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         /**
  62          * Get an item with the given key. Returns false if it does not exist.
  63          * @param string $key
  64          * @param mixed $casToken [optional]
  65          * @return mixed Returns false on failure
  66          */
  67         abstract public function get( $key, &$casToken = null );
  68
  69         /**
  70          * Set an item.
  71          * @param string $key
  72          * @param mixed $value
  73          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  74          * @return bool Success
  75          */
  76         abstract public function set( $key, $value, $exptime = 0 );
  77
  78         /**
  79          * Check and set an item.
  80          * @param mixed $casToken
  81          * @param string $key
  82          * @param mixed $value
  83          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
  84          * @return bool Success
  85          */
  86         abstract public function cas( $casToken, $key, $value, $exptime = 0 );
  87
  88         /**
  89          * Delete an item.
  90          * @param string $key
  91          * @return bool True if the item was deleted or not found, false on failure
  92          */
  93         abstract public function delete( $key );
  94
  95         /**
  96          * Merge changes into the existing cache value (possibly creating a new one).
  97          * The callback function returns the new value given the current value (possibly false),
  98          * and takes the arguments: (this BagOStuff object, cache key, current value).
  99          *
 100          * @param string $key
 101          * @param Closure $callback Callback method to be executed
 102          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 103          * @param int $attempts The amount of times to attempt a merge in case of failure
 104          * @return bool Success
 105          */
 106         public function merge( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 107                 return $this->mergeViaCas( $key, $callback, $exptime, $attempts );
 108         }
 109
 110         /**
 111          * @see BagOStuff::merge()
 112          *
 113          * @param string $key
 114          * @param Closure $callback Callback method to be executed
 115          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 116          * @param int $attempts The amount of times to attempt a merge in case of failure
 117          * @return bool Success
 118          */
 119         protected function mergeViaCas( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 120                 do {
 121                         $casToken = null; // passed by reference
 122                         $currentValue = $this->get( $key, $casToken ); // get the old value
 123                         $value = $callback( $this, $key, $currentValue ); // derive the new value
 124
 125                         if ( $value === false ) {
 126                                 $success = true; // do nothing
 127                         } elseif ( $currentValue === false ) {
 128                                 // Try to create the key, failing if it gets created in the meantime
 129                                 $success = $this->add( $key, $value, $exptime );
 130                         } else {
 131                                 // Try to update the key, failing if it gets changed in the meantime
 132                                 $success = $this->cas( $casToken, $key, $value, $exptime );
 133                         }
 134                 } while ( !$success && --$attempts );
 135
 136                 return $success;
 137         }
 138
 139         /**
 140          * @see BagOStuff::merge()
 141          *
 142          * @param string $key
 143          * @param Closure $callback Callback method to be executed
 144          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 145          * @param int $attempts The amount of times to attempt a merge in case of failure
 146          * @return bool Success
 147          */
 148         protected function mergeViaLock( $key, Closure $callback, $exptime = 0, $attempts = 10 ) {
 149                 if ( !$this->lock( $key, 6 ) ) {
 150                         return false;
 151                 }
 152
 153                 $currentValue = $this->get( $key ); // get the old value
 154                 $value = $callback( $this, $key, $currentValue ); // derive the new value
 155
 156                 if ( $value === false ) {
 157                         $success = true; // do nothing
 158                 } else {
 159                         $success = $this->set( $key, $value, $exptime ); // set the new value
 160                 }
 161
 162                 if ( !$this->unlock( $key ) ) {
 163                         // this should never happen
 164                         trigger_error( "Could not release lock for key '$key'." );
 165                 }
 166
 167                 return $success;
 168         }
 169
 170         /**
 171          * @param string $key
 172          * @param int $timeout Lock wait timeout [optional]
 173          * @param int $expiry Lock expiry [optional]
 174          * @return bool Success
 175          */
 176         public function lock( $key, $timeout = 6, $expiry = 6 ) {
 177                 $this->clearLastError();
 178                 $timestamp = microtime( true ); // starting UNIX timestamp
 179                 if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
 180                         return true;
 181                 } elseif ( $this->getLastError() ) {
 182                         return false;
 183                 }
 184
 185                 $uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
 186                 $sleep = 2 * $uRTT; // rough time to do get()+set()
 187
 188                 $locked = false; // lock acquired
 189                 $attempts = 0; // failed attempts
 190                 do {
 191                         if ( ++$attempts >= 3 && $sleep <= 1e6 ) {
 192                                 // Exponentially back off after failed attempts to avoid network spam.
 193                                 // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
 194                                 $sleep *= 2;
 195                         }
 196                         usleep( $sleep ); // back off
 197                         $this->clearLastError();
 198                         $locked = $this->add( "{$key}:lock", 1, $expiry );
 199                         if ( $this->getLastError() ) {
 200                                 return false;
 201                         }
 202                 } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
 203
 204                 return $locked;
 205         }
 206
 207         /**
 208          * @param string $key
 209          * @return bool Success
 210          */
 211         public function unlock( $key ) {
 212                 return $this->delete( "{$key}:lock" );
 213         }
 214
 215         /**
 216          * Delete all objects expiring before a certain date.
 217          * @param string $date The reference date in MW format
 218          * @param callable|bool $progressCallback Optional, a function which will be called
 219          *     regularly during long-running operations with the percentage progress
 220          *     as the first parameter.
 221          *
 222          * @return bool Success, false if unimplemented
 223          */
 224         public function deleteObjectsExpiringBefore( $date, $progressCallback = false ) {
 225                 // stub
 226                 return false;
 227         }
 228
 229         /* *** Emulated functions *** */
 230
 231         /**
 232          * Get an associative array containing the item for each of the keys that have items.
 233          * @param array $keys List of strings
 234          * @return array
 235          */
 236         public function getMulti( array $keys ) {
 237                 $res = array();
 238                 foreach ( $keys as $key ) {
 239                         $val = $this->get( $key );
 240                         if ( $val !== false ) {
 241                                 $res[$key] = $val;
 242                         }
 243                 }
 244                 return $res;
 245         }
 246
 247         /**
 248          * Batch insertion
 249          * @param array $data $key => $value assoc array
 250          * @param int $exptime Either an interval in seconds or a unix timestamp for expiry
 251          * @return bool Success
 252          * @since 1.24
 253          */
 254         public function setMulti( array $data, $exptime = 0 ) {
 255                 $res = true;
 256                 foreach ( $data as $key => $value ) {
 257                         if ( !$this->set( $key, $value, $exptime ) ) {
 258                                 $res = false;
 259                         }
 260                 }
 261                 return $res;
 262         }
 263
 264         /**
 265          * @param string $key
 266          * @param mixed $value
 267          * @param int $exptime
 268          * @return bool Success
 269          */
 270         public function add( $key, $value, $exptime = 0 ) {
 271                 if ( $this->get( $key ) === false ) {
 272                         return $this->set( $key, $value, $exptime );
 273                 }
 274                 return false; // key already set
 275         }
 276
 277         /**
 278          * Increase stored value of $key by $value while preserving its TTL
 279          * @param string $key Key to increase
 280          * @param int $value Value to add to $key (Default 1)
 281          * @return int|bool New value or false on failure
 282          */
 283         public function incr( $key, $value = 1 ) {
 284                 if ( !$this->lock( $key ) ) {
 285                         return false;
 286                 }
 287                 $n = $this->get( $key );
 288                 if ( $this->isInteger( $n ) ) { // key exists?
 289                         $n += intval( $value );
 290                         $this->set( $key, max( 0, $n ) ); // exptime?
 291                 } else {
 292                         $n = false;
 293                 }
 294                 $this->unlock( $key );
 295
 296                 return $n;
 297         }
 298
 299         /**
 300          * Decrease stored value of $key by $value while preserving its TTL
 301          * @param string $key
 302          * @param int $value
 303          * @return int
 304          */
 305         public function decr( $key, $value = 1 ) {
 306                 return $this->incr( $key, - $value );
 307         }
 308
 309         /**
 310          * Increase stored value of $key by $value while preserving its TTL
 311          *
 312          * This will create the key with value $init and TTL $ttl if not present
 313          *
 314          * @param string $key
 315          * @param int $ttl
 316          * @param int $value
 317          * @param int $init
 318          * @return bool
 319          * @since 1.24
 320          */
 321         public function incrWithInit( $key, $ttl, $value = 1, $init = 1 ) {
 322                 return $this->incr( $key, $value ) ||
 323                         $this->add( $key, (int)$init, $ttl ) || $this->incr( $key, $value );
 324         }
 325
 326         /**
 327          * Get the "last error" registered; clearLastError() should be called manually
 328          * @return int ERR_* constant for the "last error" registry
 329          * @since 1.23
 330          */
 331         public function getLastError() {
 332                 return $this->lastError;
 333         }
 334
 335         /**
 336          * Clear the "last error" registry
 337          * @since 1.23
 338          */
 339         public function clearLastError() {
 340                 $this->lastError = self::ERR_NONE;
 341         }
 342
 343         /**
 344          * Set the "last error" registry
 345          * @param int $err ERR_* constant
 346          * @since 1.23
 347          */
 348         protected function setLastError( $err ) {
 349                 $this->lastError = $err;
 350         }
 351
 352         /**
 353          * @param string $text
 354          */
 355         public function debug( $text ) {
 356                 if ( $this->debugMode ) {
 357                         $class = get_class( $this );
 358                         wfDebug( "$class debug: $text\n" );
 359                 }
 360         }
 361
 362         /**
 363          * Convert an optionally relative time to an absolute time
 364          * @param int $exptime
 365          * @return int
 366          */
 367         protected function convertExpiry( $exptime ) {
 368                 if ( ( $exptime != 0 ) && ( $exptime < 86400 * 3650 /* 10 years */ ) ) {
 369                         return time() + $exptime;
 370                 } else {
 371                         return $exptime;
 372                 }
 373         }
 374
 375         /**
 376          * Convert an optionally absolute expiry time to a relative time. If an
 377          * absolute time is specified which is in the past, use a short expiry time.
 378          *
 379          * @param int $exptime
 380          * @return int
 381          */
 382         protected function convertToRelative( $exptime ) {
 383                 if ( $exptime >= 86400 * 3650 /* 10 years */ ) {
 384                         $exptime -= time();
 385                         if ( $exptime <= 0 ) {
 386                                 $exptime = 1;
 387                         }
 388                         return $exptime;
 389                 } else {
 390                         return $exptime;
 391                 }
 392         }
 393
 394         /**
 395          * Check if a value is an integer
 396          *
 397          * @param mixed $value
 398          * @return bool
 399          */
 400         protected function isInteger( $value ) {
 401                 return ( is_int( $value ) || ctype_digit( $value ) );
 402         }
 403 }