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          * @return mixed Returns false on failure or if the item does not exist
 179          */
 180         public function get( $key, $flags = 0 ) {
 181                 $this->trackDuplicateKeys( $key );
 182
 183                 return $this->doGet( $key, $flags );
 184         }
 185
 186         /**
 187          * Track the number of times that a given key has been used.
 188          * @param string $key
 189          */
 190         private function trackDuplicateKeys( $key ) {
 191                 if ( !$this->reportDupes ) {
 192                         return;
 193                 }
 194
 195                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 196                         // Track that we have seen this key. This N-1 counting style allows
 197                         // easy filtering with array_filter() later.
 198                         $this->duplicateKeyLookups[$key] = 0;
 199                 } else {
 200                         $this->duplicateKeyLookups[$key] += 1;
 201
 202                         if ( $this->dupeTrackScheduled === false ) {
 203                                 $this->dupeTrackScheduled = true;
 204                                 // Schedule a callback that logs keys processed more than once by get().
 205                                 call_user_func( $this->asyncHandler, function () {
 206                                         $dups = array_filter( $this->duplicateKeyLookups );
 207                                         foreach ( $dups as $key => $count ) {
 208                                                 $this->logger->warning(
 209                                                         'Duplicate get(): "{key}" fetched {count} times',
 210                                                         // Count is N-1 of the actual lookup count
 211                                                         [ 'key' => $key, 'count' => $count + 1, ]
 212                                                 );
 213                                         }
 214                                 } );
 215                         }
 216                 }
 217         }
 218
 219         /**
 220          * @param string $key
 221          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 222          * @param mixed|null &$casToken Token to use for check-and-set comparisons
 223          * @return mixed Returns false on failure or if the item does not exist
 224          */
 225         abstract protected function doGet( $key, $flags = 0, &$casToken = null );
 226
 227         /**
 228          * Set an item
 229          *
 230          * @param string $key
 231          * @param mixed $value
 232          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 233          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 234          * @return bool Success
 235          */
 236         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 237
 238         /**
 239          * Delete an item
 240          *
 241          * @param string $key
 242          * @return bool True if the item was deleted or not found, false on failure
 243          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 244          */
 245         abstract public function delete( $key, $flags = 0 );
 246
 247         /**
 248          * Insert an item if it does not already exist
 249          *
 250          * @param string $key
 251          * @param mixed $value
 252          * @param int $exptime
 253          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 254          * @return bool Success
 255          */
 256         abstract public function add( $key, $value, $exptime = 0, $flags = 0 );
 257
 258         /**
 259          * Merge changes into the existing cache value (possibly creating a new one)
 260          *
 261          * The callback function returns the new value given the current value
 262          * (which will be false if not present), and takes the arguments:
 263          * (this BagOStuff, cache key, current value, TTL).
 264          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 265          * Nothing is stored nor deleted if the callback returns false.
 266          *
 267          * @param string $key
 268          * @param callable $callback Callback method to be executed
 269          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 270          * @param int $attempts The amount of times to attempt a merge in case of failure
 271          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 272          * @return bool Success
 273          * @throws InvalidArgumentException
 274          */
 275         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 276                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
 277         }
 278
 279         /**
 280          * @see BagOStuff::merge()
 281          *
 282          * @param string $key
 283          * @param callable $callback Callback method to be executed
 284          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 285          * @param int $attempts The amount of times to attempt a merge in case of failure
 286          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 287          * @return bool Success
 288          */
 289         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 290                 do {
 291                         $this->clearLastError();
 292                         $reportDupes = $this->reportDupes;
 293                         $this->reportDupes = false;
 294                         $casToken = null; // passed by reference
 295                         $currentValue = $this->doGet( $key, self::READ_LATEST, $casToken );
 296                         $this->reportDupes = $reportDupes;
 297
 298                         if ( $this->getLastError() ) {
 299                                 $this->logger->warning(
 300                                         __METHOD__ . ' failed due to I/O error on get() for {key}.',
 301                                         [ 'key' => $key ]
 302                                 );
 303
 304                                 return false; // don't spam retries (retry only on races)
 305                         }
 306
 307                         // Derive the new value from the old value
 308                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 309                         $hadNoCurrentValue = ( $currentValue === false );
 310                         unset( $currentValue ); // free RAM in case the value is large
 311
 312                         $this->clearLastError();
 313                         if ( $value === false ) {
 314                                 $success = true; // do nothing
 315                         } elseif ( $hadNoCurrentValue ) {
 316                                 // Try to create the key, failing if it gets created in the meantime
 317                                 $success = $this->add( $key, $value, $exptime, $flags );
 318                         } else {
 319                                 // Try to update the key, failing if it gets changed in the meantime
 320                                 $success = $this->cas( $casToken, $key, $value, $exptime, $flags );
 321                         }
 322                         if ( $this->getLastError() ) {
 323                                 $this->logger->warning(
 324                                         __METHOD__ . ' failed due to I/O error for {key}.',
 325                                         [ 'key' => $key ]
 326                                 );
 327
 328                                 return false; // IO error; don't spam retries
 329                         }
 330                 } while ( !$success && --$attempts );
 331
 332                 return $success;
 333         }
 334
 335         /**
 336          * Check and set an item
 337          *
 338          * @param mixed $casToken
 339          * @param string $key
 340          * @param mixed $value
 341          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 342          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 343          * @return bool Success
 344          * @throws Exception
 345          */
 346         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 347                 if ( !$this->lock( $key, 0 ) ) {
 348                         return false; // non-blocking
 349                 }
 350
 351                 $curCasToken = null; // passed by reference
 352                 $this->doGet( $key, self::READ_LATEST, $curCasToken );
 353                 if ( $casToken === $curCasToken ) {
 354                         $success = $this->set( $key, $value, $exptime, $flags );
 355                 } else {
 356                         $this->logger->info(
 357                                 __METHOD__ . ' failed due to race condition for {key}.',
 358                                 [ 'key' => $key ]
 359                         );
 360
 361                         $success = false; // mismatched or failed
 362                 }
 363
 364                 $this->unlock( $key );
 365
 366                 return $success;
 367         }
 368
 369         /**
 370          * Change the expiration on a key if it exists
 371          *
 372          * If an expiry in the past is given then the key will immediately be expired
 373          *
 374          * @param string $key
 375          * @param int $expiry TTL or UNIX timestamp
 376          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 377          * @return bool Success Returns false on failure or if the item does not exist
 378          * @since 1.28
 379          */
 380         public function changeTTL( $key, $expiry = 0, $flags = 0 ) {
 381                 $found = false;
 382
 383                 $ok = $this->merge(
 384                         $key,
 385                         function ( $cache, $ttl, $currentValue ) use ( &$found ) {
 386                                 $found = ( $currentValue !== false );
 387
 388                                 return $currentValue; // nothing is written if this is false
 389                         },
 390                         $expiry,
 391                         1, // 1 attempt
 392                         $flags
 393                 );
 394
 395                 return ( $ok && $found );
 396         }
 397
 398         /**
 399          * Acquire an advisory lock on a key string
 400          *
 401          * Note that if reentry is enabled, duplicate calls ignore $expiry
 402          *
 403          * @param string $key
 404          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 405          * @param int $expiry Lock expiry [optional]; 1 day maximum
 406          * @param string $rclass Allow reentry if set and the current lock used this value
 407          * @return bool Success
 408          */
 409         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 410                 // Avoid deadlocks and allow lock reentry if specified
 411                 if ( isset( $this->locks[$key] ) ) {
 412                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 413                                 ++$this->locks[$key]['depth'];
 414                                 return true;
 415                         } else {
 416                                 return false;
 417                         }
 418                 }
 419
 420                 $fname = __METHOD__;
 421                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 422                 $loop = new WaitConditionLoop(
 423                         function () use ( $key, $expiry, $fname ) {
 424                                 $this->clearLastError();
 425                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 426                                         return WaitConditionLoop::CONDITION_REACHED; // locked!
 427                                 } elseif ( $this->getLastError() ) {
 428                                         $this->logger->warning(
 429                                                 $fname . ' failed due to I/O error for {key}.',
 430                                                 [ 'key' => $key ]
 431                                         );
 432
 433                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 434                                 }
 435
 436                                 return WaitConditionLoop::CONDITION_CONTINUE;
 437                         },
 438                         $timeout
 439                 );
 440
 441                 $code = $loop->invoke();
 442                 $locked = ( $code === $loop::CONDITION_REACHED );
 443                 if ( $locked ) {
 444                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 445                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 446                         $this->logger->warning(
 447                                 "$fname failed due to timeout for {key}.",
 448                                 [ 'key' => $key, 'timeout' => $timeout ]
 449                         );
 450                 }
 451
 452                 return $locked;
 453         }
 454
 455         /**
 456          * Release an advisory lock on a key string
 457          *
 458          * @param string $key
 459          * @return bool Success
 460          */
 461         public function unlock( $key ) {
 462                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 463                         unset( $this->locks[$key] );
 464
 465                         $ok = $this->delete( "{$key}:lock" );
 466                         if ( !$ok ) {
 467                                 $this->logger->warning(
 468                                         __METHOD__ . ' failed to release lock for {key}.',
 469                                         [ 'key' => $key ]
 470                                 );
 471                         }
 472
 473                         return $ok;
 474                 }
 475
 476                 return true;
 477         }
 478
 479         /**
 480          * Get a lightweight exclusive self-unlocking lock
 481          *
 482          * Note that the same lock cannot be acquired twice.
 483          *
 484          * This is useful for task de-duplication or to avoid obtrusive
 485          * (though non-corrupting) DB errors like INSERT key conflicts
 486          * or deadlocks when using LOCK IN SHARE MODE.
 487          *
 488          * @param string $key
 489          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 490          * @param int $expiry Lock expiry [optional]; 1 day maximum
 491          * @param string $rclass Allow reentry if set and the current lock used this value
 492          * @return ScopedCallback|null Returns null on failure
 493          * @since 1.26
 494          */
 495         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 496                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 497
 498                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 499                         return null;
 500                 }
 501
 502                 $lSince = $this->getCurrentTime(); // lock timestamp
 503
 504                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 505                         $latency = 0.050; // latency skew (err towards keeping lock present)
 506                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 507                         if ( ( $age + $latency ) >= $expiry ) {
 508                                 $this->logger->warning(
 509                                         "Lock for {key} held too long ({age} sec).",
 510                                         [ 'key' => $key, 'age' => $age ]
 511                                 );
 512                                 return; // expired; it's not "safe" to delete the key
 513                         }
 514                         $this->unlock( $key );
 515                 } );
 516         }
 517
 518         /**
 519          * Delete all objects expiring before a certain date.
 520          * @param string $date The reference date in MW format
 521          * @param callable|bool $progressCallback Optional, a function which will be called
 522          *     regularly during long-running operations with the percentage progress
 523          *     as the first parameter.
 524          *
 525          * @return bool Success, false if unimplemented
 526          */
 527         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 528                 // stub
 529                 return false;
 530         }
 531
 532         /**
 533          * Get an associative array containing the item for each of the keys that have items.
 534          * @param string[] $keys List of keys
 535          * @param int $flags Bitfield; supports READ_LATEST [optional]
 536          * @return array
 537          */
 538         public function getMulti( array $keys, $flags = 0 ) {
 539                 $res = [];
 540                 foreach ( $keys as $key ) {
 541                         $val = $this->get( $key, $flags );
 542                         if ( $val !== false ) {
 543                                 $res[$key] = $val;
 544                         }
 545                 }
 546
 547                 return $res;
 548         }
 549
 550         /**
 551          * Batch insertion/replace
 552          * @param mixed[] $data Map of (key => value)
 553          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 554          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 555          * @return bool Success
 556          * @since 1.24
 557          */
 558         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 559                 $res = true;
 560                 foreach ( $data as $key => $value ) {
 561                         if ( !$this->set( $key, $value, $exptime, $flags ) ) {
 562                                 $res = false;
 563                         }
 564                 }
 565
 566                 return $res;
 567         }
 568
 569         /**
 570          * Batch deletion
 571          * @param string[] $keys List of keys
 572          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 573          * @return bool Success
 574          * @since 1.33
 575          */
 576         public function deleteMulti( array $keys, $flags = 0 ) {
 577                 $res = true;
 578                 foreach ( $keys as $key ) {
 579                         $res = $this->delete( $key, $flags ) && $res;
 580                 }
 581
 582                 return $res;
 583         }
 584
 585         /**
 586          * Increase stored value of $key by $value while preserving its TTL
 587          * @param string $key Key to increase
 588          * @param int $value Value to add to $key (default: 1) [optional]
 589          * @return int|bool New value or false on failure
 590          */
 591         abstract public function incr( $key, $value = 1 );
 592
 593         /**
 594          * Decrease stored value of $key by $value while preserving its TTL
 595          * @param string $key
 596          * @param int $value Value to subtract from $key (default: 1) [optional]
 597          * @return int|bool New value or false on failure
 598          */
 599         public function decr( $key, $value = 1 ) {
 600                 return $this->incr( $key, - $value );
 601         }
 602
 603         /**
 604          * Increase stored value of $key by $value while preserving its TTL
 605          *
 606          * This will create the key with value $init and TTL $ttl instead if not present
 607          *
 608          * @param string $key
 609          * @param int $ttl
 610          * @param int $value
 611          * @param int $init
 612          * @return int|bool New value or false on failure
 613          * @since 1.24
 614          */
 615         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 616                 $this->clearLastError();
 617                 $newValue = $this->incr( $key, $value );
 618                 if ( $newValue === false && !$this->getLastError() ) {
 619                         // No key set; initialize
 620                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 621                         if ( $newValue === false && !$this->getLastError() ) {
 622                                 // Raced out initializing; increment
 623                                 $newValue = $this->incr( $key, $value );
 624                         }
 625                 }
 626
 627                 return $newValue;
 628         }
 629
 630         /**
 631          * Get the "last error" registered; clearLastError() should be called manually
 632          * @return int ERR_* constant for the "last error" registry
 633          * @since 1.23
 634          */
 635         public function getLastError() {
 636                 return $this->lastError;
 637         }
 638
 639         /**
 640          * Clear the "last error" registry
 641          * @since 1.23
 642          */
 643         public function clearLastError() {
 644                 $this->lastError = self::ERR_NONE;
 645         }
 646
 647         /**
 648          * Set the "last error" registry
 649          * @param int $err ERR_* constant
 650          * @since 1.23
 651          */
 652         protected function setLastError( $err ) {
 653                 $this->lastError = $err;
 654         }
 655
 656         /**
 657          * Let a callback be run to avoid wasting time on special blocking calls
 658          *
 659          * The callbacks may or may not be called ever, in any particular order.
 660          * They are likely to be invoked when something WRITE_SYNC is used used.
 661          * They should follow a caching pattern as shown below, so that any code
 662          * using the work will get it's result no matter what happens.
 663          * @code
 664          *     $result = null;
 665          *     $workCallback = function () use ( &$result ) {
 666          *         if ( !$result ) {
 667          *             $result = ....
 668          *         }
 669          *         return $result;
 670          *     }
 671          * @endcode
 672          *
 673          * @param callable $workCallback
 674          * @since 1.28
 675          */
 676         public function addBusyCallback( callable $workCallback ) {
 677                 $this->busyCallbacks[] = $workCallback;
 678         }
 679
 680         /**
 681          * @param string $text
 682          */
 683         protected function debug( $text ) {
 684                 if ( $this->debugMode ) {
 685                         $this->logger->debug( "{class} debug: $text", [
 686                                 'class' => static::class,
 687                         ] );
 688                 }
 689         }
 690
 691         /**
 692          * @param int $exptime
 693          * @return bool
 694          */
 695         protected function expiryIsRelative( $exptime ) {
 696                 return ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) );
 697         }
 698
 699         /**
 700          * Convert an optionally relative time to an absolute time
 701          * @param int $exptime
 702          * @return int
 703          */
 704         protected function convertToExpiry( $exptime ) {
 705                 if ( $this->expiryIsRelative( $exptime ) ) {
 706                         return (int)$this->getCurrentTime() + $exptime;
 707                 } else {
 708                         return $exptime;
 709                 }
 710         }
 711
 712         /**
 713          * Convert an optionally absolute expiry time to a relative time. If an
 714          * absolute time is specified which is in the past, use a short expiry time.
 715          *
 716          * @param int $exptime
 717          * @return int
 718          */
 719         protected function convertToRelative( $exptime ) {
 720                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 721                         $exptime -= (int)$this->getCurrentTime();
 722                         if ( $exptime <= 0 ) {
 723                                 $exptime = 1;
 724                         }
 725                         return $exptime;
 726                 } else {
 727                         return $exptime;
 728                 }
 729         }
 730
 731         /**
 732          * Check if a value is an integer
 733          *
 734          * @param mixed $value
 735          * @return bool
 736          */
 737         protected function isInteger( $value ) {
 738                 return ( is_int( $value ) || ctype_digit( $value ) );
 739         }
 740
 741         /**
 742          * Construct a cache key.
 743          *
 744          * @since 1.27
 745          * @param string $keyspace
 746          * @param array $args
 747          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 748          */
 749         public function makeKeyInternal( $keyspace, $args ) {
 750                 $key = $keyspace;
 751                 foreach ( $args as $arg ) {
 752                         $key .= ':' . str_replace( ':', '%3A', $arg );
 753                 }
 754                 return strtr( $key, ' ', '_' );
 755         }
 756
 757         /**
 758          * Make a global cache key.
 759          *
 760          * @since 1.27
 761          * @param string $class Key class
 762          * @param string|null $component [optional] Key component (starting with a key collection name)
 763          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 764          */
 765         public function makeGlobalKey( $class, $component = null ) {
 766                 return $this->makeKeyInternal( 'global', func_get_args() );
 767         }
 768
 769         /**
 770          * Make a cache key, scoped to this instance's keyspace.
 771          *
 772          * @since 1.27
 773          * @param string $class Key class
 774          * @param string|null $component [optional] Key component (starting with a key collection name)
 775          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 776          */
 777         public function makeKey( $class, $component = null ) {
 778                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 779         }
 780
 781         /**
 782          * @param int $flag ATTR_* class constant
 783          * @return int QOS_* class constant
 784          * @since 1.28
 785          */
 786         public function getQoS( $flag ) {
 787                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 788         }
 789
 790         /**
 791          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 792          *
 793          * @param BagOStuff[] $bags
 794          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 795          */
 796         protected function mergeFlagMaps( array $bags ) {
 797                 $map = [];
 798                 foreach ( $bags as $bag ) {
 799                         foreach ( $bag->attrMap as $attr => $rank ) {
 800                                 if ( isset( $map[$attr] ) ) {
 801                                         $map[$attr] = min( $map[$attr], $rank );
 802                                 } else {
 803                                         $map[$attr] = $rank;
 804                                 }
 805                         }
 806                 }
 807
 808                 return $map;
 809         }
 810
 811         /**
 812          * @return float UNIX timestamp
 813          * @codeCoverageIgnore
 814          */
 815         protected function getCurrentTime() {
 816                 return $this->wallClockOverride ?: microtime( true );
 817         }
 818
 819         /**
 820          * @param float|null &$time Mock UNIX timestamp for testing
 821          * @codeCoverageIgnore
 822          */
 823         public function setMockTime( &$time ) {
 824                 $this->wallClockOverride =& $time;
 825         }
 826 }