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