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
  33 /**
  34  * interface is intended to be more or less compatible with
  35  * the PHP memcached client.
  36  *
  37  * backends for local hash array and SQL table included:
  38  * @code
  39  *   $bag = new HashBagOStuff();
  40  *   $bag = new SqlBagOStuff(); # connect to db first
  41  * @endcode
  42  *
  43  * @ingroup Cache
  44  */
  45 abstract class BagOStuff implements IExpiringStore, LoggerAwareInterface {
  46         /** @var array[] Lock tracking */
  47         protected $locks = array();
  48
  49         /** @var integer */
  50         protected $lastError = self::ERR_NONE;
  51
  52         /** @var string */
  53         protected $keyspace = 'local';
  54
  55         /** @var LoggerInterface */
  56         protected $logger;
  57
  58         /** @var bool */
  59         private $debugMode = false;
  60
  61         /** Possible values for getLastError() */
  62         const ERR_NONE = 0; // no error
  63         const ERR_NO_RESPONSE = 1; // no response
  64         const ERR_UNREACHABLE = 2; // can't connect
  65         const ERR_UNEXPECTED = 3; // response gave some error
  66
  67         /** Bitfield constants for get()/getMulti() */
  68         const READ_LATEST = 1; // use latest data for replicated stores
  69         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  70         /** Bitfield constants for set()/merge() */
  71         const WRITE_SYNC = 1; // synchronously write to all locations for replicated stores
  72         const WRITE_CACHE_ONLY = 2; // Only change state of the in-memory cache
  73
  74         public function __construct( array $params = array() ) {
  75                 if ( isset( $params['logger'] ) ) {
  76                         $this->setLogger( $params['logger'] );
  77                 } else {
  78                         $this->setLogger( new NullLogger() );
  79                 }
  80
  81                 if ( isset( $params['keyspace'] ) ) {
  82                         $this->keyspace = $params['keyspace'];
  83                 }
  84         }
  85
  86         /**
  87          * @param LoggerInterface $logger
  88          * @return null
  89          */
  90         public function setLogger( LoggerInterface $logger ) {
  91                 $this->logger = $logger;
  92         }
  93
  94         /**
  95          * @param bool $bool
  96          */
  97         public function setDebug( $bool ) {
  98                 $this->debugMode = $bool;
  99         }
 100
 101         /**
 102          * Get an item with the given key, regenerating and setting it if not found
 103          *
 104          * If the callback returns false, then nothing is stored.
 105          *
 106          * @param string $key
 107          * @param int $ttl Time-to-live (seconds)
 108          * @param callable $callback Callback that derives the new value
 109          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 110          * @return mixed The cached value if found or the result of $callback otherwise
 111          * @since 1.27
 112          */
 113         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 114                 $value = $this->get( $key, $flags );
 115
 116                 if ( $value === false ) {
 117                         if ( !is_callable( $callback ) ) {
 118                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 119                         }
 120                         $value = call_user_func( $callback );
 121                         if ( $value !== false ) {
 122                                 $this->set( $key, $value, $ttl );
 123                         }
 124                 }
 125
 126                 return $value;
 127         }
 128
 129         /**
 130          * Get an item with the given key
 131          *
 132          * If the key includes a determistic input hash (e.g. the key can only have
 133          * the correct value) or complete staleness checks are handled by the caller
 134          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 135          * This lets tiered backends know they can safely upgrade a cached value to
 136          * higher tiers using standard TTLs.
 137          *
 138          * @param string $key
 139          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 140          * @param integer $oldFlags [unused]
 141          * @return mixed Returns false on failure and if the item does not exist
 142          */
 143         public function get( $key, $flags = 0, $oldFlags = null ) {
 144                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 145                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 146
 147                 return $this->doGet( $key, $flags );
 148         }
 149
 150         /**
 151          * @param string $key
 152          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 153          * @return mixed Returns false on failure and if the item does not exist
 154          */
 155         abstract protected function doGet( $key, $flags = 0 );
 156
 157         /**
 158          * @note: This method is only needed if merge() uses mergeViaCas()
 159          *
 160          * @param string $key
 161          * @param mixed $casToken
 162          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 163          * @return mixed Returns false on failure and if the item does not exist
 164          * @throws Exception
 165          */
 166         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 167                 throw new Exception( __METHOD__ . ' not implemented.' );
 168         }
 169
 170         /**
 171          * Set an item
 172          *
 173          * @param string $key
 174          * @param mixed $value
 175          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 176          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 177          * @return bool Success
 178          */
 179         abstract public function set( $key, $value, $exptime = 0, $flags = 0 );
 180
 181         /**
 182          * Delete an item
 183          *
 184          * @param string $key
 185          * @return bool True if the item was deleted or not found, false on failure
 186          */
 187         abstract public function delete( $key );
 188
 189         /**
 190          * Merge changes into the existing cache value (possibly creating a new one).
 191          * The callback function returns the new value given the current value
 192          * (which will be false if not present), and takes the arguments:
 193          * (this BagOStuff, cache key, current value).
 194          *
 195          * @param string $key
 196          * @param callable $callback Callback method to be executed
 197          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 198          * @param int $attempts The amount of times to attempt a merge in case of failure
 199          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 200          * @return bool Success
 201          * @throws InvalidArgumentException
 202          */
 203         public function merge( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 204                 if ( !is_callable( $callback ) ) {
 205                         throw new InvalidArgumentException( "Got invalid callback." );
 206                 }
 207
 208                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts, $flags );
 209         }
 210
 211         /**
 212          * @see BagOStuff::merge()
 213          *
 214          * @param string $key
 215          * @param callable $callback Callback method to be executed
 216          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 217          * @param int $attempts The amount of times to attempt a merge in case of failure
 218          * @return bool Success
 219          */
 220         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 221                 do {
 222                         $this->clearLastError();
 223                         $casToken = null; // passed by reference
 224                         $currentValue = $this->getWithToken( $key, $casToken, self::READ_LATEST );
 225                         if ( $this->getLastError() ) {
 226                                 return false; // don't spam retries (retry only on races)
 227                         }
 228
 229                         // Derive the new value from the old value
 230                         $value = call_user_func( $callback, $this, $key, $currentValue );
 231
 232                         $this->clearLastError();
 233                         if ( $value === false ) {
 234                                 $success = true; // do nothing
 235                         } elseif ( $currentValue === false ) {
 236                                 // Try to create the key, failing if it gets created in the meantime
 237                                 $success = $this->add( $key, $value, $exptime );
 238                         } else {
 239                                 // Try to update the key, failing if it gets changed in the meantime
 240                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 241                         }
 242                         if ( $this->getLastError() ) {
 243                                 return false; // IO error; don't spam retries
 244                         }
 245                 } while ( !$success && --$attempts );
 246
 247                 return $success;
 248         }
 249
 250         /**
 251          * Check and set an item
 252          *
 253          * @param mixed $casToken
 254          * @param string $key
 255          * @param mixed $value
 256          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 257          * @return bool Success
 258          * @throws Exception
 259          */
 260         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 261                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 262         }
 263
 264         /**
 265          * @see BagOStuff::merge()
 266          *
 267          * @param string $key
 268          * @param callable $callback Callback method to be executed
 269          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 270          * @param int $attempts The amount of times to attempt a merge in case of failure
 271          * @param int $flags Bitfield of BagOStuff::WRITE_* constants
 272          * @return bool Success
 273          */
 274         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10, $flags = 0 ) {
 275                 if ( !$this->lock( $key, 6 ) ) {
 276                         return false;
 277                 }
 278
 279                 $this->clearLastError();
 280                 $currentValue = $this->get( $key, self::READ_LATEST );
 281                 if ( $this->getLastError() ) {
 282                         $success = false;
 283                 } else {
 284                         // Derive the new value from the old value
 285                         $value = call_user_func( $callback, $this, $key, $currentValue );
 286                         if ( $value === false ) {
 287                                 $success = true; // do nothing
 288                         } else {
 289                                 $success = $this->set( $key, $value, $exptime, $flags ); // set the new value
 290                         }
 291                 }
 292
 293                 if ( !$this->unlock( $key ) ) {
 294                         // this should never happen
 295                         trigger_error( "Could not release lock for key '$key'." );
 296                 }
 297
 298                 return $success;
 299         }
 300
 301         /**
 302          * Acquire an advisory lock on a key string
 303          *
 304          * Note that if reentry is enabled, duplicate calls ignore $expiry
 305          *
 306          * @param string $key
 307          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 308          * @param int $expiry Lock expiry [optional]; 1 day maximum
 309          * @param string $rclass Allow reentry if set and the current lock used this value
 310          * @return bool Success
 311          */
 312         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 313                 // Avoid deadlocks and allow lock reentry if specified
 314                 if ( isset( $this->locks[$key] ) ) {
 315                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 316                                 ++$this->locks[$key]['depth'];
 317                                 return true;
 318                         } else {
 319                                 return false;
 320                         }
 321                 }
 322
 323                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 324
 325                 $this->clearLastError();
 326                 $timestamp = microtime( true ); // starting UNIX timestamp
 327                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 328                         $locked = true;
 329                 } elseif ( $this->getLastError() || $timeout <= 0 ) {
 330                         $locked = false; // network partition or non-blocking
 331                 } else {
 332                         // Estimate the RTT (us); use 1ms minimum for sanity
 333                         $uRTT = max( 1e3, ceil( 1e6 * ( microtime( true ) - $timestamp ) ) );
 334                         $sleep = 2 * $uRTT; // rough time to do get()+set()
 335
 336                         $attempts = 0; // failed attempts
 337                         do {
 338                                 if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
 339                                         // Exponentially back off after failed attempts to avoid network spam.
 340                                         // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 341                                         $sleep *= 2;
 342                                 }
 343                                 usleep( $sleep ); // back off
 344                                 $this->clearLastError();
 345                                 $locked = $this->add( "{$key}:lock", 1, $expiry );
 346                                 if ( $this->getLastError() ) {
 347                                         $locked = false; // network partition
 348                                         break;
 349                                 }
 350                         } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 351                 }
 352
 353                 if ( $locked ) {
 354                         $this->locks[$key] = array( 'class' => $rclass, 'depth' => 1 );
 355                 }
 356
 357                 return $locked;
 358         }
 359
 360         /**
 361          * Release an advisory lock on a key string
 362          *
 363          * @param string $key
 364          * @return bool Success
 365          */
 366         public function unlock( $key ) {
 367                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 368                         unset( $this->locks[$key] );
 369
 370                         return $this->delete( "{$key}:lock" );
 371                 }
 372
 373                 return true;
 374         }
 375
 376         /**
 377          * Get a lightweight exclusive self-unlocking lock
 378          *
 379          * Note that the same lock cannot be acquired twice.
 380          *
 381          * This is useful for task de-duplication or to avoid obtrusive
 382          * (though non-corrupting) DB errors like INSERT key conflicts
 383          * or deadlocks when using LOCK IN SHARE MODE.
 384          *
 385          * @param string $key
 386          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 387          * @param int $expiry Lock expiry [optional]; 1 day maximum
 388          * @param string $rclass Allow reentry if set and the current lock used this value
 389          * @return ScopedCallback|null Returns null on failure
 390          * @since 1.26
 391          */
 392         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 393                 $expiry = min( $expiry ?: INF, self::TTL_DAY );
 394
 395                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 396                         return null;
 397                 }
 398
 399                 $lSince = microtime( true ); // lock timestamp
 400                 // PHP 5.3: Can't use $this in a closure
 401                 $that = $this;
 402                 $logger = $this->logger;
 403
 404                 return new ScopedCallback( function() use ( $that, $logger, $key, $lSince, $expiry ) {
 405                         $latency = .050; // latency skew (err towards keeping lock present)
 406                         $age = ( microtime( true ) - $lSince + $latency );
 407                         if ( ( $age + $latency ) >= $expiry ) {
 408                                 $logger->warning( "Lock for $key held too long ($age sec)." );
 409                                 return; // expired; it's not "safe" to delete the key
 410                         }
 411                         $that->unlock( $key );
 412                 } );
 413         }
 414
 415         /**
 416          * Delete all objects expiring before a certain date.
 417          * @param string $date The reference date in MW format
 418          * @param callable|bool $progressCallback Optional, a function which will be called
 419          *     regularly during long-running operations with the percentage progress
 420          *     as the first parameter.
 421          *
 422          * @return bool Success, false if unimplemented
 423          */
 424         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 425                 // stub
 426                 return false;
 427         }
 428
 429         /**
 430          * Get an associative array containing the item for each of the keys that have items.
 431          * @param array $keys List of strings
 432          * @param integer $flags Bitfield; supports READ_LATEST [optional]
 433          * @return array
 434          */
 435         public function getMulti( array $keys, $flags = 0 ) {
 436                 $res = array();
 437                 foreach ( $keys as $key ) {
 438                         $val = $this->get( $key );
 439                         if ( $val !== false ) {
 440                                 $res[$key] = $val;
 441                         }
 442                 }
 443                 return $res;
 444         }
 445
 446         /**
 447          * Batch insertion
 448          * @param array $data $key => $value assoc array
 449          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 450          * @return bool Success
 451          * @since 1.24
 452          */
 453         public function setMulti( array $data, $exptime = 0 ) {
 454                 $res = true;
 455                 foreach ( $data as $key => $value ) {
 456                         if ( !$this->set( $key, $value, $exptime ) ) {
 457                                 $res = false;
 458                         }
 459                 }
 460                 return $res;
 461         }
 462
 463         /**
 464          * @param string $key
 465          * @param mixed $value
 466          * @param int $exptime
 467          * @return bool Success
 468          */
 469         public function add( $key, $value, $exptime = 0 ) {
 470                 if ( $this->get( $key ) === false ) {
 471                         return $this->set( $key, $value, $exptime );
 472                 }
 473                 return false; // key already set
 474         }
 475
 476         /**
 477          * Increase stored value of $key by $value while preserving its TTL
 478          * @param string $key Key to increase
 479          * @param int $value Value to add to $key (Default 1)
 480          * @return int|bool New value or false on failure
 481          */
 482         public function incr( $key, $value = 1 ) {
 483                 if ( !$this->lock( $key ) ) {
 484                         return false;
 485                 }
 486                 $n = $this->get( $key );
 487                 if ( $this->isInteger( $n ) ) { // key exists?
 488                         $n += intval( $value );
 489                         $this->set( $key, max( 0, $n ) ); // exptime?
 490                 } else {
 491                         $n = false;
 492                 }
 493                 $this->unlock( $key );
 494
 495                 return $n;
 496         }
 497
 498         /**
 499          * Decrease stored value of $key by $value while preserving its TTL
 500          * @param string $key
 501          * @param int $value
 502          * @return int|bool New value or false on failure
 503          */
 504         public function decr( $key, $value = 1 ) {
 505                 return $this->incr( $key, - $value );
 506         }
 507
 508         /**
 509          * Increase stored value of $key by $value while preserving its TTL
 510          *
 511          * This will create the key with value $init and TTL $ttl instead if not present
 512          *
 513          * @param string $key
 514          * @param int $ttl
 515          * @param int $value
 516          * @param int $init
 517          * @return int|bool New value or false on failure
 518          * @since 1.24
 519          */
 520         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 521                 $newValue = $this->incr( $key, $value );
 522                 if ( $newValue === false ) {
 523                         // No key set; initialize
 524                         $newValue = $this->add( $key, (int)$init, $ttl ) ? $init : false;
 525                 }
 526                 if ( $newValue === false ) {
 527                         // Raced out initializing; increment
 528                         $newValue = $this->incr( $key, $value );
 529                 }
 530
 531                 return $newValue;
 532         }
 533
 534         /**
 535          * Get the "last error" registered; clearLastError() should be called manually
 536          * @return int ERR_* constant for the "last error" registry
 537          * @since 1.23
 538          */
 539         public function getLastError() {
 540                 return $this->lastError;
 541         }
 542
 543         /**
 544          * Clear the "last error" registry
 545          * @since 1.23
 546          */
 547         public function clearLastError() {
 548                 $this->lastError = self::ERR_NONE;
 549         }
 550
 551         /**
 552          * Set the "last error" registry
 553          * @param int $err ERR_* constant
 554          * @since 1.23
 555          */
 556         protected function setLastError( $err ) {
 557                 $this->lastError = $err;
 558         }
 559
 560         /**
 561          * Modify a cache update operation array for EventRelayer::notify()
 562          *
 563          * This is used for relayed writes, e.g. for broadcasting a change
 564          * to multiple data-centers. If the array contains a 'val' field
 565          * then the command involves setting a key to that value. Note that
 566          * for simplicity, 'val' is always a simple scalar value. This method
 567          * is used to possibly serialize the value and add any cache-specific
 568          * key/values needed for the relayer daemon (e.g. memcached flags).
 569          *
 570          * @param array $event
 571          * @return array
 572          * @since 1.26
 573          */
 574         public function modifySimpleRelayEvent( array $event ) {
 575                 return $event;
 576         }
 577
 578         /**
 579          * @param string $text
 580          */
 581         protected function debug( $text ) {
 582                 if ( $this->debugMode ) {
 583                         $this->logger->debug( "{class} debug: $text", array(
 584                                 'class' => get_class( $this ),
 585                         ) );
 586                 }
 587         }
 588
 589         /**
 590          * Convert an optionally relative time to an absolute time
 591          * @param int $exptime
 592          * @return int
 593          */
 594         protected function convertExpiry( $exptime ) {
 595                 if ( $exptime != 0 && $exptime < ( 10 * self::TTL_YEAR ) ) {
 596                         return time() + $exptime;
 597                 } else {
 598                         return $exptime;
 599                 }
 600         }
 601
 602         /**
 603          * Convert an optionally absolute expiry time to a relative time. If an
 604          * absolute time is specified which is in the past, use a short expiry time.
 605          *
 606          * @param int $exptime
 607          * @return int
 608          */
 609         protected function convertToRelative( $exptime ) {
 610                 if ( $exptime >= ( 10 * self::TTL_YEAR ) ) {
 611                         $exptime -= time();
 612                         if ( $exptime <= 0 ) {
 613                                 $exptime = 1;
 614                         }
 615                         return $exptime;
 616                 } else {
 617                         return $exptime;
 618                 }
 619         }
 620
 621         /**
 622          * Check if a value is an integer
 623          *
 624          * @param mixed $value
 625          * @return bool
 626          */
 627         protected function isInteger( $value ) {
 628                 return ( is_int( $value ) || ctype_digit( $value ) );
 629         }
 630
 631         /**
 632          * Construct a cache key.
 633          *
 634          * @since 1.27
 635          * @param string $keyspace
 636          * @param array $args
 637          * @return string
 638          */
 639         public function makeKeyInternal( $keyspace, $args ) {
 640                 $key = $keyspace;
 641                 foreach ( $args as $arg ) {
 642                         $arg = str_replace( ':', '%3A', $arg );
 643                         $key = $key . ':' . $arg;
 644                 }
 645                 return strtr( $key, ' ', '_' );
 646         }
 647
 648         /**
 649          * Make a global cache key.
 650          *
 651          * @since 1.27
 652          * @param string ... Key component (variadic)
 653          * @return string
 654          */
 655         public function makeGlobalKey() {
 656                 return $this->makeKeyInternal( 'global', func_get_args() );
 657         }
 658
 659         /**
 660          * Make a cache key, scoped to this instance's keyspace.
 661          *
 662          * @since 1.27
 663          * @param string ... Key component (variadic)
 664          * @return string
 665          */
 666         public function makeKey() {
 667                 return $this->makeKeyInternal( $this->keyspace, func_get_args() );
 668         }
 669 }