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->mergeViaCas( $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                         $hadNoCurrentValue = ( $currentValue === false );
 315                         unset( $currentValue ); // free RAM in case the value is large
 316
 317                         $this->clearLastError();
 318                         if ( $value === false ) {
 319                                 $success = true; // do nothing
 320                         } elseif ( $hadNoCurrentValue ) {
 321                                 // Try to create the key, failing if it gets created in the meantime
 322                                 $success = $this->add( $key, $value, $exptime, $flags );
 323                         } else {
 324                                 // Try to update the key, failing if it gets changed in the meantime
 325                                 $success = $this->cas( $casToken, $key, $value, $exptime, $flags );
 326                         }
 327                         if ( $this->getLastError() ) {
 328                                 $this->logger->warning(
 329                                         __METHOD__ . ' failed due to I/O error for {key}.',
 330                                         [ 'key' => $key ]
 331                                 );
 332
 333                                 return false; // IO error; don't spam retries
 334                         }
 335                 } while ( !$success && --$attempts );
 336
 337                 return $success;
 338         }
 339
 340         /**
 341          * Check and set an item
 342          *
 343          * @param mixed $casToken
 344          * @param string $key
 345          * @param mixed $value
 346          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 347          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 348          * @return bool Success
 349          * @throws Exception
 350          */
 351         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 352                 if ( !$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, $flags );
 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          * Change the expiration on a key if it exists
 376          *
 377          * If an expiry in the past is given then the key will immediately be expired
 378          *
 379          * @param string $key
 380          * @param int $expiry TTL or UNIX timestamp
 381          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 382          * @return bool Success Returns false on failure or if the item does not exist
 383          * @since 1.28
 384          */
 385         public function changeTTL( $key, $expiry = 0, $flags = 0 ) {
 386                 $found = false;
 387
 388                 $ok = $this->merge(
 389                         $key,
 390                         function ( $cache, $ttl, $currentValue ) use ( &$found ) {
 391                                 $found = ( $currentValue !== false );
 392
 393                                 return $currentValue; // nothing is written if this is false
 394                         },
 395                         $expiry,
 396                         1, // 1 attempt
 397                         $flags
 398                 );
 399
 400                 return ( $ok && $found );
 401         }
 402
 403         /**
 404          * Acquire an advisory lock on a key string
 405          *
 406          * Note that if reentry is enabled, duplicate calls ignore $expiry
 407          *
 408          * @param string $key
 409          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 410          * @param int $expiry Lock expiry [optional]; 1 day maximum
 411          * @param string $rclass Allow reentry if set and the current lock used this value
 412          * @return bool Success
 413          */
 414         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 415                 // Avoid deadlocks and allow lock reentry if specified
 416                 if ( isset( $this->locks[$key] ) ) {
 417                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 418                                 ++$this->locks[$key]['depth'];
 419                                 return true;
 420                         } else {
 421                                 return false;
 422                         }
 423                 }
 424
 425                 $fname = __METHOD__;
 426                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 427                 $loop = new WaitConditionLoop(
 428                         function () use ( $key, $expiry, $fname ) {
 429                                 $this->clearLastError();
 430                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 431                                         return WaitConditionLoop::CONDITION_REACHED; // locked!
 432                                 } elseif ( $this->getLastError() ) {
 433                                         $this->logger->warning(
 434                                                 $fname . ' failed due to I/O error for {key}.',
 435                                                 [ 'key' => $key ]
 436                                         );
 437
 438                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 439                                 }
 440
 441                                 return WaitConditionLoop::CONDITION_CONTINUE;
 442                         },
 443                         $timeout
 444                 );
 445
 446                 $code = $loop->invoke();
 447                 $locked = ( $code === $loop::CONDITION_REACHED );
 448                 if ( $locked ) {
 449                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 450                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 451                         $this->logger->warning(
 452                                 "$fname failed due to timeout for {key}.",
 453                                 [ 'key' => $key, 'timeout' => $timeout ]
 454                         );
 455                 }
 456
 457                 return $locked;
 458         }
 459
 460         /**
 461          * Release an advisory lock on a key string
 462          *
 463          * @param string $key
 464          * @return bool Success
 465          */
 466         public function unlock( $key ) {
 467                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 468                         unset( $this->locks[$key] );
 469
 470                         $ok = $this->delete( "{$key}:lock" );
 471                         if ( !$ok ) {
 472                                 $this->logger->warning(
 473                                         __METHOD__ . ' failed to release lock for {key}.',
 474                                         [ 'key' => $key ]
 475                                 );
 476                         }
 477
 478                         return $ok;
 479                 }
 480
 481                 return true;
 482         }
 483
 484         /**
 485          * Get a lightweight exclusive self-unlocking lock
 486          *
 487          * Note that the same lock cannot be acquired twice.
 488          *
 489          * This is useful for task de-duplication or to avoid obtrusive
 490          * (though non-corrupting) DB errors like INSERT key conflicts
 491          * or deadlocks when using LOCK IN SHARE MODE.
 492          *
 493          * @param string $key
 494          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 495          * @param int $expiry Lock expiry [optional]; 1 day maximum
 496          * @param string $rclass Allow reentry if set and the current lock used this value
 497          * @return ScopedCallback|null Returns null on failure
 498          * @since 1.26
 499          */
 500         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 501                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 502
 503                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 504                         return null;
 505                 }
 506
 507                 $lSince = $this->getCurrentTime(); // lock timestamp
 508
 509                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 510                         $latency = 0.050; // latency skew (err towards keeping lock present)
 511                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 512                         if ( ( $age + $latency ) >= $expiry ) {
 513                                 $this->logger->warning(
 514                                         "Lock for {key} held too long ({age} sec).",
 515                                         [ 'key' => $key, 'age' => $age ]
 516                                 );
 517                                 return; // expired; it's not "safe" to delete the key
 518                         }
 519                         $this->unlock( $key );
 520                 } );
 521         }
 522
 523         /**
 524          * Delete all objects expiring before a certain date.
 525          * @param string $date The reference date in MW format
 526          * @param callable|bool $progressCallback Optional, a function which will be called
 527          *     regularly during long-running operations with the percentage progress
 528          *     as the first parameter.
 529          *
 530          * @return bool Success, false if unimplemented
 531          */
 532         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 533                 // stub
 534                 return false;
 535         }
 536
 537         /**
 538          * Get an associative array containing the item for each of the keys that have items.
 539          * @param string[] $keys List of keys
 540          * @param int $flags Bitfield; supports READ_LATEST [optional]
 541          * @return array
 542          */
 543         public function getMulti( array $keys, $flags = 0 ) {
 544                 $res = [];
 545                 foreach ( $keys as $key ) {
 546                         $val = $this->get( $key, $flags );
 547                         if ( $val !== false ) {
 548                                 $res[$key] = $val;
 549                         }
 550                 }
 551
 552                 return $res;
 553         }
 554
 555         /**
 556          * Batch insertion/replace
 557          * @param mixed[] $data Map of (key => value)
 558          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 559          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 560          * @return bool Success
 561          * @since 1.24
 562          */
 563         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 564                 $res = true;
 565                 foreach ( $data as $key => $value ) {
 566                         if ( !$this->set( $key, $value, $exptime, $flags ) ) {
 567                                 $res = false;
 568                         }
 569                 }
 570
 571                 return $res;
 572         }
 573
 574         /**
 575          * Batch deletion
 576          * @param string[] $keys List of keys
 577          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 578          * @return bool Success
 579          * @since 1.33
 580          */
 581         public function deleteMulti( array $keys, $flags = 0 ) {
 582                 $res = true;
 583                 foreach ( $keys as $key ) {
 584                         $res = $this->delete( $key, $flags ) && $res;
 585                 }
 586
 587                 return $res;
 588         }
 589
 590         /**
 591          * Insertion
 592          * @param string $key
 593          * @param mixed $value
 594          * @param int $exptime
 595          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 596          * @return bool Success
 597          */
 598         abstract public function add( $key, $value, $exptime = 0, $flags = 0 );
 599
 600         /**
 601          * Increase stored value of $key by $value while preserving its TTL
 602          * @param string $key Key to increase
 603          * @param int $value Value to add to $key (default: 1) [optional]
 604          * @return int|bool New value or false on failure
 605          */
 606         abstract public function incr( $key, $value = 1 );
 607
 608         /**
 609          * Decrease stored value of $key by $value while preserving its TTL
 610          * @param string $key
 611          * @param int $value Value to subtract from $key (default: 1) [optional]
 612          * @return int|bool New value or false on failure
 613          */
 614         public function decr( $key, $value = 1 ) {
 615                 return $this->incr( $key, - $value );
 616         }
 617
 618         /**
 619          * Increase stored value of $key by $value while preserving its TTL
 620          *
 621          * This will create the key with value $init and TTL $ttl instead if not present
 622          *
 623          * @param string $key
 624          * @param int $ttl
 625          * @param int $value
 626          * @param int $init
 627          * @return int|bool New value or false on failure
 628          * @since 1.24
 629          */
 630         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 631                 $this->clearLastError();
 632                 $newValue = $this->incr( $key, $value );
 633                 if ( $newValue === false && !$this->getLastError() ) {
 634                         // No key set; initialize
 635                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 636                         if ( $newValue === false && !$this->getLastError() ) {
 637                                 // Raced out initializing; increment
 638                                 $newValue = $this->incr( $key, $value );
 639                         }
 640                 }
 641
 642                 return $newValue;
 643         }
 644
 645         /**
 646          * Get the "last error" registered; clearLastError() should be called manually
 647          * @return int ERR_* constant for the "last error" registry
 648          * @since 1.23
 649          */
 650         public function getLastError() {
 651                 return $this->lastError;
 652         }
 653
 654         /**
 655          * Clear the "last error" registry
 656          * @since 1.23
 657          */
 658         public function clearLastError() {
 659                 $this->lastError = self::ERR_NONE;
 660         }
 661
 662         /**
 663          * Set the "last error" registry
 664          * @param int $err ERR_* constant
 665          * @since 1.23
 666          */
 667         protected function setLastError( $err ) {
 668                 $this->lastError = $err;
 669         }
 670
 671         /**
 672          * Let a callback be run to avoid wasting time on special blocking calls
 673          *
 674          * The callbacks may or may not be called ever, in any particular order.
 675          * They are likely to be invoked when something WRITE_SYNC is used used.
 676          * They should follow a caching pattern as shown below, so that any code
 677          * using the work will get it's result no matter what happens.
 678          * @code
 679          *     $result = null;
 680          *     $workCallback = function () use ( &$result ) {
 681          *         if ( !$result ) {
 682          *             $result = ....
 683          *         }
 684          *         return $result;
 685          *     }
 686          * @endcode
 687          *
 688          * @param callable $workCallback
 689          * @since 1.28
 690          */
 691         public function addBusyCallback( callable $workCallback ) {
 692                 $this->busyCallbacks[] = $workCallback;
 693         }
 694
 695         /**
 696          * @param string $text
 697          */
 698         protected function debug( $text ) {
 699                 if ( $this->debugMode ) {
 700                         $this->logger->debug( "{class} debug: $text", [
 701                                 'class' => static::class,
 702                         ] );
 703                 }
 704         }
 705
 706         /**
 707          * Convert an optionally relative time to an absolute time
 708          * @param int $exptime
 709          * @return int
 710          */
 711         protected function convertExpiry( $exptime ) {
 712                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 713                         return (int)$this->getCurrentTime() + $exptime;
 714                 } else {
 715                         return $exptime;
 716                 }
 717         }
 718
 719         /**
 720          * Convert an optionally absolute expiry time to a relative time. If an
 721          * absolute time is specified which is in the past, use a short expiry time.
 722          *
 723          * @param int $exptime
 724          * @return int
 725          */
 726         protected function convertToRelative( $exptime ) {
 727                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 728                         $exptime -= (int)$this->getCurrentTime();
 729                         if ( $exptime <= 0 ) {
 730                                 $exptime = 1;
 731                         }
 732                         return $exptime;
 733                 } else {
 734                         return $exptime;
 735                 }
 736         }
 737
 738         /**
 739          * Check if a value is an integer
 740          *
 741          * @param mixed $value
 742          * @return bool
 743          */
 744         protected function isInteger( $value ) {
 745                 return ( is_int( $value ) || ctype_digit( $value ) );
 746         }
 747
 748         /**
 749          * Construct a cache key.
 750          *
 751          * @since 1.27
 752          * @param string $keyspace
 753          * @param array $args
 754          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 755          */
 756         public function makeKeyInternal( $keyspace, $args ) {
 757                 $key = $keyspace;
 758                 foreach ( $args as $arg ) {
 759                         $key .= ':' . str_replace( ':', '%3A', $arg );
 760                 }
 761                 return strtr( $key, ' ', '_' );
 762         }
 763
 764         /**
 765          * Make a global cache key.
 766          *
 767          * @since 1.27
 768          * @param string $class Key class
 769          * @param string|null $component [optional] Key component (starting with a key collection name)
 770          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 771          */
 772         public function makeGlobalKey( $class, $component = null ) {
 773                 return $this->makeKeyInternal( 'global', func_get_args() );
 774         }
 775
 776         /**
 777          * Make a cache key, scoped to this instance's keyspace.
 778          *
 779          * @since 1.27
 780          * @param string $class Key class
 781          * @param string|null $component [optional] Key component (starting with a key collection name)
 782          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 783          */
 784         public function makeKey( $class, $component = null ) {
 785                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 786         }
 787
 788         /**
 789          * @param int $flag ATTR_* class constant
 790          * @return int QOS_* class constant
 791          * @since 1.28
 792          */
 793         public function getQoS( $flag ) {
 794                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 795         }
 796
 797         /**
 798          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 799          *
 800          * @param BagOStuff[] $bags
 801          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 802          */
 803         protected function mergeFlagMaps( array $bags ) {
 804                 $map = [];
 805                 foreach ( $bags as $bag ) {
 806                         foreach ( $bag->attrMap as $attr => $rank ) {
 807                                 if ( isset( $map[$attr] ) ) {
 808                                         $map[$attr] = min( $map[$attr], $rank );
 809                                 } else {
 810                                         $map[$attr] = $rank;
 811                                 }
 812                         }
 813                 }
 814
 815                 return $map;
 816         }
 817
 818         /**
 819          * @return float UNIX timestamp
 820          * @codeCoverageIgnore
 821          */
 822         protected function getCurrentTime() {
 823                 return $this->wallClockOverride ?: microtime( true );
 824         }
 825
 826         /**
 827          * @param float|null &$time Mock UNIX timestamp for testing
 828          * @codeCoverageIgnore
 829          */
 830         public function setMockTime( &$time ) {
 831                 $this->wallClockOverride =& $time;
 832         }
 833 }