PoolCounter.php

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<?php
abstract class PoolCounter {
    /* Return codes */
    const LOCKED = 1; /* Lock acquired */
    const RELEASED = 2; /* Lock released */
    const DONE = 3; /* Another worker did the work for you */

    const ERROR = -1; /* Indeterminate error */
    const NOT_LOCKED = -2; /* Called release() with no lock held */
    const QUEUE_FULL = -3; /* There are already maxqueue workers on this lock */
    const TIMEOUT = -4; /* Timeout exceeded */
    const LOCK_HELD = -5; /* Cannot acquire another lock while you have one lock held */

    protected $key;
    protected $workers;
    protected $maxqueue;
    protected $timeout;

    protected function __construct( $conf, $type, $key ) {
        $this->key = $key;
        $this->workers = $conf['workers'];
        $this->maxqueue = $conf['maxqueue'];
        $this->timeout = $conf['timeout'];
    }

    public static function factory( $type, $key ) {
        global $wgPoolCounterConf;
        if ( !isset( $wgPoolCounterConf[$type] ) ) {
            return new PoolCounter_Stub;
        }
        $conf = $wgPoolCounterConf[$type];
        $class = $conf['class'];

        return new $class( $conf, $type, $key );
    }

    abstract public function acquireForMe();

    abstract public function acquireForAnyone();

    abstract public function release();
}

class PoolCounter_Stub extends PoolCounter {
    public function __construct() {
        /* No parameters needed */
    }

    public function acquireForMe() {
        return Status::newGood( PoolCounter::LOCKED );
    }

    public function acquireForAnyone() {
        return Status::newGood( PoolCounter::LOCKED );
    }

    public function release() {
        return Status::newGood( PoolCounter::RELEASED );
    }
}

abstract class PoolCounterWork {
    protected $cacheable = false; //Does this override getCachedWork() ?

    public function __construct( $type, $key ) {
        $this->poolCounter = PoolCounter::factory( $type, $key );
    }

    abstract public function doWork();

    public function getCachedWork() {
        return false;
    }

    public function fallback() {
        return false;
    }

    function error( $status ) {
        return false;
    }

    function logError( $status ) {
        wfDebugLog( 'poolcounter', $status->getWikiText() );
    }

    public function execute( $skipcache = false ) {
        if ( $this->cacheable && !$skipcache ) {
            $status = $this->poolCounter->acquireForAnyone();
        } else {
            $status = $this->poolCounter->acquireForMe();
        }

        if ( !$status->isOK() ) {
            // Respond gracefully to complete server breakage: just log it and do the work
            $this->logError( $status );
            return $this->doWork();
        }

        switch ( $status->value ) {
            case PoolCounter::LOCKED:
                $result = $this->doWork();
                $this->poolCounter->release();
                return $result;

            case PoolCounter::DONE:
                $result = $this->getCachedWork();
                if ( $result === false ) {
                    /* That someone else work didn't serve us.
                     * Acquire the lock for me
                     */
                    return $this->execute( true );
                }
                return $result;

            case PoolCounter::QUEUE_FULL:
            case PoolCounter::TIMEOUT:
                $result = $this->fallback();

                if ( $result !== false ) {
                    return $result;
                }
                /* no break */

            /* These two cases should never be hit... */
            case PoolCounter::ERROR:
            default:
                $errors = array(
                    PoolCounter::QUEUE_FULL => 'pool-queuefull',
                    PoolCounter::TIMEOUT => 'pool-timeout' );

                $status = Status::newFatal( isset( $errors[$status->value] )
                    ? $errors[$status->value]
                    : 'pool-errorunknown' );
                $this->logError( $status );
                return $this->error( $status );
        }
    }
}

class PoolCounterWorkViaCallback extends PoolCounterWork {
    protected $doWork;
    protected $doCachedWork;
    protected $fallback;
    protected $error;

    public function __construct( $type, $key, array $callbacks ) {
        parent::__construct( $type, $key );
        foreach ( array( 'doWork', 'doCachedWork', 'fallback', 'error' ) as $name ) {
            if ( isset( $callbacks[$name] ) ) {
                if ( !is_callable( $callbacks[$name] ) ) {
                    throw new MWException( "Invalid callback provided for '$name' function." );
                }
                $this->$name = $callbacks[$name];
            }
        }
        if ( !isset( $this->doWork ) ) {
            throw new MWException( "No callback provided for 'doWork' function." );
        }
        $this->cacheable = isset( $this->doCachedWork );
    }

    public function doWork() {
        return call_user_func_array( $this->doWork, array() );
    }

    public function getCachedWork() {
        if ( $this->doCachedWork ) {
            return call_user_func_array( $this->doCachedWork, array() );
        }
        return false;
    }

    function fallback() {
        if ( $this->fallback ) {
            return call_user_func_array( $this->fallback, array() );
        }
        return false;
    }

    function error( $status ) {
        if ( $this->error ) {
            return call_user_func_array( $this->error, array( $status ) );
        }
        return false;
    }
}