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 callback|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 int[] Map of (ATTR_* class constant => QOS_* class constant) */
  85         protected $attrMap = [];
  86
  87         /** Possible values for getLastError() */
  88         const ERR_NONE = 0; // no error
  89         const ERR_NO_RESPONSE = 1; // no response
  90         const ERR_UNREACHABLE = 2; // can't connect
  91         const ERR_UNEXPECTED = 3; // response gave some error
  92
  93         /** Bitfield constants for get()/getMulti() */
  94         const READ_LATEST = 1; // use latest data for replicated stores
  95         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  96         /** Bitfield constants for set()/merge() */
  97         const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
  98         const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache
  99
 100         /**
 101          * $params include:
 102          *   - logger: Psr\Log\LoggerInterface instance
 103          *   - keyspace: Default keyspace for $this->makeKey()
 104          *   - asyncHandler: Callable to use for scheduling tasks after the web request ends.
 105          *      In CLI mode, it should run the task immediately.
 106          *   - reportDupes: Whether to emit warning log messages for all keys that were
 107          *      requested more than once (requires an asyncHandler).
 108          *   - syncTimeout: How long to wait with WRITE_SYNC in seconds.
 109          * @param array $params
 110          */
 111         public function __construct( array $params = [] ) {
 112                 if ( isset( $params['logger'] ) ) {
 113                         $this->setLogger( $params['logger'] );
 114                 } else {
 115                         $this->setLogger( new NullLogger() );
 116                 }
 117
 118                 if ( isset( $params['keyspace'] ) ) {
 119                         $this->keyspace = $params['keyspace'];
 120                 }
 121
 122                 $this->asyncHandler = $params['asyncHandler'] ?? null;
 123
 124                 if ( !empty( $params['reportDupes'] ) && is_callable( $this->asyncHandler ) ) {
 125                         $this->reportDupes = true;
 126                 }
 127
 128                 $this->syncTimeout = $params['syncTimeout'] ?? 3;
 129         }
 130
 131         /**
 132          * @param LoggerInterface $logger
 133          * @return null
 134          */
 135         public function setLogger( LoggerInterface $logger ) {
 136                 $this->logger = $logger;
 137         }
 138
 139         /**
 140          * @param bool $bool
 141          */
 142         public function setDebug( $bool ) {
 143                 $this->debugMode = $bool;
 144         }
 145
 146         /**
 147          * Get an item with the given key, regenerating and setting it if not found
 148          *
 149          * If the callback returns false, then nothing is stored.
 150          *
 151          * @param string $key
 152          * @param int $ttl Time-to-live (seconds)
 153          * @param callable $callback Callback that derives the new value
 154          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 155          * @return mixed The cached value if found or the result of $callback otherwise
 156          * @since 1.27
 157          */
 158         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 159                 $value = $this->get( $key, $flags );
 160
 161                 if ( $value === false ) {
 162                         if ( !is_callable( $callback ) ) {
 163                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 164                         }
 165                         $value = call_user_func( $callback );
 166                         if ( $value !== false ) {
 167                                 $this->set( $key, $value, $ttl );
 168                         }
 169                 }
 170
 171                 return $value;
 172         }
 173
 174         /**
 175          * Get an item with the given key
 176          *
 177          * If the key includes a deterministic input hash (e.g. the key can only have
 178          * the correct value) or complete staleness checks are handled by the caller
 179          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 180          * This lets tiered backends know they can safely upgrade a cached value to
 181          * higher tiers using standard TTLs.
 182          *
 183          * @param string $key
 184          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 185          * @param int $oldFlags [unused]
 186          * @return mixed Returns false on failure and if the item does not exist
 187          */
 188         public function get( $key, $flags = 0, $oldFlags = null ) {
 189                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 190                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 191
 192                 $this->trackDuplicateKeys( $key );
 193
 194                 return $this->doGet( $key, $flags );
 195         }
 196
 197         /**
 198          * Track the number of times that a given key has been used.
 199          * @param string $key
 200          */
 201         private function trackDuplicateKeys( $key ) {
 202                 if ( !$this->reportDupes ) {
 203                         return;
 204                 }
 205
 206                 if ( !isset( $this->duplicateKeyLookups[$key] ) ) {
 207                         // Track that we have seen this key. This N-1 counting style allows
 208                         // easy filtering with array_filter() later.
 209                         $this->duplicateKeyLookups[$key] = 0;
 210                 } else {
 211                         $this->duplicateKeyLookups[$key] += 1;
 212
 213                         if ( $this->dupeTrackScheduled === false ) {
 214                                 $this->dupeTrackScheduled = true;
 215                                 // Schedule a callback that logs keys processed more than once by get().
 216                                 call_user_func( $this->asyncHandler, function () {
 217                                         $dups = array_filter( $this->duplicateKeyLookups );
 218                                         foreach ( $dups as $key => $count ) {
 219                                                 $this->logger->warning(
 220                                                         'Duplicate get(): "{key}" fetched {count} times',
 221                                                         // Count is N-1 of the actual lookup count
 222                                                         [ 'key' => $key, 'count' => $count + 1, ]
 223                                                 );
 224                                         }
 225                                 } );
 226                         }
 227                 }
 228         }
 229
 230         /**
 231          * @param string $key
 232          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 233          * @return mixed Returns false on failure and if the item does not exist
 234          */
 235         abstract protected function doGet( $key, $flags = 0 );
 236
 237         /**
 238          * @note: This method is only needed if merge() uses mergeViaCas()
 239          *
 240          * @param string $key
 241          * @param mixed &$casToken
 242          * @param int $flags Bitfield of BagOStuff::READ_* constants [optional]
 243          * @return mixed Returns false on failure and if the item does not exist
 244          * @throws Exception
 245          */
 246         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 247                 throw new Exception( __METHOD__ . ' not implemented.' );
 248         }
 249
 250         /**
 251          * Set an item
 252          *
 253          * @param string $key
 254          * @param mixed $value
 255          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 256          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 257          * @return bool Success
 258          */
 259         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 260
 261         /**
 262          * Delete an item
 263          *
 264          * @param string $key
 265          * @return bool True if the item was deleted or not found, false on failure
 266          */
 267         abstract public function delete( $key );
 268
 269         /**
 270          * Merge changes into the existing cache value (possibly creating a new one)
 271          *
 272          * The callback function returns the new value given the current value
 273          * (which will be false if not present), and takes the arguments:
 274          * (this BagOStuff, cache key, current value, TTL).
 275          * The TTL parameter is reference set to $exptime. It can be overriden in the callback.
 276          *
 277          * @param string $key
 278          * @param callable $callback Callback method to be executed
 279          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 280          * @param int $attempts The amount of times to attempt a merge in case of failure
 281          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 282          * @return bool Success
 283          * @throws InvalidArgumentException
 284          */
 285         public function merge( $key, callable $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 286                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 287         }
 288
 289         /**
 290          * @see BagOStuff::merge()
 291          *
 292          * @param string $key
 293          * @param callable $callback Callback method to be executed
 294          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 295          * @param int $attempts The amount of times to attempt a merge in case of failure
 296          * @return bool Success
 297          */
 298         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 299                 do {
 300                         $this->clearLastError();
 301                         $reportDupes = $this->reportDupes;
 302                         $this->reportDupes = false;
 303                         $casToken = null; // passed by reference
 304                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 305                         $this->reportDupes = $reportDupes;
 306
 307                         if ( $this->getLastError() ) {
 308                                 return false; // don't spam retries (retry only on races)
 309                         }
 310
 311                         // Derive the new value from the old value
 312                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 313
 314                         $this->clearLastError();
 315                         if ( $value === false ) {
 316                                 $success = true; // do nothing
 317                         } elseif ( $currentValue === false ) {
 318                                 // Try to create the key, failing if it gets created in the meantime
 319                                 $success = $this->add( $key, $value, $exptime );
 320                         } else {
 321                                 // Try to update the key, failing if it gets changed in the meantime
 322                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 323                         }
 324                         if ( $this->getLastError() ) {
 325                                 return false; // IO error; don't spam retries
 326                         }
 327                 } while ( !$success && --$attempts );
 328
 329                 return $success;
 330         }
 331
 332         /**
 333          * Check and set an item
 334          *
 335          * @param mixed $casToken
 336          * @param string $key
 337          * @param mixed $value
 338          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 339          * @return bool Success
 340          * @throws Exception
 341          */
 342         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 343                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 344         }
 345
 346         /**
 347          * @see BagOStuff::merge()
 348          *
 349          * @param string $key
 350          * @param callable $callback Callback method to be executed
 351          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 352          * @param int $attempts The amount of times to attempt a merge in case of failure
 353          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 354          * @return bool Success
 355          */
 356         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 357                 if ( !$this->lock( $key, 6 ) ) {
 358                         return false;
 359                 }
 360
 361                 $this->clearLastError();
 362                 $reportDupes = $this->reportDupes;
 363                 $this->reportDupes = false;
 364                 $currentValue = $this->get( $key, self::READ_LATEST );
 365                 $this->reportDupes = $reportDupes;
 366
 367                 if ( $this->getLastError() ) {
 368                         $success = false;
 369                 } else {
 370                         // Derive the new value from the old value
 371                         $value = call_user_func( $callback, $this, $key, $currentValue, $exptime );
 372                         if ( $value === false ) {
 373                                 $success = true; // do nothing
 374                         } else {
 375                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 376                         }
 377                 }
 378
 379                 if ( !$this->unlock( $key ) ) {
 380                         // this should never happen
 381                         trigger_error( "Could not release lock for key '$key'." );
 382                 }
 383
 384                 return $success;
 385         }
 386
 387         /**
 388          * Reset the TTL on a key if it exists
 389          *
 390          * @param string $key
 391          * @param int $expiry
 392          * @return bool Success Returns false if there is no key
 393          * @since 1.28
 394          */
 395         public function changeTTL( $key, $expiry = 0 ) {
 396                 $value = $this->get( $key );
 397
 398                 return ( $value === false ) ? false : $this->set( $key, $value, $expiry );
 399         }
 400
 401         /**
 402          * Acquire an advisory lock on a key string
 403          *
 404          * Note that if reentry is enabled, duplicate calls ignore $expiry
 405          *
 406          * @param string $key
 407          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 408          * @param int $expiry Lock expiry [optional]; 1 day maximum
 409          * @param string $rclass Allow reentry if set and the current lock used this value
 410          * @return bool Success
 411          */
 412         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 413                 // Avoid deadlocks and allow lock reentry if specified
 414                 if ( isset( $this->locks[$key] ) ) {
 415                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 416                                 ++$this->locks[$key]['depth'];
 417                                 return true;
 418                         } else {
 419                                 return false;
 420                         }
 421                 }
 422
 423                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 424                 $loop = new WaitConditionLoop(
 425                         function () use ( $key, $timeout, $expiry ) {
 426                                 $this->clearLastError();
 427                                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 428                                         return true; // locked!
 429                                 } elseif ( $this->getLastError() ) {
 430                                         return WaitConditionLoop::CONDITION_ABORTED; // network partition?
 431                                 }
 432
 433                                 return WaitConditionLoop::CONDITION_CONTINUE;
 434                         },
 435                         $timeout
 436                 );
 437
 438                 $locked = ( $loop->invoke() === $loop::CONDITION_REACHED );
 439                 if ( $locked ) {
 440                         $this->locks[$key] = [ 'class' => $rclass, 'depth' => 1 ];
 441                 }
 442
 443                 return $locked;
 444         }
 445
 446         /**
 447          * Release an advisory lock on a key string
 448          *
 449          * @param string $key
 450          * @return bool Success
 451          */
 452         public function unlock( $key ) {
 453                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 454                         unset( $this->locks[$key] );
 455
 456                         return $this->delete( "{$key}:lock" );
 457                 }
 458
 459                 return true;
 460         }
 461
 462         /**
 463          * Get a lightweight exclusive self-unlocking lock
 464          *
 465          * Note that the same lock cannot be acquired twice.
 466          *
 467          * This is useful for task de-duplication or to avoid obtrusive
 468          * (though non-corrupting) DB errors like INSERT key conflicts
 469          * or deadlocks when using LOCK IN SHARE MODE.
 470          *
 471          * @param string $key
 472          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 473          * @param int $expiry Lock expiry [optional]; 1 day maximum
 474          * @param string $rclass Allow reentry if set and the current lock used this value
 475          * @return ScopedCallback|null Returns null on failure
 476          * @since 1.26
 477          */
 478         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 479                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 480
 481                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 482                         return null;
 483                 }
 484
 485                 $lSince = microtime( true ); // lock timestamp
 486
 487                 return new ScopedCallback( function () use ( $key, $lSince, $expiry ) {
 488                         $latency = 0.050; // latency skew (err towards keeping lock present)
 489                         $age = ( microtime( true ) - $lSince + $latency );
 490                         if ( ( $age + $latency ) >= $expiry ) {
 491                                 $this->logger->warning( "Lock for $key held too long ($age sec)." );
 492                                 return; // expired; it's not "safe" to delete the key
 493                         }
 494                         $this->unlock( $key );
 495                 } );
 496         }
 497
 498         /**
 499          * Delete all objects expiring before a certain date.
 500          * @param string $date The reference date in MW format
 501          * @param callable|bool $progressCallback Optional, a function which will be called
 502          *     regularly during long-running operations with the percentage progress
 503          *     as the first parameter.
 504          *
 505          * @return bool Success, false if unimplemented
 506          */
 507         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 508                 // stub
 509                 return false;
 510         }
 511
 512         /**
 513          * Get an associative array containing the item for each of the keys that have items.
 514          * @param array $keys List of strings
 515          * @param int $flags Bitfield; supports READ_LATEST [optional]
 516          * @return array
 517          */
 518         public function getMulti( array $keys, $flags = 0 ) {
 519                 $res = [];
 520                 foreach ( $keys as $key ) {
 521                         $val = $this->get( $key );
 522                         if ( $val !== false ) {
 523                                 $res[$key] = $val;
 524                         }
 525                 }
 526                 return $res;
 527         }
 528
 529         /**
 530          * Batch insertion
 531          * @param array $data $key => $value assoc array
 532          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 533          * @return bool Success
 534          * @since 1.24
 535          */
 536         public function setMulti( array $data, $exptime = 0 ) {
 537                 $res = true;
 538                 foreach ( $data as $key => $value ) {
 539                         if ( !$this->set( $key, $value, $exptime ) ) {
 540                                 $res = false;
 541                         }
 542                 }
 543                 return $res;
 544         }
 545
 546         /**
 547          * @param string $key
 548          * @param mixed $value
 549          * @param int $exptime
 550          * @return bool Success
 551          */
 552         public function add( $key, $value, $exptime = 0 ) {
 553                 if ( $this->get( $key ) === false ) {
 554                         return $this->set( $key, $value, $exptime );
 555                 }
 556                 return false; // key already set
 557         }
 558
 559         /**
 560          * Increase stored value of $key by $value while preserving its TTL
 561          * @param string $key Key to increase
 562          * @param int $value Value to add to $key (Default 1)
 563          * @return int|bool New value or false on failure
 564          */
 565         public function incr( $key, $value = 1 ) {
 566                 if ( !$this->lock( $key ) ) {
 567                         return false;
 568                 }
 569                 $n = $this->get( $key );
 570                 if ( $this->isInteger( $n ) ) { // key exists?
 571                         $n += intval( $value );
 572                         $this->set( $key, max( 0, $n ) ); // exptime?
 573                 } else {
 574                         $n = false;
 575                 }
 576                 $this->unlock( $key );
 577
 578                 return $n;
 579         }
 580
 581         /**
 582          * Decrease stored value of $key by $value while preserving its TTL
 583          * @param string $key
 584          * @param int $value
 585          * @return int|bool New value or false on failure
 586          */
 587         public function decr( $key, $value = 1 ) {
 588                 return $this->incr( $key, - $value );
 589         }
 590
 591         /**
 592          * Increase stored value of $key by $value while preserving its TTL
 593          *
 594          * This will create the key with value $init and TTL $ttl instead if not present
 595          *
 596          * @param string $key
 597          * @param int $ttl
 598          * @param int $value
 599          * @param int $init
 600          * @return int|bool New value or false on failure
 601          * @since 1.24
 602          */
 603         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 604                 $newValue = $this->incr( $key, $value );
 605                 if ( $newValue === false ) {
 606                         // No key set; initialize
 607                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 608                 }
 609                 if ( $newValue === false ) {
 610                         // Raced out initializing; increment
 611                         $newValue = $this->incr( $key, $value );
 612                 }
 613
 614                 return $newValue;
 615         }
 616
 617         /**
 618          * Get the "last error" registered; clearLastError() should be called manually
 619          * @return int ERR_* constant for the "last error" registry
 620          * @since 1.23
 621          */
 622         public function getLastError() {
 623                 return $this->lastError;
 624         }
 625
 626         /**
 627          * Clear the "last error" registry
 628          * @since 1.23
 629          */
 630         public function clearLastError() {
 631                 $this->lastError = self::ERR_NONE;
 632         }
 633
 634         /**
 635          * Set the "last error" registry
 636          * @param int $err ERR_* constant
 637          * @since 1.23
 638          */
 639         protected function setLastError( $err ) {
 640                 $this->lastError = $err;
 641         }
 642
 643         /**
 644          * Let a callback be run to avoid wasting time on special blocking calls
 645          *
 646          * The callbacks may or may not be called ever, in any particular order.
 647          * They are likely to be invoked when something WRITE_SYNC is used used.
 648          * They should follow a caching pattern as shown below, so that any code
 649          * using the word will get it's result no matter what happens.
 650          * @code
 651          *     $result = null;
 652          *     $workCallback = function () use ( &$result ) {
 653          *         if ( !$result ) {
 654          *             $result = ....
 655          *         }
 656          *         return $result;
 657          *     }
 658          * @endcode
 659          *
 660          * @param callable $workCallback
 661          * @since 1.28
 662          */
 663         public function addBusyCallback( callable $workCallback ) {
 664                 $this->busyCallbacks[] = $workCallback;
 665         }
 666
 667         /**
 668          * Modify a cache update operation array for EventRelayer::notify()
 669          *
 670          * This is used for relayed writes, e.g. for broadcasting a change
 671          * to multiple data-centers. If the array contains a 'val' field
 672          * then the command involves setting a key to that value. Note that
 673          * for simplicity, 'val' is always a simple scalar value. This method
 674          * is used to possibly serialize the value and add any cache-specific
 675          * key/values needed for the relayer daemon (e.g. memcached flags).
 676          *
 677          * @param array $event
 678          * @return array
 679          * @since 1.26
 680          */
 681         public function modifySimpleRelayEvent( array $event ) {
 682                 return $event;
 683         }
 684
 685         /**
 686          * @param string $text
 687          */
 688         protected function debug( $text ) {
 689                 if ( $this->debugMode ) {
 690                         $this->logger->debug( "{class} debug: $text", [
 691                                 'class' => static::class,
 692                         ] );
 693                 }
 694         }
 695
 696         /**
 697          * Convert an optionally relative time to an absolute time
 698          * @param int $exptime
 699          * @return int
 700          */
 701         protected function convertExpiry( $exptime ) {
 702                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 703                         return time() + $exptime;
 704                 } else {
 705                         return $exptime;
 706                 }
 707         }
 708
 709         /**
 710          * Convert an optionally absolute expiry time to a relative time. If an
 711          * absolute time is specified which is in the past, use a short expiry time.
 712          *
 713          * @param int $exptime
 714          * @return int
 715          */
 716         protected function convertToRelative( $exptime ) {
 717                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 718                         $exptime -= time();
 719                         if ( $exptime <= 0 ) {
 720                                 $exptime = 1;
 721                         }
 722                         return $exptime;
 723                 } else {
 724                         return $exptime;
 725                 }
 726         }
 727
 728         /**
 729          * Check if a value is an integer
 730          *
 731          * @param mixed $value
 732          * @return bool
 733          */
 734         protected function isInteger( $value ) {
 735                 return ( is_int( $value ) || ctype_digit( $value ) );
 736         }
 737
 738         /**
 739          * Construct a cache key.
 740          *
 741          * @since 1.27
 742          * @param string $keyspace
 743          * @param array $args
 744          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 745          */
 746         public function makeKeyInternal( $keyspace, $args ) {
 747                 $key = $keyspace;
 748                 foreach ( $args as $arg ) {
 749                         $arg = str_replace( ':', '%3A', $arg );
 750                         $key = $key . ':' . $arg;
 751                 }
 752                 return strtr( $key, ' ', '_' );
 753         }
 754
 755         /**
 756          * Make a global cache key.
 757          *
 758          * @since 1.27
 759          * @param string $class Key class
 760          * @param string $component [optional] Key component (starting with a key collection name)
 761          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 762          */
 763         public function makeGlobalKey( $class, $component = null ) {
 764                 return $this->makeKeyInternal( 'global', func_get_args() );
 765         }
 766
 767         /**
 768          * Make a cache key, scoped to this instance's keyspace.
 769          *
 770          * @since 1.27
 771          * @param string $class Key class
 772          * @param string $component [optional] Key component (starting with a key collection name)
 773          * @return string Colon-delimited list of $keyspace followed by escaped components of $args
 774          */
 775         public function makeKey( $class, $component = null ) {
 776                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 777         }
 778
 779         /**
 780          * @param int $flag ATTR_* class constant
 781          * @return int QOS_* class constant
 782          * @since 1.28
 783          */
 784         public function getQoS( $flag ) {
 785                 return $this->attrMap[$flag] ?? self::QOS_UNKNOWN;
 786         }
 787
 788         /**
 789          * Merge the flag maps of one or more BagOStuff objects into a "lowest common denominator" map
 790          *
 791          * @param BagOStuff[] $bags
 792          * @return int[] Resulting flag map (class ATTR_* constant => class QOS_* constant)
 793          */
 794         protected function mergeFlagMaps( array $bags ) {
 795                 $map = [];
 796                 foreach ( $bags as $bag ) {
 797                         foreach ( $bag->attrMap as $attr => $rank ) {
 798                                 if ( isset( $map[$attr] ) ) {
 799                                         $map[$attr] = min( $map[$attr], $rank );
 800                                 } else {
 801                                         $map[$attr] = $rank;
 802                                 }
 803                         }
 804                 }
 805
 806                 return $map;
 807         }
 808 }