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