Update Codex from v1.20.0 to v1.20.1

[mediawiki.git] / includes / libs / MapCacheLRU.php

<?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
 */
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;
        }
}