API * Optimized backlinking query (still needs an index change)

[mediawiki.git] / includes / CacheDependency.php

<?php

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

        /**
         * Create an instance.
         * @param mixed $value The user-supplied value
         * @param mixed $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
         */
        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
         */
        function getValue() {
                return $this->value;
        }

        /**
         * Store the wrapper to a cache
         */
        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 object $cache A cache object such as $wgMemc
         * @param string $key The cache key
         * @param integer $expiry The expiry timestamp or interval in seconds
         * @param mixed $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;
        }
}

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() {}
}

class FileDependency extends CacheDependency {
        var $filename, $timestamp;

        /**
         * Create a file dependency
         *
         * @param string $filename The name of the file, preferably fully qualified
         * @param mixed $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;
        }

        function loadDependencyValues() {
                if ( is_null( $this->timestamp ) ) {
                        if ( !file_exists( $this->filename ) ) {
                                # Dependency on a non-existent file
                                # This is a valid concept!
                                $this->timestamp = false;
                        } else {
                                $this->timestamp = filemtime( $this->filename );
                        }
                }
        }

        function isExpired() {
                if ( !file_exists( $this->filename ) ) {
                        if ( $this->timestamp === false ) {
                                # Still nonexistent
                                return false;
                        } else {
                                # Deleted
                                wfDebug( "Dependency triggered: {$this->filename} deleted.\n" );
                                return true;
                        }
                } else {
                        $lastmod = filemtime( $this->filename );
                        if ( $lastmod > $this->timestamp ) {
                                # Modified or created
                                wfDebug( "Dependency triggered: {$this->filename} changed.\n" );
                                return true;
                        } else {
                                # Not modified
                                return false;
                        }
                }
        }
}

class TitleDependency extends CacheDependency {
        var $titleObj;
        var $ns, $dbk;
        var $touched;

        /**
         * Construct a title dependency
         * @param Title $title
         */
        function __construct( Title $title ) {
                $this->titleObj = $title;
                $this->ns = $title->getNamespace();
                $this->dbk = $title->getDBkey();
        }

        function loadDependencyValues() {
                $this->touched = $this->getTitle()->getTouched();
        }
        
        /**
         * Get rid of bulky Title object for sleep
         */
        function __sleep() {
                return array( 'ns', 'dbk', 'touched' );
        }

        function getTitle() {
                if ( !isset( $this->titleObj ) ) {
                        $this->titleObj = Title::makeTitle( $this->ns, $this->dbk );
                } 
                return $this->titleObj;
        }

        function isExpired() {
                $touched = $this->getTitle()->getTouched();
                if ( $this->touched === false ) {
                        if ( $touched === false ) {
                                # Still missing
                                return false;
                        } else {
                                # Created
                                return true;
                        }
                } elseif ( $touched === false ) {
                        # Deleted
                        return true;
                } elseif ( $touched > $this->touched ) {
                        # Updated
                        return true;
                } else {
                        # Unmodified
                        return false;
                }
        }
}

class TitleListDependency extends CacheDependency {
        var $linkBatch;
        var $timestamps;
        
        /**
         * Construct a dependency on a list of titles
         */
        function __construct( LinkBatch $linkBatch ) {
                $this->linkBatch = $linkBatch;
        }

        function calculateTimestamps() {
                # Initialise values to false
                $timestamps = array();
                foreach ( $this->getLinkBatch()->data as $ns => $dbks ) {
                        if ( count( $dbks ) > 0 ) {
                                $timestamps[$ns] = array();
                                foreach ( $dbks as $dbk => $value ) {
                                        $timestamps[$ns][$dbk] = false;
                                }
                        }
                }

                # Do the query
                if ( count( $timestamps ) ) {
                        $dbr =& wfGetDB( DB_SLAVE );
                        $where = $this->getLinkBatch()->constructSet( 'page', $dbr );
                        $res = $dbr->select( 'page', 
                                array( 'page_namespace', 'page_title', 'page_touched' ),
                                $where, __METHOD__ );
                        while ( $row = $dbr->fetchObject( $res ) ) {
                                $timestamps[$row->page_namespace][$row->page_title] = $row->page_touched;
                        }
                }
                return $timestamps;
        }

        function loadDependencyValues() {
                $this->timestamps = $this->calculateTimestamps();
        }

        function __sleep() {
                return array( 'timestamps' );
        }

        function getLinkBatch() {
                if ( !isset( $this->linkBatch ) ){
                        $this->linkBatch = new LinkBatch;
                        $this->linkBatch->setArray( $this->timestamps );
                }
                return $this->linkBatch;
        }

        function isExpired() {
                $newTimestamps = $this->calculateTimestamps();
                foreach ( $this->timestamps as $ns => $dbks ) {
                        foreach ( $dbks as $dbk => $oldTimestamp ) {
                                $newTimestamp = $newTimestamps[$ns][$dbk];
                                if ( $oldTimestamp === false ) {
                                        if ( $newTimestamp === false ) {
                                                # Still missing
                                        } else {
                                                # Created
                                                return true;
                                        }
                                } elseif ( $newTimestamp === false ) {
                                        # Deleted
                                        return true;
                                } elseif ( $newTimestamp > $oldTimestamp ) {
                                        # Updated
                                        return true;
                                } else {
                                        # Unmodified
                                }
                        }
                }
                return false;
        }
}

class GlobalDependency extends CacheDependency {
        var $name, $value;
        
        function __construct( $name ) {
                $this->name = $name;
                $this->value = $GLOBALS[$name];
        }

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

class ConstantDependency extends CacheDependency {
        var $name, $value;

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

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

?>