Add a Task for the worker to check and possibly schedule and run.

        Returns True if task and its dependencies were successfully scheduled or completed before.

def add(self, task, multiprocess=False, processes=0):
        """
        Add a Task for the worker to check and possibly schedule and run.

        Returns True if task and its dependencies were successfully scheduled or completed before.
        """
        if self._first_task is None and hasattr(task, 'task_id'):
            self._first_task = task.task_id
        self.add_succeeded = True
        if multiprocess:
            queue = multiprocessing.Manager().Queue()
            pool = multiprocessing.Pool(processes=processes if processes > 0 else None)
        else:
            queue = DequeQueue()
            pool = SingleProcessPool()
        self._validate_task(task)
        pool.apply_async(check_complete, [task, queue])

        # we track queue size ourselves because len(queue) won't work for multiprocessing
        queue_size = 1
        try:
            seen = {task.task_id}
            while queue_size:
                current = queue.get()
                queue_size -= 1
                item, is_complete = current
                for next in self._add(item, is_complete):
                    if next.task_id not in seen:
                        self._validate_task(next)
                        seen.add(next.task_id)
                        pool.apply_async(check_complete, [next, queue])
                        queue_size += 1
        except (KeyboardInterrupt, TaskException):
            raise
        except Exception as ex:
            self.add_succeeded = False
            formatted_traceback = traceback.format_exc()
            self._log_unexpected_error(task)
            task.trigger_event(Event.BROKEN_TASK, task, ex)
            self._email_unexpected_error(task, formatted_traceback)
            raise
        finally:
            pool.close()
            pool.join()
        return self.add_succeeded