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 = 1; // synchronously write to all locations for replicated stores
  95         const WRITE_CACHE_ONLY = 2; // 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          * If the callback returns false, then nothing is stored.
 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_* 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 );
 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 and 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 and 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 and 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          *
 271          * @param string $key
 272          * @param callable $callback Callback method to be executed
 273          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 274          * @param int $attempts The amount of times to attempt a merge in case of failure
 275          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 276          * @return bool Success
 277          * @throws InvalidArgumentException
 278          */
 279         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 280                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 281         }
 282
 283         /**
 284          * @see BagOStuff::merge()
 285          *
 286          * @param string $key
 287          * @param callable $callback Callback method to be executed
 288          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 289          * @param int $attempts The amount of times to attempt a merge in case of failure
 290          * @return bool Success
 291          */
 292         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 293                 do {
 294                         $this->clearLastError();
 295                         $reportDupes = $this->reportDupes;
 296                         $this->reportDupes = false;
 297                         $casToken = null; // passed by reference
 298                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 299                         $this->reportDupes = $reportDupes;
 300
 301                         if ( $this->getLastError() ) {
 302                                 $this->logger->warning(
 303                                         __METHOD__ . ' failed due to I/O error on get() for {key}.',
 304                                         [ 'key' => $key ]
 305                                 );
 306
 307                                 return false; // don't spam retries (retry only on races)
 308                         }
 309
 310                         // Derive the new value from the old value
 311                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 312
 313                         $this->clearLastError();
 314                         if ( $value === false ) {
 315                                 $success = true; // do nothing
 316                         } elseif ( $currentValue === false ) {
 317                                 // Try to create the key, failing if it gets created in the meantime
 318                                 $success = $this->add( $key, $value, $exptime );
 319                         } else {
 320                                 // Try to update the key, failing if it gets changed in the meantime
 321                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 322                         }
 323                         if ( $this->getLastError() ) {
 324                                 $this->logger->warning(
 325                                         __METHOD__ . ' failed due to I/O error for {key}.',
 326                                         [ 'key' => $key ]
 327                                 );
 328
 329                                 return false; // IO error; don't spam retries
 330                         }
 331                 } while ( !$success && --$attempts );
 332
 333                 return $success;
 334         }
 335
 336         /**
 337          * Check and set an item
 338          *
 339          * @param mixed $casToken
 340          * @param string $key
 341          * @param mixed $value
 342          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 343          * @return bool Success
 344          * @throws Exception
 345          */
 346         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 347                 if ( !$this->lock( $key, 0 ) ) {
 348                         return false; // non-blocking
 349                 }
 350
 351                 $curCasToken = null; // passed by reference
 352                 $this->getWithToken( $key, $curCasToken, self::READ_LATEST );
 353                 if ( $casToken === $curCasToken ) {
 354                         $success = $this->set( $key, $value, $exptime );
 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          * @see BagOStuff::merge()
 371          *
 372          * @param string $key
 373          * @param callable $callback Callback method to be executed
 374          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 375          * @param int $attempts The amount of times to attempt a merge in case of failure
 376          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 377          * @return bool Success
 378          */
 379         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 380                 if ( $attempts <= 1 ) {
 381                         $timeout = 0; // clearly intended to be "non-blocking"
 382                 } else {
 383                         $timeout = 3;
 384                 }
 385
 386                 if ( !$this->lock( $key, $timeout ) ) {
 387                         return false;
 388                 }
 389
 390                 $this->clearLastError();
 391                 $reportDupes = $this->reportDupes;
 392                 $this->reportDupes = false;
 393                 $currentValue = $this->get( $key, self::READ_LATEST );
 394                 $this->reportDupes = $reportDupes;
 395
 396                 if ( $this->getLastError() ) {
 397                         $this->logger->warning(
 398                                 __METHOD__ . ' failed due to I/O error on get() for {key}.',
 399                                 [ 'key' => $key ]
 400                         );
 401
 402                         $success = false;
 403                 } else {
 404                         // Derive the new value from the old value
 405                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 406                         if ( $value === false ) {
 407                                 $success = true; // do nothing
 408                         } else {
 409                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 410                         }
 411                 }
 412
 413                 if ( !$this->unlock( $key ) ) {
 414                         // this should never happen
 415                         trigger_error( "Could not release lock for key '$key'." );
 416                 }
 417
 418                 return $success;
 419         }
 420
 421         /**
 422          * Reset the TTL on a key if it exists
 423          *
 424          * @param string $key
 425          * @param int $expiry
 426          * @return bool Success Returns false if there is no key
 427          * @since 1.28
 428          */
 429         public function changeTTL( $key, $expiry = 0 ) {
 430                 $value = $this->get( $key );
 431
 432                 return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
 433         }
 434
 435         /**
 436          * Acquire an advisory lock on a key string
 437          *
 438          * Note that if reentry is enabled, duplicate calls ignore $expiry
 439          *
 440          * @param string $key
 441          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 442          * @param int $expiry Lock expiry [optional]; 1 day maximum
 443          * @param string $rclass Allow reentry if set and the current lock used this value
 444          * @return bool Success
 445          */
 446         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 447                 // Avoid deadlocks and allow lock reentry if specified
 448                 if ( isset( $this->locks[$key] ) ) {
 449                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 450                                 ++$this->locks[$key]['depth'];
 451                                 return true;
 452                         } else {
 453                                 return false;
 454                         }
 455                 }
 456
 457                 $fname = __METHOD__;
 458                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 459                 $loop = new WaitConditionLoop(
 460                         function () use ( $key, $expiry, $fname ) {
 461                                 $this->clearLastError();
 462                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 463                                         return true; // locked!
 464                                 } elseif ( $this->getLastError() ) {
 465                                         $this->logger->warning(
 466                                                 $fname . ' failed due to I/O error for {key}.',
 467                                                 [ 'key' => $key ]
 468                                         );
 469
 470                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 471                                 }
 472
 473                                 return WaitConditionLoop::CONDITION_CONTINUE;
 474                         },
 475                         $timeout
 476                 );
 477
 478                 $code = $loop->invoke();
 479                 $locked = ( $code === $loop::CONDITION_REACHED );
 480                 if ( $locked ) {
 481                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 482                 } elseif ( $code === $loop::CONDITION_TIMED_OUT ) {
 483                         $this->logger->warning(
 484                                 "$fname failed due to timeout for {key}.",
 485                                 [ 'key' => $key, 'timeout' => $timeout ]
 486                         );
 487                 }
 488
 489                 return $locked;
 490         }
 491
 492         /**
 493          * Release an advisory lock on a key string
 494          *
 495          * @param string $key
 496          * @return bool Success
 497          */
 498         public function unlock( $key ) {
 499                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 500                         unset( $this->locks[$key] );
 501
 502                         $ok = $this->delete( "{$key}:lock" );
 503                         if ( !$ok ) {
 504                                 $this->logger->warning(
 505                                         __METHOD__ . ' failed to release lock for {key}.',
 506                                         [ 'key' => $key ]
 507                                 );
 508                         }
 509
 510                         return $ok;
 511                 }
 512
 513                 return true;
 514         }
 515
 516         /**
 517          * Get a lightweight exclusive self-unlocking lock
 518          *
 519          * Note that the same lock cannot be acquired twice.
 520          *
 521          * This is useful for task de-duplication or to avoid obtrusive
 522          * (though non-corrupting) DB errors like INSERT key conflicts
 523          * or deadlocks when using LOCK IN SHARE MODE.
 524          *
 525          * @param string $key
 526          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 527          * @param int $expiry Lock expiry [optional]; 1 day maximum
 528          * @param string $rclass Allow reentry if set and the current lock used this value
 529          * @return ScopedCallback|null Returns null on failure
 530          * @since 1.26
 531          */
 532         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 533                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 534
 535                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 536                         return null;
 537                 }
 538
 539                 $lSince = $this->getCurrentTime(); // lock timestamp
 540
 541                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 542                         $latency = 0.050; // latency skew (err towards keeping lock present)
 543                         $age = ( $this->getCurrentTime() - $lSince + $latency );
 544                         if ( ( $age + $latency ) >= $expiry ) {
 545                                 $this->logger->warning(
 546                                         "Lock for {key} held too long ({age} sec).",
 547                                         [ 'key' => $key, 'age' => $age ]
 548                                 );
 549                                 return; // expired; it's not "safe" to delete the key
 550                         }
 551                         $this->unlock( $key );
 552                 } );
 553         }
 554
 555         /**
 556          * Delete all objects expiring before a certain date.
 557          * @param string $date The reference date in MW format
 558          * @param callable|bool $progressCallback Optional, a function which will be called
 559          *     regularly during long-running operations with the percentage progress
 560          *     as the first parameter.
 561          *
 562          * @return bool Success, false if unimplemented
 563          */
 564         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 565                 // stub
 566                 return false;
 567         }
 568
 569         /**
 570          * Get an associative array containing the item for each of the keys that have items.
 571          * @param array $keys List of strings
 572          * @param int $flags Bitfield; supports READ_LATEST [optional]
 573          * @return array
 574          */
 575         public function getMulti( array $keys, $flags = 0 ) {
 576                 $res = [];
 577                 foreach ( $keys as $key ) {
 578                         $val = $this->get( $key );
 579                         if ( $val !== false ) {
 580                                 $res[$key] = $val;
 581                         }
 582                 }
 583                 return $res;
 584         }
 585
 586         /**
 587          * Batch insertion
 588          * @param array $data $key => $value assoc array
 589          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 590          * @return bool Success
 591          * @since 1.24
 592          */
 593         public function setMulti( array $data, $exptime = 0 ) {
 594                 $res = true;
 595                 foreach ( $data as $key => $value ) {
 596                         if ( !$this->set( $key, $value, $exptime ) ) {
 597                                 $res = false;
 598                         }
 599                 }
 600                 return $res;
 601         }
 602
 603         /**
 604          * @param string $key
 605          * @param mixed $value
 606          * @param int $exptime
 607          * @return bool Success
 608          */
 609         public function add( $key, $value, $exptime = 0 ) {
 610                 // @note: avoid lock() here since that method uses *this* method by default
 611                 if ( $this->get( $key ) === false ) {
 612                         return $this->set( $key, $value, $exptime );
 613                 }
 614                 return false; // key already set
 615         }
 616
 617         /**
 618          * Increase stored value of $key by $value while preserving its TTL
 619          * @param string $key Key to increase
 620          * @param int $value Value to add to $key (Default 1)
 621          * @return int|bool New value or false on failure
 622          */
 623         public function incr( $key, $value = 1 ) {
 624                 if ( !$this->lock( $key, 1 ) ) {
 625                         return false;
 626                 }
 627                 $n = $this->get( $key );
 628                 if ( $this->isInteger( $n ) ) { // key exists?
 629                         $n += intval( $value );
 630                         $this->set( $key, max( 0, $n ) ); // exptime?
 631                 } else {
 632                         $n = false;
 633                 }
 634                 $this->unlock( $key );
 635
 636                 return $n;
 637         }
 638
 639         /**
 640          * Decrease stored value of $key by $value while preserving its TTL
 641          * @param string $key
 642          * @param int $value
 643          * @return int|bool New value or false on failure
 644          */
 645         public function decr( $key, $value = 1 ) {
 646                 return $this->incr( $key, - $value );
 647         }
 648
 649         /**
 650          * Increase stored value of $key by $value while preserving its TTL
 651          *
 652          * This will create the key with value $init and TTL $ttl instead if not present
 653          *
 654          * @param string $key
 655          * @param int $ttl
 656          * @param int $value
 657          * @param int $init
 658          * @return int|bool New value or false on failure
 659          * @since 1.24
 660          */
 661         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 662                 $this->clearLastError();
 663                 $newValue = $this->incr( $key, $value );
 664                 if ( $newValue === false && !$this->getLastError() ) {
 665                         // No key set; initialize
 666                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 667                         if ( $newValue === false && !$this->getLastError() ) {
 668                                 // Raced out initializing; increment
 669                                 $newValue = $this->incr( $key, $value );
 670                         }
 671                 }
 672
 673                 return $newValue;
 674         }
 675
 676         /**
 677          * Get the "last error" registered; clearLastError() should be called manually
 678          * @return int ERR_* constant for the "last error" registry
 679          * @since 1.23
 680          */
 681         public function getLastError() {
 682                 return $this->lastError;
 683         }
 684
 685         /**
 686          * Clear the "last error" registry
 687          * @since 1.23
 688          */
 689         public function clearLastError() {
 690                 $this->lastError = self::ERR_NONE;
 691         }
 692
 693         /**
 694          * Set the "last error" registry
 695          * @param int $err ERR_* constant
 696          * @since 1.23
 697          */
 698         protected function setLastError( $err ) {
 699                 $this->lastError = $err;
 700         }
 701
 702         /**
 703          * Let a callback be run to avoid wasting time on special blocking calls
 704          *
 705          * The callbacks may or may not be called ever, in any particular order.
 706          * They are likely to be invoked when something WRITE_SYNC is used used.
 707          * They should follow a caching pattern as shown below, so that any code
 708          * using the work will get it's result no matter what happens.
 709          * @code
 710          *     $result = null;
 711          *     $workCallback = function () use ( &$result ) {
 712          *         if ( !$result ) {
 713          *             $result = ....
 714          *         }
 715          *         return $result;
 716          *     }
 717          * @endcode
 718          *
 719          * @param callable $workCallback
 720          * @since 1.28
 721          */
 722         public function addBusyCallback( callable $workCallback ) {
 723                 $this->busyCallbacks[] = $workCallback;
 724         }
 725
 726         /**
 727          * @param string $text
 728          */
 729         protected function debug( $text ) {
 730                 if ( $this->debugMode ) {
 731                         $this->logger->debug( "{class} debug: $text", [
 732                                 'class' => static::class,
 733                         ] );
 734                 }
 735         }
 736
 737         /**
 738          * Convert an optionally relative time to an absolute time
 739          * @param int $exptime
 740          * @return int
 741          */
 742         protected function convertExpiry( $exptime ) {
 743                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 744                         return (int)$this->getCurrentTime() + $exptime;
 745                 } else {
 746                         return $exptime;
 747                 }
 748         }
 749
 750         /**
 751          * Convert an optionally absolute expiry time to a relative time. If an
 752          * absolute time is specified which is in the past, use a short expiry time.
 753          *
 754          * @param int $exptime
 755          * @return int
 756          */
 757         protected function convertToRelative( $exptime ) {
 758                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 759                         $exptime -= (int)$this->getCurrentTime();
 760                         if ( $exptime <= 0 ) {
 761                                 $exptime = 1;
 762                         }
 763                         return $exptime;
 764                 } else {
 765                         return $exptime;
 766                 }
 767         }
 768
 769         /**
 770          * Check if a value is an integer
 771          *
 772          * @param mixed $value
 773          * @return bool
 774          */
 775         protected function isInteger( $value ) {
 776                 return ( is_int( $value ) || ctype_digit( $value ) );
 777         }
 778
 779         /**
 780          * Construct a cache key.
 781          *
 782          * @since 1.27
 783          * @param string $keyspace
 784          * @param array $args
 785          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 786          */
 787         public function makeKeyInternal( $keyspace, $args ) {
 788                 $key = $keyspace;
 789                 foreach ( $args as $arg ) {
 790                         $key .= ':' . str_replace( ':', '%3A', $arg );
 791                 }
 792                 return strtr( $key, ' ', '_' );
 793         }
 794
 795         /**
 796          * Make a global cache key.
 797          *
 798          * @since 1.27
 799          * @param string $class Key class
 800          * @param string|null $component [optional] Key component (starting with a key collection name)
 801          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 802          */
 803         public function makeGlobalKey( $class, $component = null ) {
 804                 return $this->makeKeyInternal( 'global', func_get_args() );
 805         }
 806
 807         /**
 808          * Make a cache key, scoped to this instance's keyspace.
 809          *
 810          * @since 1.27
 811          * @param string $class Key class
 812          * @param string|null $component [optional] Key component (starting with a key collection name)
 813          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 814          */
 815         public function makeKey( $class, $component = null ) {
 816                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 817         }
 818
 819         /**
 820          * @param int $flag ATTR_* class constant
 821          * @return int QOS_* class constant
 822          * @since 1.28
 823          */
 824         public function getQoS( $flag ) {
 825                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 826         }
 827
 828         /**
 829          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 830          *
 831          * @param BagOStuff[] $bags
 832          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 833          */
 834         protected function mergeFlagMaps( array $bags ) {
 835                 $map = [];
 836                 foreach ( $bags as $bag ) {
 837                         foreach ( $bag->attrMap as $attr => $rank ) {
 838                                 if ( isset( $map[$attr] ) ) {
 839                                         $map[$attr] = min( $map[$attr], $rank );
 840                                 } else {
 841                                         $map[$attr] = $rank;
 842                                 }
 843                         }
 844                 }
 845
 846                 return $map;
 847         }
 848
 849         /**
 850          * @return float UNIX timestamp
 851          * @codeCoverageIgnore
 852          */
 853         protected function getCurrentTime() {
 854                 return $this->wallClockOverride ?: microtime( true );
 855         }
 856
 857         /**
 858          * @param float|null &$time Mock UNIX timestamp for testing
 859          * @codeCoverageIgnore
 860          */
 861         public function setMockTime( &$time ) {
 862                 $this->wallClockOverride =& $time;
 863         }
 864 }