pocketmine\scheduler\AsyncTask::isFinished PHP Method

    public function isFinished() : bool
    {
        return $this->isFinished;
    }

 public function collectAsyncTask(AsyncTask $task)
 {
     if ($task->isFinished() and !$task->isCompleted()) {
         --$this->asyncTasks;
         $task->onCompletion(Server::getInstance());
         $task->setCompleted();
         unset($this->asyncTaskStorage[$task->getTaskId()]);
         return true;
     }
     return false;
 }