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[mediawiki.git] / includes / cache / CacheDependency.php

<?php
/**
 * Data caching with dependencies.
 *
 * 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
 */

/**
 * This class stores an arbitrary value along with its dependencies.
 * Users should typically only use DependencyWrapper::getValueFromCache(),
 * rather than instantiating one of these objects directly.
 * @ingroup Cache
 */
class DependencyWrapper {
        private $value;
        /** @var CacheDependency[] */
        private $deps;

        /**
         * Create an instance.
         * @param mixed $value The user-supplied value
         * @param CacheDependency|CacheDependency[] $deps A dependency or dependency
         *   array. All dependencies must be objects implementing CacheDependency.
         */
        function __construct( $value = false, $deps = array() ) {
                $this->value = $value;

                if ( !is_array( $deps ) ) {
                        $deps = array( $deps );
                }

                $this->deps = $deps;
        }

        /**
         * Returns true if any of the dependencies have expired
         *
         * @return bool
         */
        function isExpired() {
                foreach ( $this->deps as $dep ) {
                        if ( $dep->isExpired() ) {
                                return true;
                        }
                }

                return false;
        }

        /**
         * Initialise dependency values in preparation for storing. This must be
         * called before serialization.
         */
        function initialiseDeps() {
                foreach ( $this->deps as $dep ) {
                        $dep->loadDependencyValues();
                }
        }

        /**
         * Get the user-defined value
         * @return bool|mixed
         */
        function getValue() {
                return $this->value;
        }

        /**
         * Store the wrapper to a cache
         *
         * @param BagOStuff $cache
         * @param string $key
         * @param int $expiry
         */
        function storeToCache( $cache, $key, $expiry = 0 ) {
                $this->initialiseDeps();
                $cache->set( $key, $this, $expiry );
        }

        /**
         * Attempt to get a value from the cache. If the value is expired or missing,
         * it will be generated with the callback function (if present), and the newly
         * calculated value will be stored to the cache in a wrapper.
         *
         * @param BagOStuff $cache A cache object
         * @param string $key The cache key
         * @param int $expiry The expiry timestamp or interval in seconds
         * @param bool|callable $callback The callback for generating the value, or false
         * @param array $callbackParams The function parameters for the callback
         * @param array $deps The dependencies to store on a cache miss. Note: these
         *    are not the dependencies used on a cache hit! Cache hits use the stored
         *    dependency array.
         *
         * @return mixed The value, or null if it was not present in the cache and no
         *    callback was defined.
         */
        static function getValueFromCache( $cache, $key, $expiry = 0, $callback = false,
                $callbackParams = array(), $deps = array()
        ) {
                $obj = $cache->get( $key );

                if ( is_object( $obj ) && $obj instanceof DependencyWrapper && !$obj->isExpired() ) {
                        $value = $obj->value;
                } elseif ( $callback ) {
                        $value = call_user_func_array( $callback, $callbackParams );
                        # Cache the newly-generated value
                        $wrapper = new DependencyWrapper( $value, $deps );
                        $wrapper->storeToCache( $cache, $key, $expiry );
                } else {
                        $value = null;
                }

                return $value;
        }
}

/**
 * @ingroup Cache
 */
abstract class CacheDependency {
        /**
         * Returns true if the dependency is expired, false otherwise
         */
        abstract function isExpired();

        /**
         * Hook to perform any expensive pre-serialize loading of dependency values.
         */
        function loadDependencyValues() {
        }
}

/**
 * @ingroup Cache
 */
class FileDependency extends CacheDependency {
        private $filename;
        private $timestamp;

        /**
         * Create a file dependency
         *
         * @param string $filename The name of the file, preferably fully qualified
         * @param null|bool|int $timestamp The unix last modified timestamp, or false if the
         *        file does not exist. If omitted, the timestamp will be loaded from
         *        the file.
         *
         * A dependency on a nonexistent file will be triggered when the file is
         * created. A dependency on an existing file will be triggered when the
         * file is changed.
         */
        function __construct( $filename, $timestamp = null ) {
                $this->filename = $filename;
                $this->timestamp = $timestamp;
        }

        /**
         * @return array
         */
        function __sleep() {
                $this->loadDependencyValues();

                return array( 'filename', 'timestamp' );
        }

        function loadDependencyValues() {
                if ( is_null( $this->timestamp ) ) {
                        MediaWiki\suppressWarnings();
                        # Dependency on a non-existent file stores "false"
                        # This is a valid concept!
                        $this->timestamp = filemtime( $this->filename );
                        MediaWiki\restoreWarnings();
                }
        }

        /**
         * @return bool
         */
        function isExpired() {
                MediaWiki\suppressWarnings();
                $lastmod = filemtime( $this->filename );
                MediaWiki\restoreWarnings();
                if ( $lastmod === false ) {
                        if ( $this->timestamp === false ) {
                                # Still nonexistent
                                return false;
                        } else {
                                # Deleted
                                wfDebug( "Dependency triggered: {$this->filename} deleted.\n" );

                                return true;
                        }
                } else {
                        if ( $lastmod > $this->timestamp ) {
                                # Modified or created
                                wfDebug( "Dependency triggered: {$this->filename} changed.\n" );

                                return true;
                        } else {
                                # Not modified
                                return false;
                        }
                }
        }
}

/**
 * @ingroup Cache
 */
class GlobalDependency extends CacheDependency {
        private $name;
        private $value;

        function __construct( $name ) {
                $this->name = $name;
                $this->value = $GLOBALS[$name];
        }

        /**
         * @return bool
         */
        function isExpired() {
                if ( !isset( $GLOBALS[$this->name] ) ) {
                        return true;
                }

                return $GLOBALS[$this->name] != $this->value;
        }
}

/**
 * @ingroup Cache
 */
class ConstantDependency extends CacheDependency {
        private $name;
        private $value;

        function __construct( $name ) {
                $this->name = $name;
                $this->value = constant( $name );
        }

        /**
         * @return bool
         */
        function isExpired() {
                return constant( $this->name ) != $this->value;
        }
}