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