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