python asyncio在带有回调的执行程序中运行

Question

我对异步编程和python很新，但我想在状态机中实现异步函数。要求如下：

1. 异步任务必须在任何时间点取消
2. 异步任务不得阻止执行的主线程
3. 异步任务必须在完成后调用回调。

为了达到目标1＆amp; 2，我已经成功地实现了我的异步例​​程，在这里所述的执行器内运行：asyncio: Is it possible to cancel a future been run by an Executor?。在调试时，我看到我也完成了＃2，因为原始线程继续成功。但是，我很难实现回调函数。请注意，此回调函数必须在原始线程上运行，因为它将更改分配给它的对象的状态。我怎么能做到这一点？

我的代码：

class Free(State):

    def write(self, manager):
        write_future = self.write_async(manager)
        self.set_write_future(write_future)         
        self.change_state(manager, busy_state)    

    def write_async(self, manager):
        event = threading.Event()
        write_future = asyncio.get_event_loop().run_in_executor(None, self.async_write, 10, event)
        write_future.add_done_callback(functools.partial(self.async_write_callback, manager))
        return event    

    def async_write(self, seconds_to_block, event):
        for i in range(seconds_to_block):
            if event.is_set():
                return
            print('writing {}/{}'.format(i, seconds_to_block))
            time.sleep(1)
        print('done writing {}'.format(seconds_to_block))

    def async_write_callback(self, manager):
        #never gets called
        self.terminate_future()
        self.change_state(manager, free_state)