【八】协程停止
future对象有几个状态：
Pending
Running
Done
Cancelled
创建future的时候，task为pending，事件循环调用执行的时候当然就是running，调用完毕自然就是done，如果需要停止事件循环，就需要先把task取消。可以使用asyncio.Task获取事件循环的task
例如：
import asyncioimport timenow = lambda: time.time()async def do_some_work(x):print('Waiting: ', x)await asyncio.sleep(x)return 'Done after {}s'.format(x)coroutine1 = do_some_work(1)coroutine2 = do_some_work(2)coroutine3 = do_some_work(4)tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]start = now()loop = asyncio.get_event_loop()try:loop.run_until_complete(asyncio.wait(tasks))except KeyboardInterrupt as e:print(asyncio.Task.all_tasks())for task in asyncio.Task.all_tasks():print(task.cancel())loop.stop()loop.run_forever()finally:loop.close()print('TIME: ', now() - start)
启动事件循环之后，马上ctrl+c，会触发run_until_complete的执行异常 KeyBorardInterrupt。然后通过循环asyncio.Task取消future
True表示cannel成功，loop stop之后还需要再次开启事件循环，最后在close，不然会报错。
循环task，逐个cancel是一种方案，可是正如上面我们把task的列表封装在main函数中，main函数外进行事件循环的调用。这个时候，main相当于最外出的一个task，那么处理包装的main函数即可。
import asyncioimport timenow = lambda: time.time()async def do_some_work(x):print('Waiting: ', x)await asyncio.sleep(x)return 'Done after {}s'.format(x)async def main():coroutine1 = do_some_work(1)coroutine2 = do_some_work(2)coroutine3 = do_some_work(4)tasks = [asyncio.ensure_future(coroutine1),asyncio.ensure_future(coroutine2),asyncio.ensure_future(coroutine3)]done, pending = await asyncio.wait(tasks)for task in done:print('Task ret: ', task.result())start = now()loop = asyncio.get_event_loop()task = asyncio.ensure_future(main())try:loop.run_until_complete(task)except KeyboardInterrupt as e:print(asyncio.Task.all_tasks())print(asyncio.gather(*asyncio.Task.all_tasks()).cancel())loop.stop()loop.run_forever()finally:loop.close()
【九】不同线程的事件循环
很多时候，我们的事件循环用于注册协程，而有的协程需要动态的添加到事件循环中。一个简单的方式就是使用多线程。当前线程创建一个事件循环，然后在新建一个线程，在新线程中启动事件循环。当前线程不会被block。
import asyncioimport timenow = lambda: time.time()from threading import Threaddef start_loop(loop):asyncio.set_event_loop(loop)loop.run_forever()def more_work(x):print('More work {}'.format(x))time.sleep(x)print('Finished more work {}'.format(x))start = now()new_loop = asyncio.new_event_loop()t = Thread(target=start_loop, args=(new_loop,))t.start()print('TIME: {}'.format(time.time() - start))new_loop.call_soon_threadsafe(more_work, 6)new_loop.call_soon_threadsafe(more_work, 3)启动上述代码之后，当前线程不会被block，新线程中会按照顺序执行call_soon_threadsafe方法注册的more_work方法，后者因为time.sleep操作是同步阻塞的，因此运行完毕more_work需要大致6 + 3
【十】新线程协程
新线程协程的话，可以在主线程中创建一个new_loop，然后在另外的子线程中开启一个无限事件循环。主线程通过run_coroutine_threadsafe新注册协程对象。这样就能在子线程中进行事件循环的并发操作，同时主线程又不会被block。一共执行的时间大概在6s左右。
import asyncioimport timenow = lambda: time.time()from threading import Threaddef start_loop(loop):asyncio.set_event_loop(loop)loop.run_forever()async def do_some_work(x):print('Waiting {}'.format(x))await asyncio.sleep(x)print('Done after {}s'.format(x))def more_work(x):print('More work {}'.format(x))time.sleep(x)print('Finished more work {}'.format(x))start = now()new_loop = asyncio.new_event_loop()t = Thread(target=start_loop, args=(new_loop,))t.start()print('TIME: {}'.format(time.time() - start))asyncio.run_coroutine_threadsafe(do_some_work(6), new_loop)asyncio.run_coroutine_threadsafe(do_some_work(4), new_loop)
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