includes/objectcache/BagOStuff.php

   1 <?php
   2 /**
   3  * Classes to cache objects in PHP accelerators, SQL database or DBA files
   4  *
   5  * Copyright © 2003-2004 Brion Vibber <brion@pobox.com>
   6  * https://www.mediawiki.org/
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License along
  19  * with this program; if not, write to the Free Software Foundation, Inc.,
  20  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  21  * http://www.gnu.org/copyleft/gpl.html
  22  *
  23  * @file
  24  * @ingroup Cache
  25  */
  26
  27 /**
  28  * @defgroup Cache Cache
  29  */
  30
  31 /**
  32  * interface is intended to be more or less compatible with
  33  * the PHP memcached client.
  34  *
  35  * backends for local hash array and SQL table included:
  36  * <code>
  37  *   $bag = new HashBagOStuff();
  38  *   $bag = new SqlBagOStuff(); # connect to db first
  39  * </code>
  40  *
  41  * @ingroup Cache
  42  */
  43 abstract class BagOStuff {
  44         private $debugMode = false;
  45
  46         protected $lastError = self::ERR_NONE;
  47
  48         /** Possible values for getLastError() */
  49         const ERR_NONE = 0; // no error
  50         const ERR_NO_RESPONSE = 1; // no response
  51         const ERR_UNREACHABLE = 2; // can't connect
  52         const ERR_UNEXPECTED = 3; // response gave some error
  53
  54         /**
  55          * @param bool $bool
  56          */
  57         public function setDebug( $bool ) {
  58                 $this->debugMode = $bool;
  59         }
  60
  61         /* *** THE GUTS OF THE OPERATION *** */
  62         /* Override these with functional things in subclasses */
  63
  64         /**
  65          * Get an item with the given key. Returns false if it does not exist.
  66          * @param string $key
  67          * @param mixed $casToken [optional]
  68          * @return mixed Returns false on failure
  69          */
  70         abstract public function get( $key, &$casToken = null );
  71
  72         /**
  73          * Set an item.
  74          * @param string $key
  75          * @param mixed $value
  76          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  77          * @return bool Success
  78          */
  79         abstract public function set( $key, $value, $exptime = 0 );
  80
  81         /**
  82          * Check and set an item.
  83          * @param mixed $casToken
  84          * @param string $key
  85          * @param mixed $value
  86          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  87          * @return bool Success
  88          */
  89         abstract public function cas( $casToken, $key, $value, $exptime = 0 );
  90
  91         /**
  92          * Delete an item.
  93          * @param string $key
  94          * @param int $time Amount of time to delay the operation (mostly memcached-specific)
  95          * @return bool True if the item was deleted or not found, false on failure
  96          */
  97         abstract public function delete( $key, $time = 0 );
  98
  99         /**
 100          * Merge changes into the existing cache value (possibly creating a new one).
 101          * The callback function returns the new value given the current value (possibly false),
 102          * and takes the arguments: (this BagOStuff object, cache key, current value).
 103          *
 104          * @param string $key
 105          * @param Closure $callback Callback method to be executed
 106          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 107          * @param int $attempts The amount of times to attempt a merge in case of failure
 108          * @return bool Success
 109          */
 110         public function merge( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 111                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 112         }
 113
 114         /**
 115          * @see BagOStuff::merge()
 116          *
 117          * @param string $key
 118          * @param Closure $callback Callback method to be executed
 119          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 120          * @param int $attempts The amount of times to attempt a merge in case of failure
 121          * @return bool Success
 122          */
 123         protected function mergeViaCas( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 124                 do {
 125                         $casToken = null; // passed by reference
 126                         $currentValue = $this->get( $key, $casToken ); // get the old value
 127                         $value = $callback( $this, $key, $currentValue ); // derive the new value
 128
 129                         if ( $value === false ) {
 130                                 $success = true; // do nothing
 131                         } elseif ( $currentValue === false ) {
 132                                 // Try to create the key, failing if it gets created in the meantime
 133                                 $success = $this->add( $key, $value, $exptime );
 134                         } else {
 135                                 // Try to update the key, failing if it gets changed in the meantime
 136                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 137                         }
 138                 } while ( !$success && --$attempts );
 139
 140                 return $success;
 141         }
 142
 143         /**
 144          * @see BagOStuff::merge()
 145          *
 146          * @param string $key
 147          * @param Closure $callback Callback method to be executed
 148          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 149          * @param int $attempts The amount of times to attempt a merge in case of failure
 150          * @return bool Success
 151          */
 152         protected function mergeViaLock( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 153                 if ( !$this->lock( $key, 6 ) ) {
 154                         return false;
 155                 }
 156
 157                 $currentValue = $this->get( $key ); // get the old value
 158                 $value = $callback( $this, $key, $currentValue ); // derive the new value
 159
 160                 if ( $value === false ) {
 161                         $success = true; // do nothing
 162                 } else {
 163                         $success = $this->set( $key, $value, $exptime ); // set the new value
 164                 }
 165
 166                 if ( !$this->unlock( $key ) ) {
 167                         // this should never happen
 168                         trigger_error( "Could not release lock for key '$key'." );
 169                 }
 170
 171                 return $success;
 172         }
 173
 174         /**
 175          * @param string $key
 176          * @param int $timeout Lock wait timeout [optional]
 177          * @param int $expiry Lock expiry [optional]
 178          * @return bool Success
 179          */
 180         public function lock( $key, $timeout = 6, $expiry = 6 ) {
 181                 $this->clearLastError();
 182                 $timestamp = microtime( true ); // starting UNIX timestamp
 183                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 184                         return true;
 185                 } elseif ( $this->getLastError() ) {
 186                         return false;
 187                 }
 188
 189                 $uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
 190                 $sleep = 2 * $uRTT; // rough time to do get()+set()
 191
 192                 $locked = false; // lock acquired
 193                 $attempts = 0; // failed attempts
 194                 do {
 195                         if ( ++$attempts >= 3 && $sleep <= 1e6 ) {
 196                                 // Exponentially back off after failed attempts to avoid network spam.
 197                                 // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 198                                 $sleep *= 2;
 199                         }
 200                         usleep( $sleep ); // back off
 201                         $this->clearLastError();
 202                         $locked = $this->add( "{$key}:lock", 1, $expiry );
 203                         if ( $this->getLastError() ) {
 204                                 return false;
 205                         }
 206                 } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 207
 208                 return $locked;
 209         }
 210
 211         /**
 212          * @param string $key
 213          * @return bool Success
 214          */
 215         public function unlock( $key ) {
 216                 return $this->delete( "{$key}:lock" );
 217         }
 218
 219         /**
 220          * Delete all objects expiring before a certain date.
 221          * @param string $date The reference date in MW format
 222          * @param callable|bool $progressCallback Optional, a function which will be called
 223          *     regularly during long-running operations with the percentage progress
 224          *     as the first parameter.
 225          *
 226          * @return bool Success, false if unimplemented
 227          */
 228         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 229                 // stub
 230                 return false;
 231         }
 232
 233         /* *** Emulated functions *** */
 234
 235         /**
 236          * Get an associative array containing the item for each of the keys that have items.
 237          * @param array $keys List of strings
 238          * @return array
 239          */
 240         public function getMulti( array $keys ) {
 241                 $res = array();
 242                 foreach ( $keys as $key ) {
 243                         $val = $this->get( $key );
 244                         if ( $val !== false ) {
 245                                 $res[$key] = $val;
 246                         }
 247                 }
 248                 return $res;
 249         }
 250
 251         /**
 252          * Batch insertion
 253          * @param array $data $key => $value assoc array
 254          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 255          * @return bool Success
 256          * @since 1.24
 257          */
 258         public function setMulti( array $data, $exptime = 0 ) {
 259                 $res = true;
 260                 foreach ( $data as $key => $value ) {
 261                         if ( !$this->set( $key, $value, $exptime ) ) {
 262                                 $res = false;
 263                         }
 264                 }
 265                 return $res;
 266         }
 267
 268         /**
 269          * @param string $key
 270          * @param mixed $value
 271          * @param int $exptime
 272          * @return bool Success
 273          */
 274         public function add( $key, $value, $exptime = 0 ) {
 275                 if ( $this->get( $key ) === false ) {
 276                         return $this->set( $key, $value, $exptime );
 277                 }
 278                 return false; // key already set
 279         }
 280
 281         /**
 282          * Increase stored value of $key by $value while preserving its TTL
 283          * @param string $key Key to increase
 284          * @param int $value Value to add to $key (Default 1)
 285          * @return int|bool New value or false on failure
 286          */
 287         public function incr( $key, $value = 1 ) {
 288                 if ( !$this->lock( $key ) ) {
 289                         return false;
 290                 }
 291                 $n = $this->get( $key );
 292                 if ( $this->isInteger( $n ) ) { // key exists?
 293                         $n += intval( $value );
 294                         $this->set( $key, max( 0, $n ) ); // exptime?
 295                 } else {
 296                         $n = false;
 297                 }
 298                 $this->unlock( $key );
 299
 300                 return $n;
 301         }
 302
 303         /**
 304          * Decrease stored value of $key by $value while preserving its TTL
 305          * @param string $key
 306          * @param int $value
 307          * @return int
 308          */
 309         public function decr( $key, $value = 1 ) {
 310                 return $this->incr( $key, - $value );
 311         }
 312
 313         /**
 314          * Increase stored value of $key by $value while preserving its TTL
 315          *
 316          * This will create the key with value $init and TTL $ttl if not present
 317          *
 318          * @param string $key
 319          * @param int $ttl
 320          * @param int $value
 321          * @param int $init
 322          * @return bool
 323          * @since 1.24
 324          */
 325         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 326                 return $this->incr( $key, $value ) ||
 327                         $this->add( $key, (int)$init, $ttl ) || $this->incr( $key, $value );
 328         }
 329
 330         /**
 331          * Get the "last error" registered; clearLastError() should be called manually
 332          * @return int ERR_* constant for the "last error" registry
 333          * @since 1.23
 334          */
 335         public function getLastError() {
 336                 return $this->lastError;
 337         }
 338
 339         /**
 340          * Clear the "last error" registry
 341          * @since 1.23
 342          */
 343         public function clearLastError() {
 344                 $this->lastError = self::ERR_NONE;
 345         }
 346
 347         /**
 348          * Set the "last error" registry
 349          * @param int $err ERR_* constant
 350          * @since 1.23
 351          */
 352         protected function setLastError( $err ) {
 353                 $this->lastError = $err;
 354         }
 355
 356         /**
 357          * @param string $text
 358          */
 359         public function debug( $text ) {
 360                 if ( $this->debugMode ) {
 361                         $class = get_class( $this );
 362                         wfDebug( "$class debug: $text\n" );
 363                 }
 364         }
 365
 366         /**
 367          * Convert an optionally relative time to an absolute time
 368          * @param int $exptime
 369          * @return int
 370          */
 371         protected function convertExpiry( $exptime ) {
 372                 if ( ( $exptime != 0 ) && ( $exptime < 86400 * 3650 /* 10 years */ ) ) {
 373                         return time() + $exptime;
 374                 } else {
 375                         return $exptime;
 376                 }
 377         }
 378
 379         /**
 380          * Convert an optionally absolute expiry time to a relative time. If an
 381          * absolute time is specified which is in the past, use a short expiry time.
 382          *
 383          * @param int $exptime
 384          * @return int
 385          */
 386         protected function convertToRelative( $exptime ) {
 387                 if ( $exptime >= 86400 * 3650 /* 10 years */ ) {
 388                         $exptime -= time();
 389                         if ( $exptime <= 0 ) {
 390                                 $exptime = 1;
 391                         }
 392                         return $exptime;
 393                 } else {
 394                         return $exptime;
 395                 }
 396         }
 397
 398         /**
 399          * Check if a value is an integer
 400          *
 401          * @param mixed $value
 402          * @return bool
 403          */
 404         protected function isInteger( $value ) {
 405                 return ( is_int( $value ) || ctype_digit( $value ) );
 406         }
 407 }