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 LoggerAwareInterface {
  46         /** @var array[] Lock tracking */
  47         protected $locks = array();
  48         /** @var integer */
  49         protected $lastError = self::ERR_NONE;
  50
  51         /** @var LoggerInterface */
  52         protected $logger;
  53
  54         /** @var bool */
  55         private $debugMode = false;
  56
  57         /** Possible values for getLastError() */
  58         const ERR_NONE = 0; // no error
  59         const ERR_NO_RESPONSE = 1; // no response
  60         const ERR_UNREACHABLE = 2; // can't connect
  61         const ERR_UNEXPECTED = 3; // response gave some error
  62
  63         /** Bitfield constants for get()/getMulti() */
  64         const READ_LATEST = 1; // use latest data for replicated stores
  65         const READ_VERIFIED = 2; // promise that caller can tell when keys are stale
  66
  67         public function __construct( array $params = array() ) {
  68                 if ( isset( $params['logger'] ) ) {
  69                         $this->setLogger( $params['logger'] );
  70                 } else {
  71                         $this->setLogger( new NullLogger() );
  72                 }
  73         }
  74
  75         /**
  76          * @param LoggerInterface $logger
  77          * @return null
  78          */
  79         public function setLogger( LoggerInterface $logger ) {
  80                 $this->logger = $logger;
  81         }
  82
  83         /**
  84          * @param bool $bool
  85          */
  86         public function setDebug( $bool ) {
  87                 $this->debugMode = $bool;
  88         }
  89
  90         /**
  91          * Get an item with the given key, regenerating and setting it if not found
  92          *
  93          * If the callback returns false, then nothing is stored.
  94          *
  95          * @param string $key
  96          * @param int $ttl Time-to-live (seconds)
  97          * @param callable $callback Callback that derives the new value
  98          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
  99          * @return mixed The cached value if found or the result of $callback otherwise
 100          * @since 1.27
 101          */
 102         final public function getWithSetCallback( $key, $ttl, $callback, $flags = 0 ) {
 103                 $value = $this->get( $key, $flags );
 104
 105                 if ( $value === false ) {
 106                         if ( !is_callable( $callback ) ) {
 107                                 throw new InvalidArgumentException( "Invalid cache miss callback provided." );
 108                         }
 109                         $value = call_user_func( $callback );
 110                         if ( $value !== false ) {
 111                                 $this->set( $key, $value, $ttl );
 112                         }
 113                 }
 114
 115                 return $value;
 116         }
 117
 118         /**
 119          * Get an item with the given key
 120          *
 121          * If the key includes a determistic input hash (e.g. the key can only have
 122          * the correct value) or complete staleness checks are handled by the caller
 123          * (e.g. nothing relies on the TTL), then the READ_VERIFIED flag should be set.
 124          * This lets tiered backends know they can safely upgrade a cached value to
 125          * higher tiers using standard TTLs.
 126          *
 127          * @param string $key
 128          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 129          * @param integer $oldFlags [unused]
 130          * @return mixed Returns false on failure and if the item does not exist
 131          */
 132         public function get( $key, $flags = 0, $oldFlags = null ) {
 133                 // B/C for ( $key, &$casToken = null, $flags = 0 )
 134                 $flags = is_int( $oldFlags ) ? $oldFlags : $flags;
 135
 136                 return $this->doGet( $key, $flags );
 137         }
 138
 139         /**
 140          * @param string $key
 141          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 142          * @return mixed Returns false on failure and if the item does not exist
 143          */
 144         abstract protected function doGet( $key, $flags = 0 );
 145
 146         /**
 147          * @note: This method is only needed if cas() is not is used for merge()
 148          *
 149          * @param string $key
 150          * @param mixed $casToken
 151          * @param integer $flags Bitfield of BagOStuff::READ_* constants [optional]
 152          * @return mixed Returns false on failure and if the item does not exist
 153          */
 154         protected function getWithToken( $key, &$casToken, $flags = 0 ) {
 155                 throw new Exception( __METHOD__ . ' not implemented.' );
 156         }
 157
 158         /**
 159          * Set an item
 160          *
 161          * @param string $key
 162          * @param mixed $value
 163          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 164          * @return bool Success
 165          */
 166         abstract public function set( $key, $value, $exptime = 0 );
 167
 168         /**
 169          * Delete an item
 170          *
 171          * @param string $key
 172          * @return bool True if the item was deleted or not found, false on failure
 173          */
 174         abstract public function delete( $key );
 175
 176         /**
 177          * Merge changes into the existing cache value (possibly creating a new one).
 178          * The callback function returns the new value given the current value
 179          * (which will be false if not present), and takes the arguments:
 180          * (this BagOStuff, cache key, current value).
 181          *
 182          * @param string $key
 183          * @param callable $callback Callback method to be executed
 184          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 185          * @param int $attempts The amount of times to attempt a merge in case of failure
 186          * @return bool Success
 187          * @throws InvalidArgumentException
 188          */
 189         public function merge( $key, $callback, $exptime = 0, $attempts = 10 ) {
 190                 if ( !is_callable( $callback ) ) {
 191                         throw new InvalidArgumentException( "Got invalid callback." );
 192                 }
 193
 194                 return $this->mergeViaLock( $key, $callback, $exptime, $attempts );
 195         }
 196
 197         /**
 198          * @see BagOStuff::merge()
 199          *
 200          * @param string $key
 201          * @param callable $callback Callback method to be executed
 202          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 203          * @param int $attempts The amount of times to attempt a merge in case of failure
 204          * @return bool Success
 205          */
 206         protected function mergeViaCas( $key, $callback, $exptime = 0, $attempts = 10 ) {
 207                 do {
 208                         $this->clearLastError();
 209                         $casToken = null; // passed by reference
 210                         $currentValue = $this->getWithToken( $key, $casToken, BagOStuff::READ_LATEST );
 211                         if ( $this->getLastError() ) {
 212                                 return false; // don't spam retries (retry only on races)
 213                         }
 214
 215                         // Derive the new value from the old value
 216                         $value = call_user_func( $callback, $this, $key, $currentValue );
 217
 218                         $this->clearLastError();
 219                         if ( $value === false ) {
 220                                 $success = true; // do nothing
 221                         } elseif ( $currentValue === false ) {
 222                                 // Try to create the key, failing if it gets created in the meantime
 223                                 $success = $this->add( $key, $value, $exptime );
 224                         } else {
 225                                 // Try to update the key, failing if it gets changed in the meantime
 226                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 227                         }
 228                         if ( $this->getLastError() ) {
 229                                 return false; // IO error; don't spam retries
 230                         }
 231                 } while ( !$success && --$attempts );
 232
 233                 return $success;
 234         }
 235
 236         /**
 237          * Check and set an item
 238          *
 239          * @param mixed $casToken
 240          * @param string $key
 241          * @param mixed $value
 242          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 243          * @return bool Success
 244          * @throws Exception
 245          */
 246         protected function cas( $casToken, $key, $value, $exptime = 0 ) {
 247                 throw new Exception( "CAS is not implemented in " . __CLASS__ );
 248         }
 249
 250         /**
 251          * @see BagOStuff::merge()
 252          *
 253          * @param string $key
 254          * @param callable $callback Callback method to be executed
 255          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 256          * @param int $attempts The amount of times to attempt a merge in case of failure
 257          * @return bool Success
 258          */
 259         protected function mergeViaLock( $key, $callback, $exptime = 0, $attempts = 10 ) {
 260                 if ( !$this->lock( $key, 6 ) ) {
 261                         return false;
 262                 }
 263
 264                 $this->clearLastError();
 265                 $currentValue = $this->get( $key, BagOStuff::READ_LATEST );
 266                 if ( $this->getLastError() ) {
 267                         $success = false;
 268                 } else {
 269                         // Derive the new value from the old value
 270                         $value = call_user_func( $callback, $this, $key, $currentValue );
 271                         if ( $value === false ) {
 272                                 $success = true; // do nothing
 273                         } else {
 274                                 $success = $this->set( $key, $value, $exptime ); // set the new value
 275                         }
 276                 }
 277
 278                 if ( !$this->unlock( $key ) ) {
 279                         // this should never happen
 280                         trigger_error( "Could not release lock for key '$key'." );
 281                 }
 282
 283                 return $success;
 284         }
 285
 286         /**
 287          * Acquire an advisory lock on a key string
 288          *
 289          * Note that if reentry is enabled, duplicate calls ignore $expiry
 290          *
 291          * @param string $key
 292          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 293          * @param int $expiry Lock expiry [optional]; 1 day maximum
 294          * @param string $rclass Allow reentry if set and the current lock used this value
 295          * @return bool Success
 296          */
 297         public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
 298                 // Avoid deadlocks and allow lock reentry if specified
 299                 if ( isset( $this->locks[$key] ) ) {
 300                         if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
 301                                 ++$this->locks[$key]['depth'];
 302                                 return true;
 303                         } else {
 304                                 return false;
 305                         }
 306                 }
 307
 308                 $expiry = min( $expiry ?: INF, 86400 );
 309
 310                 $this->clearLastError();
 311                 $timestamp = microtime( true ); // starting UNIX timestamp
 312                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 313                         $locked = true;
 314                 } elseif ( $this->getLastError() || $timeout <= 0 ) {
 315                         $locked = false; // network partition or non-blocking
 316                 } else {
 317                         $uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
 318                         $sleep = 2 * $uRTT; // rough time to do get()+set()
 319
 320                         $attempts = 0; // failed attempts
 321                         do {
 322                                 if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
 323                                         // Exponentially back off after failed attempts to avoid network spam.
 324                                         // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 325                                         $sleep *= 2;
 326                                 }
 327                                 usleep( $sleep ); // back off
 328                                 $this->clearLastError();
 329                                 $locked = $this->add( "{$key}:lock", 1, $expiry );
 330                                 if ( $this->getLastError() ) {
 331                                         $locked = false; // network partition
 332                                         break;
 333                                 }
 334                         } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 335                 }
 336
 337                 if ( $locked ) {
 338                         $this->locks[$key] = array( 'class' => $rclass, 'depth' => 1 );
 339                 }
 340
 341                 return $locked;
 342         }
 343
 344         /**
 345          * Release an advisory lock on a key string
 346          *
 347          * @param string $key
 348          * @return bool Success
 349          */
 350         public function unlock( $key ) {
 351                 if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
 352                         unset( $this->locks[$key] );
 353
 354                         return $this->delete( "{$key}:lock" );
 355                 }
 356
 357                 return true;
 358         }
 359
 360         /**
 361          * Get a lightweight exclusive self-unlocking lock
 362          *
 363          * Note that the same lock cannot be acquired twice.
 364          *
 365          * This is useful for task de-duplication or to avoid obtrusive
 366          * (though non-corrupting) DB errors like INSERT key conflicts
 367          * or deadlocks when using LOCK IN SHARE MODE.
 368          *
 369          * @param string $key
 370          * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
 371          * @param int $expiry Lock expiry [optional]; 1 day maximum
 372          * @param string $rclass Allow reentry if set and the current lock used this value
 373          * @return ScopedCallback|null Returns null on failure
 374          * @since 1.26
 375          */
 376         final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
 377                 $expiry = min( $expiry ?: INF, 86400 );
 378
 379                 if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
 380                         return null;
 381                 }
 382
 383                 $lSince = microtime( true ); // lock timestamp
 384                 // PHP 5.3: Can't use $this in a closure
 385                 $that = $this;
 386                 $logger = $this->logger;
 387
 388                 return new ScopedCallback( function() use ( $that, $logger, $key, $lSince, $expiry ) {
 389                         $latency = .050; // latency skew (err towards keeping lock present)
 390                         $age = ( microtime( true ) - $lSince + $latency );
 391                         if ( ( $age + $latency ) >= $expiry ) {
 392                                 $logger->warning( "Lock for $key held too long ($age sec)." );
 393                                 return; // expired; it's not "safe" to delete the key
 394                         }
 395                         $that->unlock( $key );
 396                 } );
 397         }
 398
 399         /**
 400          * Delete all objects expiring before a certain date.
 401          * @param string $date The reference date in MW format
 402          * @param callable|bool $progressCallback Optional, a function which will be called
 403          *     regularly during long-running operations with the percentage progress
 404          *     as the first parameter.
 405          *
 406          * @return bool Success, false if unimplemented
 407          */
 408         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 409                 // stub
 410                 return false;
 411         }
 412
 413         /**
 414          * Get an associative array containing the item for each of the keys that have items.
 415          * @param array $keys List of strings
 416          * @param integer $flags Bitfield; supports READ_LATEST [optional]
 417          * @return array
 418          */
 419         public function getMulti( array $keys, $flags = 0 ) {
 420                 $res = array();
 421                 foreach ( $keys as $key ) {
 422                         $val = $this->get( $key );
 423                         if ( $val !== false ) {
 424                                 $res[$key] = $val;
 425                         }
 426                 }
 427                 return $res;
 428         }
 429
 430         /**
 431          * Batch insertion
 432          * @param array $data $key => $value assoc array
 433          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 434          * @return bool Success
 435          * @since 1.24
 436          */
 437         public function setMulti( array $data, $exptime = 0 ) {
 438                 $res = true;
 439                 foreach ( $data as $key => $value ) {
 440                         if ( !$this->set( $key, $value, $exptime ) ) {
 441                                 $res = false;
 442                         }
 443                 }
 444                 return $res;
 445         }
 446
 447         /**
 448          * @param string $key
 449          * @param mixed $value
 450          * @param int $exptime
 451          * @return bool Success
 452          */
 453         public function add( $key, $value, $exptime = 0 ) {
 454                 if ( $this->get( $key ) === false ) {
 455                         return $this->set( $key, $value, $exptime );
 456                 }
 457                 return false; // key already set
 458         }
 459
 460         /**
 461          * Increase stored value of $key by $value while preserving its TTL
 462          * @param string $key Key to increase
 463          * @param int $value Value to add to $key (Default 1)
 464          * @return int|bool New value or false on failure
 465          */
 466         public function incr( $key, $value = 1 ) {
 467                 if ( !$this->lock( $key ) ) {
 468                         return false;
 469                 }
 470                 $n = $this->get( $key );
 471                 if ( $this->isInteger( $n ) ) { // key exists?
 472                         $n += intval( $value );
 473                         $this->set( $key, max( 0, $n ) ); // exptime?
 474                 } else {
 475                         $n = false;
 476                 }
 477                 $this->unlock( $key );
 478
 479                 return $n;
 480         }
 481
 482         /**
 483          * Decrease stored value of $key by $value while preserving its TTL
 484          * @param string $key
 485          * @param int $value
 486          * @return int|bool New value or false on failure
 487          */
 488         public function decr( $key, $value = 1 ) {
 489                 return $this->incr( $key, - $value );
 490         }
 491
 492         /**
 493          * Increase stored value of $key by $value while preserving its TTL
 494          *
 495          * This will create the key with value $init and TTL $ttl if not present
 496          *
 497          * @param string $key
 498          * @param int $ttl
 499          * @param int $value
 500          * @param int $init
 501          * @return bool
 502          * @since 1.24
 503          */
 504         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 505                 return $this->incr( $key, $value ) ||
 506                         $this->add( $key, (int)$init, $ttl ) || $this->incr( $key, $value );
 507         }
 508
 509         /**
 510          * Get the "last error" registered; clearLastError() should be called manually
 511          * @return int ERR_* constant for the "last error" registry
 512          * @since 1.23
 513          */
 514         public function getLastError() {
 515                 return $this->lastError;
 516         }
 517
 518         /**
 519          * Clear the "last error" registry
 520          * @since 1.23
 521          */
 522         public function clearLastError() {
 523                 $this->lastError = self::ERR_NONE;
 524         }
 525
 526         /**
 527          * Set the "last error" registry
 528          * @param int $err ERR_* constant
 529          * @since 1.23
 530          */
 531         protected function setLastError( $err ) {
 532                 $this->lastError = $err;
 533         }
 534
 535         /**
 536          * Modify a cache update operation array for EventRelayer::notify()
 537          *
 538          * This is used for relayed writes, e.g. for broadcasting a change
 539          * to multiple data-centers. If the array contains a 'val' field
 540          * then the command involves setting a key to that value. Note that
 541          * for simplicity, 'val' is always a simple scalar value. This method
 542          * is used to possibly serialize the value and add any cache-specific
 543          * key/values needed for the relayer daemon (e.g. memcached flags).
 544          *
 545          * @param array $event
 546          * @return array
 547          * @since 1.26
 548          */
 549         public function modifySimpleRelayEvent( array $event ) {
 550                 return $event;
 551         }
 552
 553         /**
 554          * @param string $text
 555          */
 556         protected function debug( $text ) {
 557                 if ( $this->debugMode ) {
 558                         $this->logger->debug( "{class} debug: $text", array(
 559                                 'class' => get_class( $this ),
 560                         ) );
 561                 }
 562         }
 563
 564         /**
 565          * Convert an optionally relative time to an absolute time
 566          * @param int $exptime
 567          * @return int
 568          */
 569         protected function convertExpiry( $exptime ) {
 570                 if ( ( $exptime != 0 ) && ( $exptime < 86400 * 3650 /* 10 years */ ) ) {
 571                         return time() + $exptime;
 572                 } else {
 573                         return $exptime;
 574                 }
 575         }
 576
 577         /**
 578          * Convert an optionally absolute expiry time to a relative time. If an
 579          * absolute time is specified which is in the past, use a short expiry time.
 580          *
 581          * @param int $exptime
 582          * @return int
 583          */
 584         protected function convertToRelative( $exptime ) {
 585                 if ( $exptime >= 86400 * 3650 /* 10 years */ ) {
 586                         $exptime -= time();
 587                         if ( $exptime <= 0 ) {
 588                                 $exptime = 1;
 589                         }
 590                         return $exptime;
 591                 } else {
 592                         return $exptime;
 593                 }
 594         }
 595
 596         /**
 597          * Check if a value is an integer
 598          *
 599          * @param mixed $value
 600          * @return bool
 601          */
 602         protected function isInteger( $value ) {
 603                 return ( is_int( $value ) || ctype_digit( $value ) );
 604         }
 605 }