PoolCounter.php

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<?php
abstract class PoolCounter {
    /* Return codes */
    public const LOCKED = 1; /* Lock acquired */
    public const RELEASED = 2; /* Lock released */
    public const DONE = 3; /* Another worker did the work for you */
 
    public const ERROR = -1; /* Indeterminate error */
    public const NOT_LOCKED = -2; /* Called release() with no lock held */
    public const QUEUE_FULL = -3; /* There are already maxqueue workers on this lock */
    public const TIMEOUT = -4; /* Timeout exceeded */
    public const LOCK_HELD = -5; /* Cannot acquire another lock while you have one lock held */
 
    protected $key;
    protected $workers;
    protected $slots = 0;
    protected $maxqueue;
    protected $timeout;
 
    private $isMightWaitKey;
    private static $acquiredMightWaitKey = 0;
 
    private $fastStale;
 
    protected function __construct( array $conf, string $type, string $key ) {
        $this->workers = $conf['workers'];
        $this->maxqueue = $conf['maxqueue'];
        $this->timeout = $conf['timeout'];
        if ( isset( $conf['slots'] ) ) {
            $this->slots = $conf['slots'];
        }
        $this->fastStale = $conf['fastStale'] ?? false;
 
        if ( $this->slots ) {
            $key = $this->hashKeyIntoSlots( $type, $key, $this->slots );
        }
 
        $this->key = $key;
        $this->isMightWaitKey = !preg_match( '/^nowait:/', $this->key );
    }
 
    public static function factory( string $type, string $key ) {
        global $wgPoolCounterConf;
        if ( !isset( $wgPoolCounterConf[$type] ) ) {
            return new PoolCounterNull;
        }
        $conf = $wgPoolCounterConf[$type];
        $class = $conf['class'];
 
        return new $class( $conf, $type, $key );
    }
 
    public function getKey() {
        return $this->key;
    }
 
    abstract public function acquireForMe( $timeout = null );
 
    abstract public function acquireForAnyone( $timeout = null );
 
    abstract public function release();
 
    final protected function precheckAcquire() {
        if ( $this->isMightWaitKey ) {
            if ( self::$acquiredMightWaitKey ) {
                /*
                 * The poolcounter itself is quite happy to allow you to wait
                 * on another lock while you have a lock you waited on already
                 * but we think that it is unlikely to be a good idea.  So we
                 * made it an error.  If you are _really_ _really_ sure it is a
                 * good idea then feel free to implement an unsafe flag or
                 * something.
                 */
                return Status::newFatal( 'poolcounter-usage-error',
                    'You may only aquire a single non-nowait lock.' );
            }
        } elseif ( $this->timeout !== 0 ) {
            return Status::newFatal( 'poolcounter-usage-error',
                'Locks starting in nowait: must have 0 timeout.' );
        }
        return Status::newGood();
    }
 
    final protected function onAcquire() {
        self::$acquiredMightWaitKey |= $this->isMightWaitKey;
    }
 
    final protected function onRelease() {
        self::$acquiredMightWaitKey &= !$this->isMightWaitKey;
    }
 
    protected function hashKeyIntoSlots( $type, $key, $slots ) {
        return $type . ':' . ( hexdec( substr( sha1( $key ), 0, 4 ) ) % $slots );
    }
 
    public function isFastStaleEnabled() {
        return $this->fastStale;
    }
}