                                 return false; // IO error; don't spam retries
 332                         }
 333                 } while ( !$success && --$attempts );
 334
 335                 return $success;
 336         }
 337
 338         /**
 339          * Check and set an item
 340          *
 341          * @param mixed $casToken
 342          * @param string $key
 343          * @param mixed $value
 344          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 345          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 346          * @return bool Success
 347          * @throws Exception
 348          */
 349         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 350                 if ( !$this->lock( $key, 0 ) ) {
 351                         return false; // non-blocking
 352                 }
 353
 354                 $curCasToken = null; // passed by reference
 355                 $this->getWithToken( $key, $curCasToken, self::READ_LATEST );
 356                 if ( $casToken === $curCasToken ) {
 357                         $success = $this->set( $key, $value, $exptime, $flags );
 358                 } else {
 359                         $this->logger->info(
 360                                 __METHOD__ . ' failed due to race condition for {key}.',
 361                                 [ 'key' => $key ]
 362                         );
 363
 364                         $success = false; // mismatched or failed
 365                 }
 366
 367                 $this->unlock( $key );
 368
 369                 return $success;
 370         }
 371
 372         /**
 373          * @see BagOStuff::merge()
 374          *
 375          * @param string $key
 376          * @param callable $callback Callback method to be executed
 377          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 378          * @param int $attempts The amount of times to attempt a merge in case of failure
 379          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 380          * @return bool Success
 381          */
 382         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 383                 if ( $attempts <= 1 ) {
 384                         $timeout = 0; // clearly intended to be "non-blocking"
 385                 } else {
 386                         $timeout = 3;
 387                 }
 388
 389                 if ( !$this->lock( $key, $timeout ) ) {
 390                         return false;
 391                 }
 392
 393                 $this->clearLastError();
 394                 $reportDupes = $this->reportDupes;
 395                 $this->reportDupes = false;
 396                 $currentValue = $this->get( $key, self::READ_LATEST );
 397                 $this->reportDupes = $reportDupes;
 398
 399                 if ( $this->getLastError() ) {
 400                         $this->logger->warning(
 401                                 __METHOD__ . ' failed due to I/O error on get() for {key}.',
 402                                 [ 'key' => $key ]
 403                         );
 404
 405                         $success = false;
 406                 } else {
 407                         // Derive the new value from the old value
 408                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 409                         if ( $value === false ) {
 410                                 $success = true; // do nothing
 411                         } else {
 412                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 413                         }
 414                 }
 415
 416                 if ( !$this->unlock( $key ) ) {
 417                         // this should never happen
 418                         trigger_error( "Could not release lock for key '$key'." );
 419                 }
 420
 421                 return $success;
 422         }
 423
 424         /**
 425          * Change the expiration on a key if it exists
 426          *
 427          * If an expiry in the past is given then the key will immediately be expired
 428          *
 429          * @param string $key
 430          * @param int $expiry TTL or UNIX timestamp
 431          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 432          * @return bool Success Returns false on failure or if the item does not exist
 433          * @since 1.28
 434          */
 435         public function changeTTL( $key, $expiry = 0, $flags = 0 ) {
 436                 $found = false;
 437
 438                 $ok = $this->merge(
 439                         $key,
 440                         function ( $cache, $ttl, $currentValue ) use ( &$found ) {
 441                                 $found = ( $currentValue !== false );
 442
 443                                 return $currentValue; // nothing is written if this is false
 444                         },
 445                         $expiry,
 446                         1, // 1 attempt
 447                         $flags
 448                 );
 449
 450                 return ( $ok && $found );
 451         }
 452
 453         /**
 454          * Acquire an advisory lock on a key string
 455          *
 456          * Note that if reentry is enabled, duplicate calls ignore $expiry
 457          *
 458          * @param string $key
 459          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 460          * @param int $expiry Lock expiry [optional]; 1 day maximum
 461          * @param string $rclass Allow reentry if set and the current lock used this value
 462          * @return bool Success
 463          */
 464         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 465                 // Avoid deadlocks and allow lock reentry if specified
 466                 if ( isset( $this->locks[$key] ) ) {
 467                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 468                                 ++$this->locks[$key]['depth'];
 469                                 return true;
 470                         } else {
 471                                 return false;
 472                         }
 473                 }
 474
 475                 $fname = __METHOD__;
 476                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 477                 $loop = new WaitConditionLoop(
 478                         function () use ( $key, $expiry, $fname ) {
 479                                 $this->clearLastError();
 480                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 481                                         return WaitConditionLoop::CONDITION_REACHED; // locked!
 482                                 } elseif ( $this->getLastError() ) {
 483                                         $this->logger->warning(
 484                                                 $fname . ' failed due to I/O error for {key}.',
 485                                                 [ 'key' => $key ]
 486                                         );
 487
 488                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 489                                 }
 490
 491                                 return WaitConditionLoop::CONDITION_CONTINUE;
 492                         },
 493                         $timeout
 494                 );
 495
 496                 $code = $loop->invoke();
 497                 $locked = ( $code === $loop::CONDITION_REACHED );
 498                 if ( $locked ) {
 499                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 500                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 501                         $this->logger->warning(
 502                                 "$fname failed due to timeout for {key}.",
 503                                 [ 'key' => $key, 'timeout' => $timeout ]
 504                         );
 505                 }
 506
 507                 return $locked;
 508         }
 509
 510         /**
 511          * Release an advisory lock on a key string
 512          *
 513          * @param string $key
 514          * @return bool Success
 515          */
 516         public function unlock( $key ) {
 517                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 518                         unset( $this->locks[$key] );
 519
 520                         $ok = $this->delete( "{$key}:lock" );
 521                         if ( !$ok ) {
 522                                 $this->logger->warning(
 523                                         __METHOD__ . ' failed to release lock for {key}.',
 524                                         [ 'key' => $key ]
 525                                 );
 526                         }
 527
 528                         return $ok;
 529                 }
 530
 531                 return true;
 532         }
 533
 534         /**
 535          * Get a lightweight exclusive self-unlocking lock
 536          *
 537          * Note that the same lock cannot be acquired twice.
 538          *
 539          * This is useful for task de-duplication or to avoid obtrusive
 540          * (though non-corrupting) DB errors like INSERT key conflicts
 541          * or deadlocks when using LOCK IN SHARE MODE.
 542          *
 543          * @param string $key
 544          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 545          * @param int $expiry Lock expiry [optional]; 1 day maximum
 546          * @param string $rclass Allow reentry if set and the current lock used this value
 547          * @return ScopedCallback|null Returns null on failure
 548          * @since 1.26
 549          */
 550         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 551                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 552
 553                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 554                         return null;
 555                 }
 556
 557                 $lSince = $this->getCurrentTime(); // lock timestamp
 558
 559                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 560                         $latency = 0.050; // latency skew (err towards keeping lock present)
 561                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 562                         if ( ( $age + $latency ) >= $expiry ) {
 563                                 $this->logger->warning(
 564                                         "Lock for {key} held too long ({age} sec).",
 565                                         [ 'key' => $key, 'age' => $age ]
 566                                 );
 567                                 return; // expired; it's not "safe" to delete the key
 568                         }
 569                         $this->unlock( $key );
 570                 } );
 571         }
 572
 573         /**
 574          * Delete all objects expiring before a certain date.
 575          * @param string $date The reference date in MW format
 576          * @param callable|bool $progressCallback Optional, a function which will be called
 577          *     regularly during long-running operations with the percentage progress
 578          *     as the first parameter.
 579          *
 580          * @return bool Success, false if unimplemented
 581          */
 582         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 583                 // stub
 584                 return false;
 585         }
 586
 587         /**
 588          * Get an associative array containing the item for each of the keys that have items.
 589          * @param string[] $keys List of keys
 590          * @param int $flags Bitfield; supports READ_LATEST [optional]
 591          * @return array
 592          */
 593         public function getMulti( array $keys, $flags = 0 ) {
 594                 $res = [];
 595                 foreach ( $keys as $key ) {
 596                         $val = $this->get( $key, $flags );
 597                         if ( $val !== false ) {
 598                                 $res[$key] = $val;
 599                         }
 600                 }
 601
 602                 return $res;
 603         }
 604
 605         /**
 606          * Batch insertion/replace
 607          * @param mixed[] $data Map of (key => value)
 608          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 609          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 610          * @return bool Success
 611          * @since 1.24
 612          */
 613         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 614                 $res = true;
 615                 foreach ( $data as $key => $value ) {
 616                         if ( !$this->set( $key, $value, $exptime, $flags ) ) {
 617                                 $res = false;
 618                         }
 619                 }
 620
 621                 return $res;
 622         }
 623
 624         /**
 625          * Batch deletion
 626          * @param string[] $keys List of keys
 627          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 628          * @return bool Success
 629          * @since 1.33
 630          */
 631         public function deleteMulti( array $keys, $flags = 0 ) {
 632                 $res = true;
 633                 foreach ( $keys as $key ) {
 634                         $res = $this->delete( $key, $flags ) && $res;
 635                 }
 636
 637                 return $res;
 638         }
 639
 640         /**
 641          * Insertion
 642          * @param string $key
 643          * @param mixed $value
 644          * @param int $exptime
 645          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 646          * @return bool Success
 647          */
 648         abstract public function add( $key, $value, $exptime = 0, $flags = 0 );
 649
 650         /**
 651          * Increase stored value of $key by $value while preserving its TTL
 652          * @param string $key Key to increase
 653          * @param int $value Value to add to $key (default: 1) [optional]
 654          * @return int|bool New value or false on failure
 655          */
 656         abstract public function incr( $key, $value = 1 );
 657
 658         /**
 659          * Decrease stored value of $key by $value while preserving its TTL
 660          * @param string $key
 661          * @param int $value Value to subtract from $key (default: 1) [optional]
 662          * @return int|bool New value or false on failure
 663          */
 664         public function decr( $key, $value = 1 ) {
 665                 return $this->incr( $key, - $value );
 666         }
 667
 668         /**
 669          * Increase stored value of $key by $value while preserving its TTL
 670          *
 671          * This will create the key with value $init and TTL $ttl instead if not present
 672          *
 673          * @param string $key
 674          * @param int $ttl
 675          * @param int $value
 676          * @param int $init
 677          * @return int|bool New value or false on failure
 678          * @since 1.24
 679          */
 680         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 681                 $this->clearLastError();
 682                 $newValue = $this->incr( $key, $value );
 683                 if ( $newValue === false && !$this->getLastError() ) {
 684                         // No key set; initialize
 685                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 686                         if ( $newValue === false && !$this->getLastError() ) {
 687                                 // Raced out initializing; increment
 688                                 $newValue = $this->incr( $key, $value );
 689                         }
 690                 }
 691
 692                 return $newValue;
 693         }
 694
 695         /**
 696          * Get the "last error" registered; clearLastError() should be called manually
 697          * @return int ERR_* constant for the "last error" registry
 698          * @since 1.23
 699          */
 700         public function getLastError() {
 701                 return $this->lastError;
 702         }
 703
 704         /**
 705          * Clear the "last error" registry
 706          * @since 1.23
 707          */
 708         public function clearLastError() {
 709                 $this->lastError = self::ERR_NONE;
 710         }
 711
 712         /**
 713          * Set the "last error" registry
 714          * @param int $err ERR_* constant
 715          * @since 1.23
 716          */
 717         protected function setLastError( $err ) {
 718                 $this->lastError = $err;
 719         }
 720
 721         /**
 722          * Let a callback be run to avoid wasting time on special blocking calls
 723          *
 724          * The callbacks may or may not be called ever, in any particular order.
 725          * They are likely to be invoked when something WRITE_SYNC is used used.
 726          * They should follow a caching pattern as shown below, so that any code
 727          * using the work will get it's result no matter what happens.
 728          * @code
 729          *     $result = null;
 730          *     $workCallback = function () use ( &$result ) {
 731          *         if ( !$result ) {
 732          *             $result = ....
 733          *         }
 734          *         return $result;
 735          *     }
 736          * @endcode
 737          *
 738          * @param callable $workCallback
 739          * @since 1.28
 740          */
 741         public function addBusyCallback( callable $workCallback ) {
 742                 $this->busyCallbacks[] = $workCallback;
 743         }
 744
 745         /**
 746          * @param string $text
 747          */
 748         protected function debug( $text ) {
 749                 if ( $this->debugMode ) {
 750                         $this->logger->debug( "{class} debug: $text", [
 751                                 'class' => static::class,
 752                         ] );
 753                 }
 754         }
 755
 756         /**
 757          * Convert an optionally relative time to an absolute time
 758          * @param int $exptime
 759          * @return int
 760          */
 761         protected function convertExpiry( $exptime ) {
 762                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 763                         return (int)$this->getCurrentTime() + $exptime;
 764                 } else {
 765                         return $exptime;
 766                 }
 767         }
 768
 769         /**
 770          * Convert an optionally absolute expiry time to a relative time. If an
 771          * absolute time is specified which is in the past, use a short expiry time.
 772          *
 773          * @param int $exptime
 774          * @return int
 775          */
 776         protected function convertToRelative( $exptime ) {
 777                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 778                         $exptime -= (int)$this->getCurrentTime();
 779                         if ( $exptime <= 0 ) {
 780                                 $exptime = 1;
 781                         }
 782                         return $exptime;
 783                 } else {
 784                         return $exptime;
 785                 }
 786         }
 787
 788         /**
 789          * Check if a value is an integer
 790          *
 791          * @param mixed $value
 792          * @return bool
 793          */
 794         protected function isInteger( $value ) {
 795                 return ( is_int( $value ) || ctype_digit( $value ) );
 796         }
 797
 798         /**
 799          * Construct a cache key.
 800          *
 801          * @since 1.27
 802          * @param string $keyspace
 803          * @param array $args
 804          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 805          */
 806         public function makeKeyInternal( $keyspace, $args ) {
 807                 $key = $keyspace;
 808                 foreach ( $args as $arg ) {
 809                         $key .= ':' . str_replace( ':', '%3A', $arg );
 810                 }
 811                 return strtr( $key, ' ', '_' );
 812         }
 813
 814         /**
 815          * Make a global cache key.
 816          *
 817          * @since 1.27
 818          * @param string $class Key class
 819          * @param string|null $component [optional] Key component (starting with a key collection name)
 820          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 821          */
 822         public function makeGlobalKey( $class, $component = null ) {
 823                 return $this->makeKeyInternal( 'global', func_get_args() );
 824         }
 825
 826         /**
 827          * Make a cache key, scoped to this instance's keyspace.
 828          *
 829          * @since 1.27
 830          * @param string $class Key class
 831          * @param string|null $component [optional] Key component (starting with a key collection name)
 832          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 833          */
 834         public function makeKey( $class, $component = null ) {
 835                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 836         }
 837
 838         /**
 839          * @param int $flag ATTR_* class constant
 840          * @return int QOS_* class constant
 841          * @since 1.28
 842          */
 843         public function getQoS( $flag ) {
 844                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 845         }
 846
 847         /**
 848          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 849          *
 850          * @param BagOStuff[] $bags
 851          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 852          */
 853         protected function mergeFlagMaps( array $bags ) {
 854                 $map = [];
 855                 foreach ( $bags as $bag ) {
 856                         foreach ( $bag->attrMap as $attr => $rank ) {
 857                                 if ( isset( $map[$attr] ) ) {
 858                                         $map[$attr] = min( $map[$attr], $rank );
 859                                 } else {
 860                                         $map[$attr] = $rank;
 861                                 }
 862                         }
 863                 }
 864
 865                 return $map;
 866         }
 867
 868         /**
 869          * @return float UNIX timestamp
 870          * @codeCoverageIgnore
 871          */
 872         protected function getCurrentTime() {
 873                 return $this->wallClockOverride ?: microtime( true );
 874         }
 875
 876         /**
 877          * @param float|null &$time Mock UNIX timestamp for testing
 878          * @codeCoverageIgnore
 879          */
 880         public function setMockTime( &$time ) {
 881                 $this->wallClockOverride =& $time;
 882         }
 883 }