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/wp-includes/ -> cache.php (source)

   1  <?php
   2  /**
   3   * Object Cache API
   4   *
   5   * @link https://codex.wordpress.org/Class_Reference/WP_Object_Cache
   6   *
   7   * @package WordPress
   8   * @subpackage Cache
   9   */
  10  
  11  /**
  12   * Adds data to the cache, if the cache key doesn't already exist.
  13   *
  14   * @since 2.0.0
  15   *
  16   * @see WP_Object_Cache::add()
  17   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
  18   *
  19   * @param int|string $key    The cache key to use for retrieval later.
  20   * @param mixed      $data   The data to add to the cache.
  21   * @param string     $group  Optional. The group to add the cache to. Enables the same key
  22   *                           to be used across groups. Default empty.
  23   * @param int        $expire Optional. When the cache data should expire, in seconds.
  24   *                           Default 0 (no expiration).
  25   * @return bool False if cache key and group already exist, true on success.
  26   */
  27  function wp_cache_add( $key, $data, $group = '', $expire = 0 ) {
  28      global $wp_object_cache;
  29  
  30      return $wp_object_cache->add( $key, $data, $group, (int) $expire );
  31  }
  32  
  33  /**
  34   * Closes the cache.
  35   *
  36   * This function has ceased to do anything since WordPress 2.5. The
  37   * functionality was removed along with the rest of the persistent cache.
  38   *
  39   * This does not mean that plugins can't implement this function when they need
  40   * to make sure that the cache is cleaned up after WordPress no longer needs it.
  41   *
  42   * @since 2.0.0
  43   *
  44   * @return true Always returns true.
  45   */
  46  function wp_cache_close() {
  47      return true;
  48  }
  49  
  50  /**
  51   * Decrements numeric cache item's value.
  52   *
  53   * @since 3.3.0
  54   *
  55   * @see WP_Object_Cache::decr()
  56   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
  57   *
  58   * @param int|string $key    The cache key to decrement.
  59   * @param int        $offset Optional. The amount by which to decrement the item's value. Default 1.
  60   * @param string     $group  Optional. The group the key is in. Default empty.
  61   * @return false|int False on failure, the item's new value on success.
  62   */
  63  function wp_cache_decr( $key, $offset = 1, $group = '' ) {
  64      global $wp_object_cache;
  65  
  66      return $wp_object_cache->decr( $key, $offset, $group );
  67  }
  68  
  69  /**
  70   * Removes the cache contents matching key and group.
  71   *
  72   * @since 2.0.0
  73   *
  74   * @see WP_Object_Cache::delete()
  75   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
  76   *
  77   * @param int|string $key   What the contents in the cache are called.
  78   * @param string     $group Optional. Where the cache contents are grouped. Default empty.
  79   * @return bool True on successful removal, false on failure.
  80   */
  81  function wp_cache_delete( $key, $group = '' ) {
  82      global $wp_object_cache;
  83  
  84      return $wp_object_cache->delete( $key, $group );
  85  }
  86  
  87  /**
  88   * Removes all cache items.
  89   *
  90   * @since 2.0.0
  91   *
  92   * @see WP_Object_Cache::flush()
  93   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
  94   *
  95   * @return bool False on failure, true on success
  96   */
  97  function wp_cache_flush() {
  98      global $wp_object_cache;
  99  
 100      return $wp_object_cache->flush();
 101  }
 102  
 103  /**
 104   * Retrieves the cache contents from the cache by key and group.
 105   *
 106   * @since 2.0.0
 107   *
 108   * @see WP_Object_Cache::get()
 109   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
 110   *
 111   * @param int|string  $key    The key under which the cache contents are stored.
 112   * @param string      $group  Optional. Where the cache contents are grouped. Default empty.
 113   * @param bool        $force  Optional. Whether to force an update of the local cache from the persistent
 114   *                            cache. Default false.
 115   * @param bool        $found  Optional. Whether the key was found in the cache (passed by reference).
 116   *                            Disambiguates a return of false, a storable value. Default null.
 117   * @return bool|mixed False on failure to retrieve contents or the cache
 118   *                    contents on success
 119   */
 120  function wp_cache_get( $key, $group = '', $force = false, &$found = null ) {
 121      global $wp_object_cache;
 122  
 123      return $wp_object_cache->get( $key, $group, $force, $found );
 124  }
 125  
 126  /**
 127   * Increment numeric cache item's value
 128   *
 129   * @since 3.3.0
 130   *
 131   * @see WP_Object_Cache::incr()
 132   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
 133   *
 134   * @param int|string $key    The key for the cache contents that should be incremented.
 135   * @param int        $offset Optional. The amount by which to increment the item's value. Default 1.
 136   * @param string     $group  Optional. The group the key is in. Default empty.
 137   * @return false|int False on failure, the item's new value on success.
 138   */
 139  function wp_cache_incr( $key, $offset = 1, $group = '' ) {
 140      global $wp_object_cache;
 141  
 142      return $wp_object_cache->incr( $key, $offset, $group );
 143  }
 144  
 145  /**
 146   * Sets up Object Cache Global and assigns it.
 147   *
 148   * @since 2.0.0
 149   *
 150   * @global WP_Object_Cache $wp_object_cache
 151   */
 152  function wp_cache_init() {
 153      $GLOBALS['wp_object_cache'] = new WP_Object_Cache();
 154  }
 155  
 156  /**
 157   * Replaces the contents of the cache with new data.
 158   *
 159   * @since 2.0.0
 160   *
 161   * @see WP_Object_Cache::replace()
 162   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
 163   *
 164   * @param int|string $key    The key for the cache data that should be replaced.
 165   * @param mixed      $data   The new data to store in the cache.
 166   * @param string     $group  Optional. The group for the cache data that should be replaced.
 167   *                           Default empty.
 168   * @param int        $expire Optional. When to expire the cache contents, in seconds.
 169   *                           Default 0 (no expiration).
 170   * @return bool False if original value does not exist, true if contents were replaced
 171   */
 172  function wp_cache_replace( $key, $data, $group = '', $expire = 0 ) {
 173      global $wp_object_cache;
 174  
 175      return $wp_object_cache->replace( $key, $data, $group, (int) $expire );
 176  }
 177  
 178  /**
 179   * Saves the data to the cache.
 180   *
 181   * Differs from wp_cache_add() and wp_cache_replace() in that it will always write data.
 182   *
 183   * @since 2.0.0
 184   *
 185   * @see WP_Object_Cache::set()
 186   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
 187   *
 188   * @param int|string $key    The cache key to use for retrieval later.
 189   * @param mixed      $data   The contents to store in the cache.
 190   * @param string     $group  Optional. Where to group the cache contents. Enables the same key
 191   *                           to be used across groups. Default empty.
 192   * @param int        $expire Optional. When to expire the cache contents, in seconds.
 193   *                           Default 0 (no expiration).
 194   * @return bool False on failure, true on success
 195   */
 196  function wp_cache_set( $key, $data, $group = '', $expire = 0 ) {
 197      global $wp_object_cache;
 198  
 199      return $wp_object_cache->set( $key, $data, $group, (int) $expire );
 200  }
 201  
 202  /**
 203   * Switches the internal blog ID.
 204   *
 205   * This changes the blog id used to create keys in blog specific groups.
 206   *
 207   * @since 3.5.0
 208   *
 209   * @see WP_Object_Cache::switch_to_blog()
 210   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
 211   *
 212   * @param int $blog_id Site ID.
 213   */
 214  function wp_cache_switch_to_blog( $blog_id ) {
 215      global $wp_object_cache;
 216  
 217      $wp_object_cache->switch_to_blog( $blog_id );
 218  }
 219  
 220  /**
 221   * Adds a group or set of groups to the list of global groups.
 222   *
 223   * @since 2.6.0
 224   *
 225   * @see WP_Object_Cache::add_global_groups()
 226   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
 227   *
 228   * @param string|array $groups A group or an array of groups to add.
 229   */
 230  function wp_cache_add_global_groups( $groups ) {
 231      global $wp_object_cache;
 232  
 233      $wp_object_cache->add_global_groups( $groups );
 234  }
 235  
 236  /**
 237   * Adds a group or set of groups to the list of non-persistent groups.
 238   *
 239   * @since 2.6.0
 240   *
 241   * @param string|array $groups A group or an array of groups to add.
 242   */
 243  function wp_cache_add_non_persistent_groups( $groups ) {
 244      // Default cache doesn't persist so nothing to do here.
 245  }
 246  
 247  /**
 248   * Reset internal cache keys and structures.
 249   *
 250   * If the cache back end uses global blog or site IDs as part of its cache keys,
 251   * this function instructs the back end to reset those keys and perform any cleanup
 252   * since blog or site IDs have changed since cache init.
 253   *
 254   * This function is deprecated. Use wp_cache_switch_to_blog() instead of this
 255   * function when preparing the cache for a blog switch. For clearing the cache
 256   * during unit tests, consider using wp_cache_init(). wp_cache_init() is not
 257   * recommended outside of unit tests as the performance penalty for using it is
 258   * high.
 259   *
 260   * @since 2.6.0
 261   * @deprecated 3.5.0 WP_Object_Cache::reset()
 262   * @see WP_Object_Cache::reset()
 263   *
 264   * @global WP_Object_Cache $wp_object_cache Object cache global instance.
 265   */
 266  function wp_cache_reset() {
 267      _deprecated_function( __FUNCTION__, '3.5.0', 'WP_Object_Cache::reset()' );
 268  
 269      global $wp_object_cache;
 270  
 271      $wp_object_cache->reset();
 272  }
 273  
 274  /**
 275   * Core class that implements an object cache.
 276   *
 277   * The WordPress Object Cache is used to save on trips to the database. The
 278   * Object Cache stores all of the cache data to memory and makes the cache
 279   * contents available by using a key, which is used to name and later retrieve
 280   * the cache contents.
 281   *
 282   * The Object Cache can be replaced by other caching mechanisms by placing files
 283   * in the wp-content folder which is looked at in wp-settings. If that file
 284   * exists, then this file will not be included.
 285   *
 286   * @since 2.0.0
 287   */
 288  class WP_Object_Cache {
 289  
 290      /**
 291       * Holds the cached objects.
 292       *
 293       * @since 2.0.0
 294       * @var array
 295       */
 296      private $cache = array();
 297  
 298      /**
 299       * The amount of times the cache data was already stored in the cache.
 300       *
 301       * @since 2.5.0
 302       * @var int
 303       */
 304      public $cache_hits = 0;
 305  
 306      /**
 307       * Amount of times the cache did not have the request in cache.
 308       *
 309       * @since 2.0.0
 310       * @var int
 311       */
 312      public $cache_misses = 0;
 313  
 314      /**
 315       * List of global cache groups.
 316       *
 317       * @since 3.0.0
 318       * @var array
 319       */
 320      protected $global_groups = array();
 321  
 322      /**
 323       * The blog prefix to prepend to keys in non-global groups.
 324       *
 325       * @since 3.5.0
 326       * @var string
 327       */
 328      private $blog_prefix;
 329  
 330      /**
 331       * Holds the value of is_multisite().
 332       *
 333       * @since 3.5.0
 334       * @var bool
 335       */
 336      private $multisite;
 337  
 338      /**
 339       * Makes private properties readable for backward compatibility.
 340       *
 341       * @since 4.0.0
 342       *
 343       * @param string $name Property to get.
 344       * @return mixed Property.
 345       */
 346  	public function __get( $name ) {
 347          return $this->$name;
 348      }
 349  
 350      /**
 351       * Makes private properties settable for backward compatibility.
 352       *
 353       * @since 4.0.0
 354       *
 355       * @param string $name  Property to set.
 356       * @param mixed  $value Property value.
 357       * @return mixed Newly-set property.
 358       */
 359  	public function __set( $name, $value ) {
 360          return $this->$name = $value;
 361      }
 362  
 363      /**
 364       * Makes private properties checkable for backward compatibility.
 365       *
 366       * @since 4.0.0
 367       *
 368       * @param string $name Property to check if set.
 369       * @return bool Whether the property is set.
 370       */
 371  	public function __isset( $name ) {
 372          return isset( $this->$name );
 373      }
 374  
 375      /**
 376       * Makes private properties un-settable for backward compatibility.
 377       *
 378       * @since 4.0.0
 379       *
 380       * @param string $name Property to unset.
 381       */
 382  	public function __unset( $name ) {
 383          unset( $this->$name );
 384      }
 385  
 386      /**
 387       * Adds data to the cache if it doesn't already exist.
 388       *
 389       * @since 2.0.0
 390       *
 391       * @uses WP_Object_Cache::_exists() Checks to see if the cache already has data.
 392       * @uses WP_Object_Cache::set()     Sets the data after the checking the cache
 393       *                                  contents existence.
 394       *
 395       * @param int|string $key    What to call the contents in the cache.
 396       * @param mixed      $data   The contents to store in the cache.
 397       * @param string     $group  Optional. Where to group the cache contents. Default 'default'.
 398       * @param int        $expire Optional. When to expire the cache contents. Default 0 (no expiration).
 399       * @return bool False if cache key and group already exist, true on success
 400       */
 401  	public function add( $key, $data, $group = 'default', $expire = 0 ) {
 402          if ( wp_suspend_cache_addition() ) {
 403              return false;
 404          }
 405  
 406          if ( empty( $group ) ) {
 407              $group = 'default';
 408          }
 409  
 410          $id = $key;
 411          if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
 412              $id = $this->blog_prefix . $key;
 413          }
 414  
 415          if ( $this->_exists( $id, $group ) ) {
 416              return false;
 417          }
 418  
 419          return $this->set( $key, $data, $group, (int) $expire );
 420      }
 421  
 422      /**
 423       * Sets the list of global cache groups.
 424       *
 425       * @since 3.0.0
 426       *
 427       * @param array $groups List of groups that are global.
 428       */
 429  	public function add_global_groups( $groups ) {
 430          $groups = (array) $groups;
 431  
 432          $groups              = array_fill_keys( $groups, true );
 433          $this->global_groups = array_merge( $this->global_groups, $groups );
 434      }
 435  
 436      /**
 437       * Decrements numeric cache item's value.
 438       *
 439       * @since 3.3.0
 440       *
 441       * @param int|string $key    The cache key to decrement.
 442       * @param int        $offset Optional. The amount by which to decrement the item's value. Default 1.
 443       * @param string     $group  Optional. The group the key is in. Default 'default'.
 444       * @return false|int False on failure, the item's new value on success.
 445       */
 446  	public function decr( $key, $offset = 1, $group = 'default' ) {
 447          if ( empty( $group ) ) {
 448              $group = 'default';
 449          }
 450  
 451          if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
 452              $key = $this->blog_prefix . $key;
 453          }
 454  
 455          if ( ! $this->_exists( $key, $group ) ) {
 456              return false;
 457          }
 458  
 459          if ( ! is_numeric( $this->cache[ $group ][ $key ] ) ) {
 460              $this->cache[ $group ][ $key ] = 0;
 461          }
 462  
 463          $offset = (int) $offset;
 464  
 465          $this->cache[ $group ][ $key ] -= $offset;
 466  
 467          if ( $this->cache[ $group ][ $key ] < 0 ) {
 468              $this->cache[ $group ][ $key ] = 0;
 469          }
 470  
 471          return $this->cache[ $group ][ $key ];
 472      }
 473  
 474      /**
 475       * Removes the contents of the cache key in the group.
 476       *
 477       * If the cache key does not exist in the group, then nothing will happen.
 478       *
 479       * @since 2.0.0
 480       *
 481       * @param int|string $key        What the contents in the cache are called.
 482       * @param string     $group      Optional. Where the cache contents are grouped. Default 'default'.
 483       * @param bool       $deprecated Optional. Unused. Default false.
 484       * @return bool False if the contents weren't deleted and true on success.
 485       */
 486  	public function delete( $key, $group = 'default', $deprecated = false ) {
 487          if ( empty( $group ) ) {
 488              $group = 'default';
 489          }
 490  
 491          if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
 492              $key = $this->blog_prefix . $key;
 493          }
 494  
 495          if ( ! $this->_exists( $key, $group ) ) {
 496              return false;
 497          }
 498  
 499          unset( $this->cache[ $group ][ $key ] );
 500          return true;
 501      }
 502  
 503      /**
 504       * Clears the object cache of all data.
 505       *
 506       * @since 2.0.0
 507       *
 508       * @return true Always returns true.
 509       */
 510  	public function flush() {
 511          $this->cache = array();
 512  
 513          return true;
 514      }
 515  
 516      /**
 517       * Retrieves the cache contents, if it exists.
 518       *
 519       * The contents will be first attempted to be retrieved by searching by the
 520       * key in the cache group. If the cache is hit (success) then the contents
 521       * are returned.
 522       *
 523       * On failure, the number of cache misses will be incremented.
 524       *
 525       * @since 2.0.0
 526       *
 527       * @param int|string $key    What the contents in the cache are called.
 528       * @param string     $group  Optional. Where the cache contents are grouped. Default 'default'.
 529       * @param bool       $force  Optional. Unused. Whether to force a refetch rather than relying on the local
 530       *                           cache. Default false.
 531       * @param bool       $found  Optional. Whether the key was found in the cache (passed by reference).
 532       *                           Disambiguates a return of false, a storable value. Default null.
 533       * @return false|mixed False on failure to retrieve contents or the cache contents on success.
 534       */
 535  	public function get( $key, $group = 'default', $force = false, &$found = null ) {
 536          if ( empty( $group ) ) {
 537              $group = 'default';
 538          }
 539  
 540          if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
 541              $key = $this->blog_prefix . $key;
 542          }
 543  
 544          if ( $this->_exists( $key, $group ) ) {
 545              $found             = true;
 546              $this->cache_hits += 1;
 547              if ( is_object( $this->cache[ $group ][ $key ] ) ) {
 548                  return clone $this->cache[ $group ][ $key ];
 549              } else {
 550                  return $this->cache[ $group ][ $key ];
 551              }
 552          }
 553  
 554          $found               = false;
 555          $this->cache_misses += 1;
 556          return false;
 557      }
 558  
 559      /**
 560       * Increments numeric cache item's value.
 561       *
 562       * @since 3.3.0
 563       *
 564       * @param int|string $key    The cache key to increment
 565       * @param int        $offset Optional. The amount by which to increment the item's value. Default 1.
 566       * @param string     $group  Optional. The group the key is in. Default 'default'.
 567       * @return false|int False on failure, the item's new value on success.
 568       */
 569  	public function incr( $key, $offset = 1, $group = 'default' ) {
 570          if ( empty( $group ) ) {
 571              $group = 'default';
 572          }
 573  
 574          if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
 575              $key = $this->blog_prefix . $key;
 576          }
 577  
 578          if ( ! $this->_exists( $key, $group ) ) {
 579              return false;
 580          }
 581  
 582          if ( ! is_numeric( $this->cache[ $group ][ $key ] ) ) {
 583              $this->cache[ $group ][ $key ] = 0;
 584          }
 585  
 586          $offset = (int) $offset;
 587  
 588          $this->cache[ $group ][ $key ] += $offset;
 589  
 590          if ( $this->cache[ $group ][ $key ] < 0 ) {
 591              $this->cache[ $group ][ $key ] = 0;
 592          }
 593  
 594          return $this->cache[ $group ][ $key ];
 595      }
 596  
 597      /**
 598       * Replaces the contents in the cache, if contents already exist.
 599       *
 600       * @since 2.0.0
 601       *
 602       * @see WP_Object_Cache::set()
 603       *
 604       * @param int|string $key    What to call the contents in the cache.
 605       * @param mixed      $data   The contents to store in the cache.
 606       * @param string     $group  Optional. Where to group the cache contents. Default 'default'.
 607       * @param int        $expire Optional. When to expire the cache contents. Default 0 (no expiration).
 608       * @return bool False if not exists, true if contents were replaced.
 609       */
 610  	public function replace( $key, $data, $group = 'default', $expire = 0 ) {
 611          if ( empty( $group ) ) {
 612              $group = 'default';
 613          }
 614  
 615          $id = $key;
 616          if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
 617              $id = $this->blog_prefix . $key;
 618          }
 619  
 620          if ( ! $this->_exists( $id, $group ) ) {
 621              return false;
 622          }
 623  
 624          return $this->set( $key, $data, $group, (int) $expire );
 625      }
 626  
 627      /**
 628       * Resets cache keys.
 629       *
 630       * @since 3.0.0
 631       *
 632       * @deprecated 3.5.0 Use switch_to_blog()
 633       * @see switch_to_blog()
 634       */
 635  	public function reset() {
 636          _deprecated_function( __FUNCTION__, '3.5.0', 'switch_to_blog()' );
 637  
 638          // Clear out non-global caches since the blog ID has changed.
 639          foreach ( array_keys( $this->cache ) as $group ) {
 640              if ( ! isset( $this->global_groups[ $group ] ) ) {
 641                  unset( $this->cache[ $group ] );
 642              }
 643          }
 644      }
 645  
 646      /**
 647       * Sets the data contents into the cache.
 648       *
 649       * The cache contents are grouped by the $group parameter followed by the
 650       * $key. This allows for duplicate ids in unique groups. Therefore, naming of
 651       * the group should be used with care and should follow normal function
 652       * naming guidelines outside of core WordPress usage.
 653       *
 654       * The $expire parameter is not used, because the cache will automatically
 655       * expire for each time a page is accessed and PHP finishes. The method is
 656       * more for cache plugins which use files.
 657       *
 658       * @since 2.0.0
 659       *
 660       * @param int|string $key    What to call the contents in the cache.
 661       * @param mixed      $data   The contents to store in the cache.
 662       * @param string     $group  Optional. Where to group the cache contents. Default 'default'.
 663       * @param int        $expire Not Used.
 664       * @return true Always returns true.
 665       */
 666  	public function set( $key, $data, $group = 'default', $expire = 0 ) {
 667          if ( empty( $group ) ) {
 668              $group = 'default';
 669          }
 670  
 671          if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
 672              $key = $this->blog_prefix . $key;
 673          }
 674  
 675          if ( is_object( $data ) ) {
 676              $data = clone $data;
 677          }
 678  
 679          $this->cache[ $group ][ $key ] = $data;
 680          return true;
 681      }
 682  
 683      /**
 684       * Echoes the stats of the caching.
 685       *
 686       * Gives the cache hits, and cache misses. Also prints every cached group,
 687       * key and the data.
 688       *
 689       * @since 2.0.0
 690       */
 691  	public function stats() {
 692          echo '<p>';
 693          echo "<strong>Cache Hits:</strong> {$this->cache_hits}<br />";
 694          echo "<strong>Cache Misses:</strong> {$this->cache_misses}<br />";
 695          echo '</p>';
 696          echo '<ul>';
 697          foreach ( $this->cache as $group => $cache ) {
 698              echo "<li><strong>Group:</strong> $group - ( " . number_format( strlen( serialize( $cache ) ) / KB_IN_BYTES, 2 ) . 'k )</li>';
 699          }
 700          echo '</ul>';
 701      }
 702  
 703      /**
 704       * Switches the internal blog ID.
 705       *
 706       * This changes the blog ID used to create keys in blog specific groups.
 707       *
 708       * @since 3.5.0
 709       *
 710       * @param int $blog_id Blog ID.
 711       */
 712  	public function switch_to_blog( $blog_id ) {
 713          $blog_id           = (int) $blog_id;
 714          $this->blog_prefix = $this->multisite ? $blog_id . ':' : '';
 715      }
 716  
 717      /**
 718       * Serves as a utility function to determine whether a key exists in the cache.
 719       *
 720       * @since 3.4.0
 721       *
 722       * @param int|string $key   Cache key to check for existence.
 723       * @param string     $group Cache group for the key existence check.
 724       * @return bool Whether the key exists in the cache for the given group.
 725       */
 726  	protected function _exists( $key, $group ) {
 727          return isset( $this->cache[ $group ] ) && ( isset( $this->cache[ $group ][ $key ] ) || array_key_exists( $key, $this->cache[ $group ] ) );
 728      }
 729  
 730      /**
 731       * Sets up object properties; PHP 5 style constructor.
 732       *
 733       * @since 2.0.8
 734       */
 735  	public function __construct() {
 736          $this->multisite   = is_multisite();
 737          $this->blog_prefix = $this->multisite ? get_current_blog_id() . ':' : '';
 738  
 739          /**
 740           * @todo This should be moved to the PHP4 style constructor, PHP5
 741           * already calls __destruct()
 742           */
 743          register_shutdown_function( array( $this, '__destruct' ) );
 744      }
 745  
 746      /**
 747       * Saves the object cache before object is completely destroyed.
 748       *
 749       * Called upon object destruction, which should be when PHP ends.
 750       *
 751       * @since 2.0.8
 752       *
 753       * @return true Always returns true.
 754       */
 755  	public function __destruct() {
 756          return true;
 757      }
 758  }


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