protected function getCallable()
{
$callback = null;
if (is_object($this->runnable) && $this->runnable instanceof Runnable) {
$callback = array($this->runnable, 'run');
} elseif (is_callable($this->runnable)) {
$callback = $this->runnable;
} else {
$callback = array($this, 'run');
}
return $callback;
}