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          * Insert an item if it does not already exist
 265          *
 266          * @param string $key
 267          * @param mixed $value
 268          * @param int $exptime
 269          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 270          * @return bool Success
 271          */
 272         abstract public function add( $key, $value, $exptime = 0, $flags = 0 );
 273
 274         /**
 275          * Merge changes into the existing cache value (possibly creating a new one)
 276          *
 277          * The callback function returns the new value given the current value
 278          * (which will be false if not present), and takes the arguments:
 279          * (this BagOStuff, cache key, current value, TTL).
 280          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 281          * Nothing is stored nor deleted if the callback returns false.
 282          *
 283          * @param string $key
 284          * @param callable $callback Callback method to be executed
 285          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 286          * @param int $attempts The amount of times to attempt a merge in case of failure
 287          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 288          * @return bool Success
 289          * @throws InvalidArgumentException
 290          */
 291         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 292                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts, $flags );
 293         }
 294
 295         /**
 296          * @see BagOStuff::merge()
 297          *
 298          * @param string $key
 299          * @param callable $callback Callback method to be executed
 300          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 301          * @param int $attempts The amount of times to attempt a merge in case of failure
 302          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 303          * @return bool Success
 304          */
 305         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 306                 do {
 307                         $this->clearLastError();
 308                         $reportDupes = $this->reportDupes;
 309                         $this->reportDupes = false;
 310                         $casToken = null; // passed by reference
 311                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 312                         $this->reportDupes = $reportDupes;
 313
 314                         if ( $this->getLastError() ) {
 315                                 $this->logger->warning(
 316                                         __METHOD__ . ' failed due to I/O error on get() for {key}.',
 317                                         [ 'key' => $key ]
 318                                 );
 319
 320                                 return false; // don't spam retries (retry only on races)
 321                         }
 322
 323                         // Derive the new value from the old value
 324                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 325                         $hadNoCurrentValue = ( $currentValue === false );
 326                         unset( $currentValue ); // free RAM in case the value is large
 327
 328                         $this->clearLastError();
 329                         if ( $value === false ) {
 330                                 $success = true; // do nothing
 331                         } elseif ( $hadNoCurrentValue ) {
 332                                 // Try to create the key, failing if it gets created in the meantime
 333                                 $success = $this->add( $key, $value, $exptime, $flags );
 334                         } else {
 335                                 // Try to update the key, failing if it gets changed in the meantime
 336                                 $success = $this->cas( $casToken, $key, $value, $exptime, $flags );
 337                         }
 338                         if ( $this->getLastError() ) {
 339                                 $this->logger->warning(
 340                                         __METHOD__ . ' failed due to I/O error for {key}.',
 341                                         [ 'key' => $key ]
 342                                 );
 343
 344                                 return false; // IO error; don't spam retries
 345                         }
 346                 } while ( !$success && --$attempts );
 347
 348                 return $success;
 349         }
 350
 351         /**
 352          * Check and set an item
 353          *
 354          * @param mixed $casToken
 355          * @param string $key
 356          * @param mixed $value
 357          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 358          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 359          * @return bool Success
 360          * @throws Exception
 361          */
 362         protected function cas( $casToken, $key, $value, $exptime = 0, $flags = 0 ) {
 363                 if ( !$this->lock( $key, 0 ) ) {
 364                         return false; // non-blocking
 365                 }
 366
 367                 $curCasToken = null; // passed by reference
 368                 $this->getWithToken( $key, $curCasToken, self::READ_LATEST );
 369                 if ( $casToken === $curCasToken ) {
 370                         $success = $this->set( $key, $value, $exptime, $flags );
 371                 } else {
 372                         $this->logger->info(
 373                                 __METHOD__ . ' failed due to race condition for {key}.',
 374                                 [ 'key' => $key ]
 375                         );
 376
 377                         $success = false; // mismatched or failed
 378                 }
 379
 380                 $this->unlock( $key );
 381
 382                 return $success;
 383         }
 384
 385         /**
 386          * Change the expiration on a key if it exists
 387          *
 388          * If an expiry in the past is given then the key will immediately be expired
 389          *
 390          * @param string $key
 391          * @param int $expiry TTL or UNIX timestamp
 392          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 393          * @return bool Success Returns false on failure or if the item does not exist
 394          * @since 1.28
 395          */
 396         public function changeTTL( $key, $expiry = 0, $flags = 0 ) {
 397                 $found = false;
 398
 399                 $ok = $this->merge(
 400                         $key,
 401                         function ( $cache, $ttl, $currentValue ) use ( &$found ) {
 402                                 $found = ( $currentValue !== false );
 403
 404                                 return $currentValue; // nothing is written if this is false
 405                         },
 406                         $expiry,
 407                         1, // 1 attempt
 408                         $flags
 409                 );
 410
 411                 return ( $ok && $found );
 412         }
 413
 414         /**
 415          * Acquire an advisory lock on a key string
 416          *
 417          * Note that if reentry is enabled, duplicate calls ignore $expiry
 418          *
 419          * @param string $key
 420          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 421          * @param int $expiry Lock expiry [optional]; 1 day maximum
 422          * @param string $rclass Allow reentry if set and the current lock used this value
 423          * @return bool Success
 424          */
 425         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 426                 // Avoid deadlocks and allow lock reentry if specified
 427                 if ( isset( $this->locks[$key] ) ) {
 428                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 429                                 ++$this->locks[$key]['depth'];
 430                                 return true;
 431                         } else {
 432                                 return false;
 433                         }
 434                 }
 435
 436                 $fname = __METHOD__;
 437                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 438                 $loop = new WaitConditionLoop(
 439                         function () use ( $key, $expiry, $fname ) {
 440                                 $this->clearLastError();
 441                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 442                                         return WaitConditionLoop::CONDITION_REACHED; // locked!
 443                                 } elseif ( $this->getLastError() ) {
 444                                         $this->logger->warning(
 445                                                 $fname . ' failed due to I/O error for {key}.',
 446                                                 [ 'key' => $key ]
 447                                         );
 448
 449                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 450                                 }
 451
 452                                 return WaitConditionLoop::CONDITION_CONTINUE;
 453                         },
 454                         $timeout
 455                 );
 456
 457                 $code = $loop->invoke();
 458                 $locked = ( $code === $loop::CONDITION_REACHED );
 459                 if ( $locked ) {
 460                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 461                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 462                         $this->logger->warning(
 463                                 "$fname failed due to timeout for {key}.",
 464                                 [ 'key' => $key, 'timeout' => $timeout ]
 465                         );
 466                 }
 467
 468                 return $locked;
 469         }
 470
 471         /**
 472          * Release an advisory lock on a key string
 473          *
 474          * @param string $key
 475          * @return bool Success
 476          */
 477         public function unlock( $key ) {
 478                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 479                         unset( $this->locks[$key] );
 480
 481                         $ok = $this->delete( "{$key}:lock" );
 482                         if ( !$ok ) {
 483                                 $this->logger->warning(
 484                                         __METHOD__ . ' failed to release lock for {key}.',
 485                                         [ 'key' => $key ]
 486                                 );
 487                         }
 488
 489                         return $ok;
 490                 }
 491
 492                 return true;
 493         }
 494
 495         /**
 496          * Get a lightweight exclusive self-unlocking lock
 497          *
 498          * Note that the same lock cannot be acquired twice.
 499          *
 500          * This is useful for task de-duplication or to avoid obtrusive
 501          * (though non-corrupting) DB errors like INSERT key conflicts
 502          * or deadlocks when using LOCK IN SHARE MODE.
 503          *
 504          * @param string $key
 505          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 506          * @param int $expiry Lock expiry [optional]; 1 day maximum
 507          * @param string $rclass Allow reentry if set and the current lock used this value
 508          * @return ScopedCallback|null Returns null on failure
 509          * @since 1.26
 510          */
 511         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 512                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 513
 514                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 515                         return null;
 516                 }
 517
 518                 $lSince = $this->getCurrentTime(); // lock timestamp
 519
 520                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 521                         $latency = 0.050; // latency skew (err towards keeping lock present)
 522                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 523                         if ( ( $age + $latency ) >= $expiry ) {
 524                                 $this->logger->warning(
 525                                         "Lock for {key} held too long ({age} sec).",
 526                                         [ 'key' => $key, 'age' => $age ]
 527                                 );
 528                                 return; // expired; it's not "safe" to delete the key
 529                         }
 530                         $this->unlock( $key );
 531                 } );
 532         }
 533
 534         /**
 535          * Delete all objects expiring before a certain date.
 536          * @param string $date The reference date in MW format
 537          * @param callable|bool $progressCallback Optional, a function which will be called
 538          *     regularly during long-running operations with the percentage progress
 539          *     as the first parameter.
 540          *
 541          * @return bool Success, false if unimplemented
 542          */
 543         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 544                 // stub
 545                 return false;
 546         }
 547
 548         /**
 549          * Get an associative array containing the item for each of the keys that have items.
 550          * @param string[] $keys List of keys
 551          * @param int $flags Bitfield; supports READ_LATEST [optional]
 552          * @return array
 553          */
 554         public function getMulti( array $keys, $flags = 0 ) {
 555                 $res = [];
 556                 foreach ( $keys as $key ) {
 557                         $val = $this->get( $key, $flags );
 558                         if ( $val !== false ) {
 559                                 $res[$key] = $val;
 560                         }
 561                 }
 562
 563                 return $res;
 564         }
 565
 566         /**
 567          * Batch insertion/replace
 568          * @param mixed[] $data Map of (key => value)
 569          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 570          * @param int $flags Bitfield of BagOStuff::WRITE_* constants (since 1.33)
 571          * @return bool Success
 572          * @since 1.24
 573          */
 574         public function setMulti( array $data, $exptime = 0, $flags = 0 ) {
 575                 $res = true;
 576                 foreach ( $data as $key => $value ) {
 577                         if ( !$this->set( $key, $value, $exptime, $flags ) ) {
 578                                 $res = false;
 579                         }
 580                 }
 581
 582                 return $res;
 583         }
 584
 585         /**
 586          * Batch deletion
 587          * @param string[] $keys List of keys
 588          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 589          * @return bool Success
 590          * @since 1.33
 591          */
 592         public function deleteMulti( array $keys, $flags = 0 ) {
 593                 $res = true;
 594                 foreach ( $keys as $key ) {
 595                         $res = $this->delete( $key, $flags ) && $res;
 596                 }
 597
 598                 return $res;
 599         }
 600
 601         /**
 602          * Increase stored value of $key by $value while preserving its TTL
 603          * @param string $key Key to increase
 604          * @param int $value Value to add to $key (default: 1) [optional]
 605          * @return int|bool New value or false on failure
 606          */
 607         abstract public function incr( $key, $value = 1 );
 608
 609         /**
 610          * Decrease stored value of $key by $value while preserving its TTL
 611          * @param string $key
 612          * @param int $value Value to subtract from $key (default: 1) [optional]
 613          * @return int|bool New value or false on failure
 614          */
 615         public function decr( $key, $value = 1 ) {
 616                 return $this->incr( $key, - $value );
 617         }
 618
 619         /**
 620          * Increase stored value of $key by $value while preserving its TTL
 621          *
 622          * This will create the key with value $init and TTL $ttl instead if not present
 623          *
 624          * @param string $key
 625          * @param int $ttl
 626          * @param int $value
 627          * @param int $init
 628          * @return int|bool New value or false on failure
 629          * @since 1.24
 630          */
 631         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 632                 $this->clearLastError();
 633                 $newValue = $this->incr( $key, $value );
 634                 if ( $newValue === false && !$this->getLastError() ) {
 635                         // No key set; initialize
 636                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 637                         if ( $newValue === false && !$this->getLastError() ) {
 638                                 // Raced out initializing; increment
 639                                 $newValue = $this->incr( $key, $value );
 640                         }
 641                 }
 642
 643                 return $newValue;
 644         }
 645
 646         /**
 647          * Get the "last error" registered; clearLastError() should be called manually
 648          * @return int ERR_* constant for the "last error" registry
 649          * @since 1.23
 650          */
 651         public function getLastError() {
 652                 return $this->lastError;
 653         }
 654
 655         /**
 656          * Clear the "last error" registry
 657          * @since 1.23
 658          */
 659         public function clearLastError() {
 660                 $this->lastError = self::ERR_NONE;
 661         }
 662
 663         /**
 664          * Set the "last error" registry
 665          * @param int $err ERR_* constant
 666          * @since 1.23
 667          */
 668         protected function setLastError( $err ) {
 669                 $this->lastError = $err;
 670         }
 671
 672         /**
 673          * Let a callback be run to avoid wasting time on special blocking calls
 674          *
 675          * The callbacks may or may not be called ever, in any particular order.
 676          * They are likely to be invoked when something WRITE_SYNC is used used.
 677          * They should follow a caching pattern as shown below, so that any code
 678          * using the work will get it's result no matter what happens.
 679          * @code
 680          *     $result = null;
 681          *     $workCallback = function () use ( &$result ) {
 682          *         if ( !$result ) {
 683          *             $result = ....
 684          *         }
 685          *         return $result;
 686          *     }
 687          * @endcode
 688          *
 689          * @param callable $workCallback
 690          * @since 1.28
 691          */
 692         public function addBusyCallback( callable $workCallback ) {
 693                 $this->busyCallbacks[] = $workCallback;
 694         }
 695
 696         /**
 697          * @param string $text
 698          */
 699         protected function debug( $text ) {
 700                 if ( $this->debugMode ) {
 701                         $this->logger->debug( "{class} debug: $text", [
 702                                 'class' => static::class,
 703                         ] );
 704                 }
 705         }
 706
 707         /**
 708          * @param int $exptime
 709          * @return bool
 710          */
 711         protected function expiryIsRelative( $exptime ) {
 712                 return ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) );
 713         }
 714
 715         /**
 716          * Convert an optionally relative time to an absolute time
 717          * @param int $exptime
 718          * @return int
 719          */
 720         protected function convertToExpiry( $exptime ) {
 721                 if ( $this->expiryIsRelative( $exptime ) ) {
 722                         return (int)$this->getCurrentTime() + $exptime;
 723                 } else {
 724                         return $exptime;
 725                 }
 726         }
 727
 728         /**
 729          * Convert an optionally absolute expiry time to a relative time. If an
 730          * absolute time is specified which is in the past, use a short expiry time.
 731          *
 732          * @param int $exptime
 733          * @return int
 734          */
 735         protected function convertToRelative( $exptime ) {
 736                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 737                         $exptime -= (int)$this->getCurrentTime();
 738                         if ( $exptime <= 0 ) {
 739                                 $exptime = 1;
 740                         }
 741                         return $exptime;
 742                 } else {
 743                         return $exptime;
 744                 }
 745         }
 746
 747         /**
 748          * Check if a value is an integer
 749          *
 750          * @param mixed $value
 751          * @return bool
 752          */
 753         protected function isInteger( $value ) {
 754                 return ( is_int( $value ) || ctype_digit( $value ) );
 755         }
 756
 757         /**
 758          * Construct a cache key.
 759          *
 760          * @since 1.27
 761          * @param string $keyspace
 762          * @param array $args
 763          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 764          */
 765         public function makeKeyInternal( $keyspace, $args ) {
 766                 $key = $keyspace;
 767                 foreach ( $args as $arg ) {
 768                         $key .= ':' . str_replace( ':', '%3A', $arg );
 769                 }
 770                 return strtr( $key, ' ', '_' );
 771         }
 772
 773         /**
 774          * Make a global cache key.
 775          *
 776          * @since 1.27
 777          * @param string $class Key class
 778          * @param string|null $component [optional] Key component (starting with a key collection name)
 779          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 780          */
 781         public function makeGlobalKey( $class, $component = null ) {
 782                 return $this->makeKeyInternal( 'global', func_get_args() );
 783         }
 784
 785         /**
 786          * Make a cache key, scoped to this instance's keyspace.
 787          *
 788          * @since 1.27
 789          * @param string $class Key class
 790          * @param string|null $component [optional] Key component (starting with a key collection name)
 791          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 792          */
 793         public function makeKey( $class, $component = null ) {
 794                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 795         }
 796
 797         /**
 798          * @param int $flag ATTR_* class constant
 799          * @return int QOS_* class constant
 800          * @since 1.28
 801          */
 802         public function getQoS( $flag ) {
 803                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 804         }
 805
 806         /**
 807          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 808          *
 809          * @param BagOStuff[] $bags
 810          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 811          */
 812         protected function mergeFlagMaps( array $bags ) {
 813                 $map = [];
 814                 foreach ( $bags as $bag ) {
 815                         foreach ( $bag->attrMap as $attr => $rank ) {
 816                                 if ( isset( $map[$attr] ) ) {
 817                                         $map[$attr] = min( $map[$attr], $rank );
 818                                 } else {
 819                                         $map[$attr] = $rank;
 820                                 }
 821                         }
 822                 }
 823
 824                 return $map;
 825         }
 826
 827         /**
 828          * @return float UNIX timestamp
 829          * @codeCoverageIgnore
 830          */
 831         protected function getCurrentTime() {
 832                 return $this->wallClockOverride ?: microtime( true );
 833         }
 834
 835         /**
 836          * @param float|null &$time Mock UNIX timestamp for testing
 837          * @codeCoverageIgnore
 838          */
 839         public function setMockTime( &$time ) {
 840                 $this->wallClockOverride =& $time;
 841         }
 842 }