includes/cache/CacheDependency.php

   1 <?php
   2 /**
   3  * Data caching with dependencies.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  * http://www.gnu.org/copyleft/gpl.html
  19  *
  20  * @file
  21  * @ingroup Cache
  22  */
  23
  24 /**
  25  * This class stores an arbitrary value along with its dependencies.
  26  * Users should typically only use DependencyWrapper::getValueFromCache(),
  27  * rather than instantiating one of these objects directly.
  28  * @ingroup Cache
  29  */
  30 class DependencyWrapper {
  31         private $value;
  32         /** @var CacheDependency[] */
  33         private $deps;
  34
  35         /**
  36          * Create an instance.
  37          * @param mixed $value The user-supplied value
  38          * @param CacheDependency|CacheDependency[] $deps A dependency or dependency
  39          *   array. All dependencies must be objects implementing CacheDependency.
  40          */
  41         function __construct( $value = false, $deps = array() ) {
  42                 $this->value = $value;
  43
  44                 if ( !is_array( $deps ) ) {
  45                         $deps = array( $deps );
  46                 }
  47
  48                 $this->deps = $deps;
  49         }
  50
  51         /**
  52          * Returns true if any of the dependencies have expired
  53          *
  54          * @return bool
  55          */
  56         function isExpired() {
  57                 foreach ( $this->deps as $dep ) {
  58                         if ( $dep->isExpired() ) {
  59                                 return true;
  60                         }
  61                 }
  62
  63                 return false;
  64         }
  65
  66         /**
  67          * Initialise dependency values in preparation for storing. This must be
  68          * called before serialization.
  69          */
  70         function initialiseDeps() {
  71                 foreach ( $this->deps as $dep ) {
  72                         $dep->loadDependencyValues();
  73                 }
  74         }
  75
  76         /**
  77          * Get the user-defined value
  78          * @return bool|mixed
  79          */
  80         function getValue() {
  81                 return $this->value;
  82         }
  83
  84         /**
  85          * Store the wrapper to a cache
  86          *
  87          * @param BagOStuff $cache
  88          * @param string $key
  89          * @param int $expiry
  90          */
  91         function storeToCache( $cache, $key, $expiry = 0 ) {
  92                 $this->initialiseDeps();
  93                 $cache->set( $key, $this, $expiry );
  94         }
  95
  96         /**
  97          * Attempt to get a value from the cache. If the value is expired or missing,
  98          * it will be generated with the callback function (if present), and the newly
  99          * calculated value will be stored to the cache in a wrapper.
 100          *
 101          * @param BagOStuff $cache A cache object such as $wgMemc
 102          * @param string $key The cache key
 103          * @param int $expiry The expiry timestamp or interval in seconds
 104          * @param bool|callable $callback The callback for generating the value, or false
 105          * @param array $callbackParams The function parameters for the callback
 106          * @param array $deps The dependencies to store on a cache miss. Note: these
 107          *    are not the dependencies used on a cache hit! Cache hits use the stored
 108          *    dependency array.
 109          *
 110          * @return mixed The value, or null if it was not present in the cache and no
 111          *    callback was defined.
 112          */
 113         static function getValueFromCache( $cache, $key, $expiry = 0, $callback = false,
 114                 $callbackParams = array(), $deps = array()
 115         ) {
 116                 $obj = $cache->get( $key );
 117
 118                 if ( is_object( $obj ) && $obj instanceof DependencyWrapper && !$obj->isExpired() ) {
 119                         $value = $obj->value;
 120                 } elseif ( $callback ) {
 121                         $value = call_user_func_array( $callback, $callbackParams );
 122                         # Cache the newly-generated value
 123                         $wrapper = new DependencyWrapper( $value, $deps );
 124                         $wrapper->storeToCache( $cache, $key, $expiry );
 125                 } else {
 126                         $value = null;
 127                 }
 128
 129                 return $value;
 130         }
 131 }
 132
 133 /**
 134  * @ingroup Cache
 135  */
 136 abstract class CacheDependency {
 137         /**
 138          * Returns true if the dependency is expired, false otherwise
 139          */
 140         abstract function isExpired();
 141
 142         /**
 143          * Hook to perform any expensive pre-serialize loading of dependency values.
 144          */
 145         function loadDependencyValues() {
 146         }
 147 }
 148
 149 /**
 150  * @ingroup Cache
 151  */
 152 class FileDependency extends CacheDependency {
 153         private $filename;
 154         private $timestamp;
 155
 156         /**
 157          * Create a file dependency
 158          *
 159          * @param string $filename The name of the file, preferably fully qualified
 160          * @param null|bool|int $timestamp The unix last modified timestamp, or false if the
 161          *        file does not exist. If omitted, the timestamp will be loaded from
 162          *        the file.
 163          *
 164          * A dependency on a nonexistent file will be triggered when the file is
 165          * created. A dependency on an existing file will be triggered when the
 166          * file is changed.
 167          */
 168         function __construct( $filename, $timestamp = null ) {
 169                 $this->filename = $filename;
 170                 $this->timestamp = $timestamp;
 171         }
 172
 173         /**
 174          * @return array
 175          */
 176         function __sleep() {
 177                 $this->loadDependencyValues();
 178
 179                 return array( 'filename', 'timestamp' );
 180         }
 181
 182         function loadDependencyValues() {
 183                 if ( is_null( $this->timestamp ) ) {
 184                         if ( !file_exists( $this->filename ) ) {
 185                                 # Dependency on a non-existent file
 186                                 # This is a valid concept!
 187                                 $this->timestamp = false;
 188                         } else {
 189                                 $this->timestamp = filemtime( $this->filename );
 190                         }
 191                 }
 192         }
 193
 194         /**
 195          * @return bool
 196          */
 197         function isExpired() {
 198                 if ( !file_exists( $this->filename ) ) {
 199                         if ( $this->timestamp === false ) {
 200                                 # Still nonexistent
 201                                 return false;
 202                         } else {
 203                                 # Deleted
 204                                 wfDebug( "Dependency triggered: {$this->filename} deleted.\n" );
 205
 206                                 return true;
 207                         }
 208                 } else {
 209                         $lastmod = filemtime( $this->filename );
 210                         if ( $lastmod > $this->timestamp ) {
 211                                 # Modified or created
 212                                 wfDebug( "Dependency triggered: {$this->filename} changed.\n" );
 213
 214                                 return true;
 215                         } else {
 216                                 # Not modified
 217                                 return false;
 218                         }
 219                 }
 220         }
 221 }
 222
 223 /**
 224  * @ingroup Cache
 225  */
 226 class GlobalDependency extends CacheDependency {
 227         private $name;
 228         private $value;
 229
 230         function __construct( $name ) {
 231                 $this->name = $name;
 232                 $this->value = $GLOBALS[$name];
 233         }
 234
 235         /**
 236          * @return bool
 237          */
 238         function isExpired() {
 239                 if ( !isset( $GLOBALS[$this->name] ) ) {
 240                         return true;
 241                 }
 242
 243                 return $GLOBALS[$this->name] != $this->value;
 244         }
 245 }
 246
 247 /**
 248  * @ingroup Cache
 249  */
 250 class ConstantDependency extends CacheDependency {
 251         private $name;
 252         private $value;
 253
 254         function __construct( $name ) {
 255                 $this->name = $name;
 256                 $this->value = constant( $name );
 257         }
 258
 259         /**
 260          * @return bool
 261          */
 262         function isExpired() {
 263                 return constant( $this->name ) != $this->value;
 264         }
 265 }