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         /** Possible values for getLastError() */
  91         const ERR_NONE = 0; // no error
  92         const ERR_NO_RESPONSE = 1; // no response
  93         const ERR_UNREACHABLE = 2; // can't connect
  94         const ERR_UNEXPECTED = 3; // response gave some error
  95
  96         /** Bitfield constants for get()/getMulti() */
  97         const READ_LATEST = 1; // use latest data for replicated stores
  98         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  99         /** Bitfield constants for set()/merge() */
 100         const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
 101         const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache
 102
 103         /**
 104          * $params include:
 105          *   - logger: Psr\Log\LoggerInterface instance
 106          *   - keyspace: Default keyspace for $this->makeKey()
 107          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
 108          *      In CLI mode, it should run the task immediately.
 109          *   - reportDupes: Whether to emit warning log messages for all keys that were
 110          *      requested more than once (requires an asyncHandler).
 111          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
 112          * @param array $params
 113          */
 114         public function __construct( array $params = [] ) {
 115                 $this->setLogger( $params['logger'] ?? new NullLogger() );
 116
 117                 if ( isset( $params['keyspace'] ) ) {
 118                         $this->keyspace = $params['keyspace'];
 119                 }
 120
 121                 $this->asyncHandler = $params['asyncHandler'] ?? null;
 122
 123                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 124                         $this->reportDupes = true;
 125                 }
 126
 127                 $this->syncTimeout = $params['syncTimeout'] ?? 3;
 128         }
 129
 130         /**
 131          * @param LoggerInterface $logger
 132          * @return void
 133          */
 134         public function setLogger( LoggerInterface $logger ) {
 135                 $this->logger = $logger;
 136         }
 137
 138         /**
 139          * @param bool $bool
 140          */
 141         public function setDebug( $bool ) {
 142                 $this->debugMode = $bool;
 143         }
 144
 145         /**
 146          * Get an item with the given key, regenerating and setting it if not found
 147          *
 148          * If the callback returns false, then nothing is stored.
 149          *
 150          * @param string $key
 151          * @param int $ttl Time-to-live (seconds)
 152          * @param callable $callback Callback that derives the new value
 153          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 154          * @return mixed The cached value if found or the result of $callback otherwise
 155          * @since 1.27
 156          */
 157         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 158                 $value = $this->get( $key, $flags );
 159
 160                 if ( $value === false ) {
 161                         if ( !is_callable( $callback ) ) {
 162                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 163                         }
 164                         $value = call_user_func( $callback );
 165                         if ( $value !== false ) {
 166                                 $this->set( $key, $value, $ttl );
 167                         }
 168                 }
 169
 170                 return $value;
 171         }
 172
 173         /**
 174          * Get an item with the given key
 175          *
 176          * If the key includes a deterministic input hash (e.g. the key can only have
 177          * the correct value) or complete staleness checks are handled by the caller
 178          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 179          * This lets tiered backends know they can safely upgrade a cached value to
 180          * higher tiers using standard TTLs.
 181          *
 182          * @param string $key
 183          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 184          * @param int|null $oldFlags [unused]
 185          * @return mixed Returns false on failure and if the item does not exist
 186          */
 187         public function get( $key, $flags = 0, $oldFlags = null ) {
 188                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 189                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 190
 191                 $this->trackDuplicateKeys( $key );
 192
 193                 return $this->doGet( $key, $flags );
 194         }
 195
 196         /**
 197          * Track the number of times that a given key has been used.
 198          * @param string $key
 199          */
 200         private function trackDuplicateKeys( $key ) {
 201                 if ( !$this->reportDupes ) {
 202                         return;
 203                 }
 204
 205                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 206                         // Track that we have seen this key. This N-1 counting style allows
 207                         // easy filtering with array_filter() later.
 208                         $this->duplicateKeyLookups[$key] = 0;
 209                 } else {
 210                         $this->duplicateKeyLookups[$key] += 1;
 211
 212                         if ( $this->dupeTrackScheduled === false ) {
 213                                 $this->dupeTrackScheduled = true;
 214                                 // Schedule a callback that logs keys processed more than once by get().
 215                                 call_user_func( $this->asyncHandler, function () {
 216                                         $dups = array_filter( $this->duplicateKeyLookups );
 217                                         foreach ( $dups as $key => $count ) {
 218                                                 $this->logger->warning(
 219                                                         'Duplicate get(): "{key}" fetched {count} times',
 220                                                         // Count is N-1 of the actual lookup count
 221                                                         [ 'key' => $key, 'count' => $count + 1, ]
 222                                                 );
 223                                         }
 224                                 } );
 225                         }
 226                 }
 227         }
 228
 229         /**
 230          * @param string $key
 231          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 232          * @return mixed Returns false on failure and if the item does not exist
 233          */
 234         abstract protected function doGet( $key, $flags = 0 );
 235
 236         /**
 237          * @note This method is only needed if merge() uses mergeViaCas()
 238          *
 239          * @param string $key
 240          * @param mixed &$casToken
 241          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 242          * @return mixed Returns false on failure and if the item does not exist
 243          * @throws Exception
 244          */
 245         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 246                 throw new Exception( __METHOD__ . ' not implemented.' );
 247         }
 248
 249         /**
 250          * Set an item
 251          *
 252          * @param string $key
 253          * @param mixed $value
 254          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 255          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 256          * @return bool Success
 257          */
 258         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 259
 260         /**
 261          * Delete an item
 262          *
 263          * @param string $key
 264          * @return bool True if the item was deleted or not found, false on failure
 265          */
 266         abstract public function delete( $key );
 267
 268         /**
 269          * Merge changes into the existing cache value (possibly creating a new one)
 270          *
 271          * The callback function returns the new value given the current value
 272          * (which will be false if not present), and takes the arguments:
 273          * (this BagOStuff, cache key, current value, TTL).
 274          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 275          *
 276          * @param string $key
 277          * @param callable $callback Callback method to be executed
 278          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 279          * @param int $attempts The amount of times to attempt a merge in case of failure
 280          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 281          * @return bool Success
 282          * @throws InvalidArgumentException
 283          */
 284         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 285                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 286         }
 287
 288         /**
 289          * @see BagOStuff::merge()
 290          *
 291          * @param string $key
 292          * @param callable $callback Callback method to be executed
 293          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 294          * @param int $attempts The amount of times to attempt a merge in case of failure
 295          * @return bool Success
 296          */
 297         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 298                 do {
 299                         $this->clearLastError();
 300                         $reportDupes = $this->reportDupes;
 301                         $this->reportDupes = false;
 302                         $casToken = null; // passed by reference
 303                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 304                         $this->reportDupes = $reportDupes;
 305
 306                         if ( $this->getLastError() ) {
 307                                 $this->logger->warning(
 308                                         __METHOD__ . ' failed due to I/O error on get() for {key}.',
 309                                         [ 'key' => $key ]
 310                                 );
 311
 312                                 return false; // don't spam retries (retry only on races)
 313                         }
 314
 315                         // Derive the new value from the old value
 316                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 317
 318                         $this->clearLastError();
 319                         if ( $value === false ) {
 320                                 $success = true; // do nothing
 321                         } elseif ( $currentValue === false ) {
 322                                 // Try to create the key, failing if it gets created in the meantime
 323                                 $success = $this->add( $key, $value, $exptime );
 324                         } else {
 325                                 // Try to update the key, failing if it gets changed in the meantime
 326                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 327                         }
 328                         if ( $this->getLastError() ) {
 329                                 $this->logger->warning(
 330                                         __METHOD__ . ' failed due to I/O error for {key}.',
 331                                         [ 'key' => $key ]
 332                                 );
 333
 334                                 return false; // IO error; don't spam retries
 335                         }
 336                 } while ( !$success && --$attempts );
 337
 338                 return $success;
 339         }
 340
 341         /**
 342          * Check and set an item
 343          *
 344          * @param mixed $casToken
 345          * @param string $key
 346          * @param mixed $value
 347          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 348          * @return bool Success
 349          * @throws Exception
 350          */
 351         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 352                 if ( !$this->lock( $key, 0 ) ) {
 353                         return false; // non-blocking
 354                 }
 355
 356                 $curCasToken = null; // passed by reference
 357                 $this->getWithToken( $key, $curCasToken, self::READ_LATEST );
 358                 if ( $casToken === $curCasToken ) {
 359                         $success = $this->set( $key, $value, $exptime );
 360                 } else {
 361                         $this->logger->info(
 362                                 __METHOD__ . ' failed due to race condition for {key}.',
 363                                 [ 'key' => $key ]
 364                         );
 365
 366                         $success = false; // mismatched or failed
 367                 }
 368
 369                 $this->unlock( $key );
 370
 371                 return $success;
 372         }
 373
 374         /**
 375          * @see BagOStuff::merge()
 376          *
 377          * @param string $key
 378          * @param callable $callback Callback method to be executed
 379          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 380          * @param int $attempts The amount of times to attempt a merge in case of failure
 381          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 382          * @return bool Success
 383          */
 384         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 385                 if ( $attempts <= 1 ) {
 386                         $timeout = 0; // clearly intended to be "non-blocking"
 387                 } else {
 388                         $timeout = 3;
 389                 }
 390
 391                 if ( !$this->lock( $key, $timeout ) ) {
 392                         return false;
 393                 }
 394
 395                 $this->clearLastError();
 396                 $reportDupes = $this->reportDupes;
 397                 $this->reportDupes = false;
 398                 $currentValue = $this->get( $key, self::READ_LATEST );
 399                 $this->reportDupes = $reportDupes;
 400
 401                 if ( $this->getLastError() ) {
 402                         $this->logger->warning(
 403                                 __METHOD__ . ' failed due to I/O error on get() for {key}.',
 404                                 [ 'key' => $key ]
 405                         );
 406
 407                         $success = false;
 408                 } else {
 409                         // Derive the new value from the old value
 410                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 411                         if ( $value === false ) {
 412                                 $success = true; // do nothing
 413                         } else {
 414                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 415                         }
 416                 }
 417
 418                 if ( !$this->unlock( $key ) ) {
 419                         // this should never happen
 420                         trigger_error( "Could not release lock for key '$key'." );
 421                 }
 422
 423                 return $success;
 424         }
 425
 426         /**
 427          * Reset the TTL on a key if it exists
 428          *
 429          * @param string $key
 430          * @param int $expiry
 431          * @return bool Success Returns false if there is no key
 432          * @since 1.28
 433          */
 434         public function changeTTL( $key, $expiry = 0 ) {
 435                 $value = $this->get( $key );
 436
 437                 return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
 438         }
 439
 440         /**
 441          * Acquire an advisory lock on a key string
 442          *
 443          * Note that if reentry is enabled, duplicate calls ignore $expiry
 444          *
 445          * @param string $key
 446          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 447          * @param int $expiry Lock expiry [optional]; 1 day maximum
 448          * @param string $rclass Allow reentry if set and the current lock used this value
 449          * @return bool Success
 450          */
 451         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 452                 // Avoid deadlocks and allow lock reentry if specified
 453                 if ( isset( $this->locks[$key] ) ) {
 454                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 455                                 ++$this->locks[$key]['depth'];
 456                                 return true;
 457                         } else {
 458                                 return false;
 459                         }
 460                 }
 461
 462                 $fname = __METHOD__;
 463                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 464                 $loop = new WaitConditionLoop(
 465                         function () use ( $key, $expiry, $fname ) {
 466                                 $this->clearLastError();
 467                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 468                                         return true; // locked!
 469                                 } elseif ( $this->getLastError() ) {
 470                                         $this->logger->warning(
 471                                                 $fname . ' failed due to I/O error for {key}.',
 472                                                 [ 'key' => $key ]
 473                                         );
 474
 475                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 476                                 }
 477
 478                                 return WaitConditionLoop::CONDITION_CONTINUE;
 479                         },
 480                         $timeout
 481                 );
 482
 483                 $code = $loop->invoke();
 484                 $locked = ( $code === $loop::CONDITION_REACHED );
 485                 if ( $locked ) {
 486                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 487                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 488                         $this->logger->warning(
 489                                 "$fname failed due to timeout for {key}.",
 490                                 [ 'key' => $key, 'timeout' => $timeout ]
 491                         );
 492                 }
 493
 494                 return $locked;
 495         }
 496
 497         /**
 498          * Release an advisory lock on a key string
 499          *
 500          * @param string $key
 501          * @return bool Success
 502          */
 503         public function unlock( $key ) {
 504                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 505                         unset( $this->locks[$key] );
 506
 507                         $ok = $this->delete( "{$key}:lock" );
 508                         if ( !$ok ) {
 509                                 $this->logger->warning(
 510                                         __METHOD__ . ' failed to release lock for {key}.',
 511                                         [ 'key' => $key ]
 512                                 );
 513                         }
 514
 515                         return $ok;
 516                 }
 517
 518                 return true;
 519         }
 520
 521         /**
 522          * Get a lightweight exclusive self-unlocking lock
 523          *
 524          * Note that the same lock cannot be acquired twice.
 525          *
 526          * This is useful for task de-duplication or to avoid obtrusive
 527          * (though non-corrupting) DB errors like INSERT key conflicts
 528          * or deadlocks when using LOCK IN SHARE MODE.
 529          *
 530          * @param string $key
 531          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 532          * @param int $expiry Lock expiry [optional]; 1 day maximum
 533          * @param string $rclass Allow reentry if set and the current lock used this value
 534          * @return ScopedCallback|null Returns null on failure
 535          * @since 1.26
 536          */
 537         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 538                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 539
 540                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 541                         return null;
 542                 }
 543
 544                 $lSince = $this->getCurrentTime(); // lock timestamp
 545
 546                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 547                         $latency = 0.050; // latency skew (err towards keeping lock present)
 548                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 549                         if ( ( $age + $latency ) >= $expiry ) {
 550                                 $this->logger->warning(
 551                                         "Lock for {key} held too long ({age} sec).",
 552                                         [ 'key' => $key, 'age' => $age ]
 553                                 );
 554                                 return; // expired; it's not "safe" to delete the key
 555                         }
 556                         $this->unlock( $key );
 557                 } );
 558         }
 559
 560         /**
 561          * Delete all objects expiring before a certain date.
 562          * @param string $date The reference date in MW format
 563          * @param callable|bool $progressCallback Optional, a function which will be called
 564          *     regularly during long-running operations with the percentage progress
 565          *     as the first parameter.
 566          *
 567          * @return bool Success, false if unimplemented
 568          */
 569         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 570                 // stub
 571                 return false;
 572         }
 573
 574         /**
 575          * Get an associative array containing the item for each of the keys that have items.
 576          * @param array $keys List of strings
 577          * @param int $flags Bitfield; supports READ_LATEST [optional]
 578          * @return array
 579          */
 580         public function getMulti( array $keys, $flags = 0 ) {
 581                 $res = [];
 582                 foreach ( $keys as $key ) {
 583                         $val = $this->get( $key );
 584                         if ( $val !== false ) {
 585                                 $res[$key] = $val;
 586                         }
 587                 }
 588                 return $res;
 589         }
 590
 591         /**
 592          * Batch insertion
 593          * @param array $data $key => $value assoc array
 594          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 595          * @return bool Success
 596          * @since 1.24
 597          */
 598         public function setMulti( array $data, $exptime = 0 ) {
 599                 $res = true;
 600                 foreach ( $data as $key => $value ) {
 601                         if ( !$this->set( $key, $value, $exptime ) ) {
 602                                 $res = false;
 603                         }
 604                 }
 605                 return $res;
 606         }
 607
 608         /**
 609          * @param string $key
 610          * @param mixed $value
 611          * @param int $exptime
 612          * @return bool Success
 613          */
 614         public function add( $key, $value, $exptime = 0 ) {
 615                 // @note: avoid lock() here since that method uses *this* method by default
 616                 if ( $this->get( $key ) === false ) {
 617                         return $this->set( $key, $value, $exptime );
 618                 }
 619                 return false; // key already set
 620         }
 621
 622         /**
 623          * Increase stored value of $key by $value while preserving its TTL
 624          * @param string $key Key to increase
 625          * @param int $value Value to add to $key (Default 1)
 626          * @return int|bool New value or false on failure
 627          */
 628         public function incr( $key, $value = 1 ) {
 629                 if ( !$this->lock( $key, 1 ) ) {
 630                         return false;
 631                 }
 632                 $n = $this->get( $key );
 633                 if ( $this->isInteger( $n ) ) { // key exists?
 634                         $n += intval( $value );
 635                         $this->set( $key, max( 0, $n ) ); // exptime?
 636                 } else {
 637                         $n = false;
 638                 }
 639                 $this->unlock( $key );
 640
 641                 return $n;
 642         }
 643
 644         /**
 645          * Decrease stored value of $key by $value while preserving its TTL
 646          * @param string $key
 647          * @param int $value
 648          * @return int|bool New value or false on failure
 649          */
 650         public function decr( $key, $value = 1 ) {
 651                 return $this->incr( $key, - $value );
 652         }
 653
 654         /**
 655          * Increase stored value of $key by $value while preserving its TTL
 656          *
 657          * This will create the key with value $init and TTL $ttl instead if not present
 658          *
 659          * @param string $key
 660          * @param int $ttl
 661          * @param int $value
 662          * @param int $init
 663          * @return int|bool New value or false on failure
 664          * @since 1.24
 665          */
 666         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 667                 $this->clearLastError();
 668                 $newValue = $this->incr( $key, $value );
 669                 if ( $newValue === false && !$this->getLastError() ) {
 670                         // No key set; initialize
 671                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 672                         if ( $newValue === false && !$this->getLastError() ) {
 673                                 // Raced out initializing; increment
 674                                 $newValue = $this->incr( $key, $value );
 675                         }
 676                 }
 677
 678                 return $newValue;
 679         }
 680
 681         /**
 682          * Get the "last error" registered; clearLastError() should be called manually
 683          * @return int ERR_* constant for the "last error" registry
 684          * @since 1.23
 685          */
 686         public function getLastError() {
 687                 return $this->lastError;
 688         }
 689
 690         /**
 691          * Clear the "last error" registry
 692          * @since 1.23
 693          */
 694         public function clearLastError() {
 695                 $this->lastError = self::ERR_NONE;
 696         }
 697
 698         /**
 699          * Set the "last error" registry
 700          * @param int $err ERR_* constant
 701          * @since 1.23
 702          */
 703         protected function setLastError( $err ) {
 704                 $this->lastError = $err;
 705         }
 706
 707         /**
 708          * Let a callback be run to avoid wasting time on special blocking calls
 709          *
 710          * The callbacks may or may not be called ever, in any particular order.
 711          * They are likely to be invoked when something WRITE_SYNC is used used.
 712          * They should follow a caching pattern as shown below, so that any code
 713          * using the word will get it's result no matter what happens.
 714          * @code
 715          *     $result = null;
 716          *     $workCallback = function () use ( &$result ) {
 717          *         if ( !$result ) {
 718          *             $result = ....
 719          *         }
 720          *         return $result;
 721          *     }
 722          * @endcode
 723          *
 724          * @param callable $workCallback
 725          * @since 1.28
 726          */
 727         public function addBusyCallback( callable $workCallback ) {
 728                 $this->busyCallbacks[] = $workCallback;
 729         }
 730
 731         /**
 732          * Modify a cache update operation array for EventRelayer::notify()
 733          *
 734          * This is used for relayed writes, e.g. for broadcasting a change
 735          * to multiple data-centers. If the array contains a 'val' field
 736          * then the command involves setting a key to that value. Note that
 737          * for simplicity, 'val' is always a simple scalar value. This method
 738          * is used to possibly serialize the value and add any cache-specific
 739          * key/values needed for the relayer daemon (e.g. memcached flags).
 740          *
 741          * @param array $event
 742          * @return array
 743          * @since 1.26
 744          */
 745         public function modifySimpleRelayEvent( array $event ) {
 746                 return $event;
 747         }
 748
 749         /**
 750          * @param string $text
 751          */
 752         protected function debug( $text ) {
 753                 if ( $this->debugMode ) {
 754                         $this->logger->debug( "{class} debug: $text", [
 755                                 'class' => static::class,
 756                         ] );
 757                 }
 758         }
 759
 760         /**
 761          * Convert an optionally relative time to an absolute time
 762          * @param int $exptime
 763          * @return int
 764          */
 765         protected function convertExpiry( $exptime ) {
 766                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 767                         return (int)$this->getCurrentTime() + $exptime;
 768                 } else {
 769                         return $exptime;
 770                 }
 771         }
 772
 773         /**
 774          * Convert an optionally absolute expiry time to a relative time. If an
 775          * absolute time is specified which is in the past, use a short expiry time.
 776          *
 777          * @param int $exptime
 778          * @return int
 779          */
 780         protected function convertToRelative( $exptime ) {
 781                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 782                         $exptime -= (int)$this->getCurrentTime();
 783                         if ( $exptime <= 0 ) {
 784                                 $exptime = 1;
 785                         }
 786                         return $exptime;
 787                 } else {
 788                         return $exptime;
 789                 }
 790         }
 791
 792         /**
 793          * Check if a value is an integer
 794          *
 795          * @param mixed $value
 796          * @return bool
 797          */
 798         protected function isInteger( $value ) {
 799                 return ( is_int( $value ) || ctype_digit( $value ) );
 800         }
 801
 802         /**
 803          * Construct a cache key.
 804          *
 805          * @since 1.27
 806          * @param string $keyspace
 807          * @param array $args
 808          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 809          */
 810         public function makeKeyInternal( $keyspace, $args ) {
 811                 $key = $keyspace;
 812                 foreach ( $args as $arg ) {
 813                         $arg = str_replace( ':', '%3A', $arg );
 814                         $key = $key . ':' . $arg;
 815                 }
 816                 return strtr( $key, ' ', '_' );
 817         }
 818
 819         /**
 820          * Make a global cache key.
 821          *
 822          * @since 1.27
 823          * @param string $class Key class
 824          * @param string|null $component [optional] Key component (starting with a key collection name)
 825          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 826          */
 827         public function makeGlobalKey( $class, $component = null ) {
 828                 return $this->makeKeyInternal( 'global', func_get_args() );
 829         }
 830
 831         /**
 832          * Make a cache key, scoped to this instance's keyspace.
 833          *
 834          * @since 1.27
 835          * @param string $class Key class
 836          * @param string|null $component [optional] Key component (starting with a key collection name)
 837          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 838          */
 839         public function makeKey( $class, $component = null ) {
 840                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 841         }
 842
 843         /**
 844          * @param int $flag ATTR_* class constant
 845          * @return int QOS_* class constant
 846          * @since 1.28
 847          */
 848         public function getQoS( $flag ) {
 849                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 850         }
 851
 852         /**
 853          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 854          *
 855          * @param BagOStuff[] $bags
 856          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 857          */
 858         protected function mergeFlagMaps( array $bags ) {
 859                 $map = [];
 860                 foreach ( $bags as $bag ) {
 861                         foreach ( $bag->attrMap as $attr => $rank ) {
 862                                 if ( isset( $map[$attr] ) ) {
 863                                         $map[$attr] = min( $map[$attr], $rank );
 864                                 } else {
 865                                         $map[$attr] = $rank;
 866                                 }
 867                         }
 868                 }
 869
 870                 return $map;
 871         }
 872
 873         /**
 874          * @return float UNIX timestamp
 875          * @codeCoverageIgnore
 876          */
 877         protected function getCurrentTime() {
 878                 return $this->wallClockOverride ?: microtime( true );
 879         }
 880
 881         /**
 882          * @param float|null &$time Mock UNIX timestamp for testing
 883          * @codeCoverageIgnore
 884          */
 885         public function setMockTime( &$time ) {
 886                 $this->wallClockOverride =& $time;
 887         }
 888 }