src/pubcontrolclient.php
public function publish_async($channel, $item, $callback=null)
    {
        if (!$this->is_async_supported())
            throw new \RuntimeException('Asynchronous publishing not supported. '
                    . 'Recompile PHP with --enable-maintainer-zts to ' 
                    . 'turn pthreads on.');
        $this->tsclient->publish_async($channel, $item, $callback);
    }
public function publish_async($channel, $item, $callback=null)
    {
        if (!$this->is_async_supported())
            throw new \RuntimeException('Asynchronous publishing not supported. '
                    . 'Recompile PHP with --enable-maintainer-zts to ' 
                    . 'turn pthreads on.');
        $this->tsclient->publish_async($channel, $item, $callback);
    }
complete.