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MapCacheLRU.php
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MapCacheLRU.php
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<?php
/**
* 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\LightweightObjectStore\ExpirationAwareness;
/**
* Store key-value entries in a size-limited in-memory LRU cache.
*
* The last-modification timestamp of entries is internally tracked so that callers can
* specify the maximum acceptable age of entries in calls to the has() method. As a convenience,
* the hasField(), getField(), and setField() methods can be used for entries that are field/value
* maps themselves; such fields will have their own internally tracked last-modification timestamp.
*
* @ingroup Cache
* @since 1.23
*/
class MapCacheLRU implements ExpirationAwareness {
/** @var array Map of (key => value) */
private $cache = [];
/** @var array Map of (key => (UNIX timestamp, (field => UNIX timestamp))) */
private $timestamps = [];
/** @var float Default entry timestamp if not specified */
private $epoch;
/** @var int Max number of entries */
private $maxCacheKeys;
/** @var float|null */
private $wallClockOverride;
/** @var float */
private const RANK_TOP = 1.0;
/** @var int Array key that holds the entry's main timestamp (flat key use) */
private const SIMPLE = 0;
/** @var int Array key that holds the entry's field timestamps (nested key use) */
private const FIELDS = 1;
/**
* @param int $maxKeys Maximum number of entries allowed (min 1)
*/
public function __construct( int $maxKeys ) {
if ( $maxKeys <= 0 ) {
throw new InvalidArgumentException( '$maxKeys must be above zero' );
}
$this->maxCacheKeys = $maxKeys;
// Use the current time as the default "as of" timestamp of entries
$this->epoch = $this->getCurrentTime();
}
/**
* @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 = self::RANK_TOP ) {
if ( $this->has( $key ) ) {
$this->ping( $key );
} elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
$evictKey = array_key_first( $this->cache );
unset( $this->cache[$evictKey] );
unset( $this->timestamps[$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;
}
$this->timestamps[$key] = [
self::SIMPLE => $this->getCurrentTime(),
self::FIELDS => []
];
}
/**
* Check if a key exists
*
* @param string|int $key
* @param float $maxAge Ignore items older than this many seconds [default: INF]
* @return bool
* @since 1.32 Added $maxAge
*/
public function has( $key, $maxAge = INF ) {
if ( !is_int( $key ) && !is_string( $key ) ) {
throw new UnexpectedValueException(
__METHOD__ . ': invalid key; must be string or integer.' );
}
return array_key_exists( $key, $this->cache )
&& (
// Optimization: Avoid expensive getAge/getCurrentTime for common case (T275673)
$maxAge === INF
|| $maxAge <= 0
|| $this->getKeyAge( $key ) <= $maxAge
);
}
/**
* 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
* @param float $maxAge Ignore items older than this many seconds [default: INF]
* @param mixed|null $default Value to return if no key is found [default: null]
* @return mixed Returns $default if the key was not found or is older than $maxAge
* @since 1.32 Added $maxAge
* @since 1.34 Added $default
*
* Although sometimes this can be tainted, taint-check doesn't distinguish separate instances
* of MapCacheLRU, so assume untainted to cut down on false positives. See T272134.
* @return-taint none
*/
public function get( $key, $maxAge = INF, $default = null ) {
if ( !$this->has( $key, $maxAge ) ) {
return $default;
}
$this->ping( $key );
return $this->cache[$key];
}
/**
* @param string|int $key
* @param string|int $field
* @param mixed $value
* @param float $initRank
*/
public function setField( $key, $field, $value, $initRank = self::RANK_TOP ) {
if ( $this->has( $key ) ) {
$this->ping( $key );
if ( !is_array( $this->cache[$key] ) ) {
$type = get_debug_type( $this->cache[$key] );
throw new UnexpectedValueException( "Cannot add field to non-array value ('$key' is $type)" );
}
} else {
$this->set( $key, [], $initRank );
}
if ( !is_string( $field ) && !is_int( $field ) ) {
throw new UnexpectedValueException(
__METHOD__ . ": invalid field for '$key'; must be string or integer." );
}
$this->cache[$key][$field] = $value;
$this->timestamps[$key][self::FIELDS][$field] = $this->getCurrentTime();
}
/**
* @param string|int $key
* @param string|int $field
* @param float $maxAge Ignore items older than this many seconds [default: INF]
* @return bool
* @since 1.32 Added $maxAge
*/
public function hasField( $key, $field, $maxAge = INF ) {
$value = $this->get( $key );
if ( !is_int( $field ) && !is_string( $field ) ) {
throw new UnexpectedValueException(
__METHOD__ . ": invalid field for '$key'; must be string or integer." );
}
return is_array( $value )
&& array_key_exists( $field, $value )
&& (
$maxAge === INF
|| $maxAge <= 0
|| $this->getKeyFieldAge( $key, $field ) <= $maxAge
);
}
/**
* @param string|int $key
* @param string|int $field
* @param float $maxAge Ignore items older than this many seconds [default: INF]
* @return mixed Returns null if the key was not found or is older than $maxAge
* @since 1.32 Added $maxAge
*/
public function getField( $key, $field, $maxAge = INF ) {
if ( !$this->hasField( $key, $field, $maxAge ) ) {
return null;
}
return $this->cache[$key][$field];
}
/**
* @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]
* @param float $maxAge Ignore items older than this many seconds [default: INF]
* @return mixed The cached value if found or the result of $callback otherwise
* @since 1.32 Added $maxAge
*/
public function getWithSetCallback(
$key, callable $callback, $rank = self::RANK_TOP, $maxAge = INF
) {
if ( $this->has( $key, $maxAge ) ) {
$value = $this->get( $key );
} else {
$value = $callback();
if ( $value !== false ) {
$this->set( $key, $value, $rank );
}
}
return $value;
}
/**
* Format a cache key string
*
* @since 1.41
* @param string|int ...$components Key components
* @return string
*/
public function makeKey( ...$components ) {
// Based on BagOStuff::makeKeyInternal, except without a required
// $keygroup prefix. While MapCacheLRU can and is used as cache for
// multiple groups of keys, it is equally common for the instance itself
// to represent a single group, and thus have keys where the first component
// can directly be a user-controlled variable.
$key = '';
foreach ( $components as $i => $component ) {
if ( $i > 0 ) {
$key .= ':';
}
$key .= strtr( $component, [ '%' => '%25', ':' => '%3A' ] );
}
return $key;
}
/**
* Clear one or several cache entries, or all cache entries
*
* @param string|int|array|null $keys
* @return void
*/
public function clear( $keys = null ) {
if ( func_num_args() == 0 ) {
$this->cache = [];
$this->timestamps = [];
} else {
foreach ( (array)$keys as $key ) {
unset( $this->cache[$key] );
unset( $this->timestamps[$key] );
}
}
}
/**
* Get the maximum number of keys allowed
*
* @return int
* @since 1.32
*/
public function getMaxSize() {
return $this->maxCacheKeys;
}
/**
* Resize the maximum number of cache entries, removing older entries as needed
*
* @param int $maxKeys Maximum number of entries allowed (min 1)
* @return void
* @since 1.32
*/
public function setMaxSize( int $maxKeys ) {
if ( $maxKeys <= 0 ) {
throw new InvalidArgumentException( '$maxKeys must be above zero' );
}
$this->maxCacheKeys = $maxKeys;
while ( count( $this->cache ) > $this->maxCacheKeys ) {
$evictKey = array_key_first( $this->cache );
unset( $this->cache[$evictKey] );
unset( $this->timestamps[$evictKey] );
}
}
/**
* Push an entry to the top of the cache
*
* @param string $key
*/
private function ping( $key ) {
$item = $this->cache[$key];
unset( $this->cache[$key] );
$this->cache[$key] = $item;
}
/**
* @param string|int $key
* @return float UNIX timestamp; the age of the given entry
*/
private function getKeyAge( $key ) {
$mtime = $this->timestamps[$key][self::SIMPLE] ?? $this->epoch;
return ( $this->getCurrentTime() - $mtime );
}
/**
* @param string|int $key
* @param string|int|null $field
* @return float UNIX timestamp; the age of the given entry field
*/
private function getKeyFieldAge( $key, $field ) {
$mtime = $this->timestamps[$key][self::FIELDS][$field] ?? $this->epoch;
return ( $this->getCurrentTime() - $mtime );
}
public function __serialize() {
return [
'entries' => $this->cache,
'timestamps' => $this->timestamps,
'maxCacheKeys' => $this->maxCacheKeys,
];
}
public function __unserialize( $data ) {
$this->cache = $data['entries'] ?? [];
$this->timestamps = $data['timestamps'] ?? [];
// Fallback needed for serializations prior to T218511
$this->maxCacheKeys = $data['maxCacheKeys'] ?? ( count( $this->cache ) + 1 );
$this->epoch = $this->getCurrentTime();
}
/**
* @return float UNIX timestamp
* @codeCoverageIgnore
*/
protected function getCurrentTime() {
return $this->wallClockOverride ?: microtime( true );
}
/**
* @param float|null &$time Mock UNIX timestamp for testing
* @codeCoverageIgnore
*/
public function setMockTime( &$time ) {
$this->wallClockOverride =& $time;
}
}

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Expires
Wed, Aug 19, 08:12 (2 w, 3 d ago)
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MapCacheLRU.php (11 KB)

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