ProcessCacheLRU.php

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<?php
class ProcessCacheLRU {
        protected $cache = array(); // (key => prop => value)

        protected $maxCacheKeys; // integer; max entries

        public function __construct( $maxKeys ) {
                if ( !is_int( $maxKeys ) || $maxKeys < 1 ) {
                        throw new MWException( __METHOD__ . " must be given an integer and >= 1" );
                }
                $this->maxCacheKeys = $maxKeys;
        }

        public function set( $key, $prop, $value ) {
                if ( isset( $this->cache[$key] ) ) {
                        $this->ping( $key ); // push to top
                } elseif ( count( $this->cache ) >= $this->maxCacheKeys ) {
                        reset( $this->cache );
                        unset( $this->cache[key( $this->cache )] );
                }
                $this->cache[$key][$prop] = $value;
        }

        public function has( $key, $prop ) {
                return isset( $this->cache[$key][$prop] );
        }

        public function get( $key, $prop ) {
                if ( isset( $this->cache[$key][$prop] ) ) {
                        $this->ping( $key ); // push to top
                        return $this->cache[$key][$prop];
                } else {
                        return null;
                }
        }

        public function clear( $keys = null ) {
                if ( $keys === null ) {
                        $this->cache = array();
                } else {
                        foreach ( (array)$keys as $key ) {
                                unset( $this->cache[$key] );
                        }
                }
        }

        protected function ping( $key ) {
                $item = $this->cache[$key];
                unset( $this->cache[$key] );
                $this->cache[$key] = $item;
        }
}