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<?php
/**
* Per-process memory cache for storing items.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
* http://www.gnu.org/copyleft/gpl.html
*
* @file
* @ingroup Cache
*/
use Wikimedia\Assert\Assert;
/**
* Handles a simple LRU key/value map with a maximum number of entries
*
* Use ProcessCacheLRU if hierarchical purging is needed or objects can become stale
*
* @see ProcessCacheLRU
* @ingroup Cache
* @since 1.23
*/
class MapCacheLRU {
/** @var array */
protected $cache = []; // (key => value)
protected $maxCacheKeys; // integer; max entries
/**
* @param int $maxKeys Maximum number of entries allowed (min 1).
* @throws Exception When $maxCacheKeys is not an int or not above zero.
*/
public function __construct( $maxKeys ) {
Assert::parameterType( 'integer', $maxKeys, '$maxKeys' );
Assert::parameter( $maxKeys > 0, '$maxKeys', 'must be above zero' );
$this->maxCacheKeys = $maxKeys;
}
/**
* @param array $values Key/value map in order of increasingly recent access
* @param int $maxKeys
* @return MapCacheLRU
* @since 1.30
*/
public static function newFromArray( array $values, $maxKeys ) {
$mapCache = new self( $maxKeys );
$mapCache->cache = ( count( $values ) > $maxKeys )
? array_slice( $values, -$maxKeys, null, true )
: $values;
return $mapCache;
}
/**
* @return array Key/value map in order of increasingly recent access
* @since 1.30
*/
public function toArray() {
return $this->cache;
}
/**
* Set a key/value pair.
* This will prune the cache if it gets too large based on LRU.
* If the item is already set, it will be pushed to the top of the cache.
*
* To reduce evictions due to one-off use of many new keys, $rank can be
* set to have keys start at the top of a bottom fraction of the list. A value
* of 3/8 means values start at the top of the bottom 3/8s of the list and are
* moved to the top of the list when accessed a second time.
*
* @param string $key
* @param mixed $value
* @param float $rank Bottom fraction of the list where keys start off [Default: 1.0]
* @return void
*/
public function set( $key, $value, $rank = 1.0 ) {
if ( $this->has( $key ) ) {
$this->ping( $key );
} elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
reset( $this->cache );
$evictKey = key( $this->cache );
unset( $this->cache[$evictKey] );
}
if ( $rank < 1.0 && $rank > 0 ) {
$offset = intval( $rank * count( $this->cache ) );
$this->cache = array_slice( $this->cache, 0, $offset, true )
+ [ $key => $value ]
+ array_slice( $this->cache, $offset, null, true );
} else {
$this->cache[$key] = $value;
}
}
/**
* Check if a key exists
*
* @param string $key
* @return bool
*/
public function has( $key ) {
if ( !is_int( $key ) && !is_string( $key ) ) {
throw new UnexpectedValueException(
__METHOD__ . ' called with invalid key. Must be string or integer.' );
}
return array_key_exists( $key, $this->cache );
}
/**
* Get the value for a key.
* This returns null if the key is not set.
* If the item is already set, it will be pushed to the top of the cache.
*
* @param string $key
* @return mixed Returns null if the key was not found
*/
public function get( $key ) {
if ( !$this->has( $key ) ) {
return null;
}
$this->ping( $key );
return $this->cache[$key];
}
/**
* @return array
* @since 1.25
*/
public function getAllKeys() {
return array_keys( $this->cache );
}
/**
* Get an item with the given key, producing and setting it if not found.
*
* If the callback returns false, then nothing is stored.
*
* @since 1.28
* @param string $key
* @param callable $callback Callback that will produce the value
* @param float $rank Bottom fraction of the list where keys start off [Default: 1.0]
* @return mixed The cached value if found or the result of $callback otherwise
*/
public function getWithSetCallback( $key, callable $callback, $rank = 1.0 ) {
if ( $this->has( $key ) ) {
$value = $this->get( $key );
} else {
$value = call_user_func( $callback );
if ( $value !== false ) {
$this->set( $key, $value, $rank );
}
}
return $value;
}
/**
* Clear one or several cache entries, or all cache entries
*
* @param string|array $keys
* @return void
*/
public function clear( $keys = null ) {
if ( $keys === null ) {
$this->cache = [];
} else {
foreach ( (array)$keys as $key ) {
unset( $this->cache[$key] );
}
}
}
/**
* Push an entry to the top of the cache
*
* @param string $key
*/
protected function ping( $key ) {
$item = $this->cache[$key];
unset( $this->cache[$key] );
$this->cache[$key] = $item;
}
}
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