python——asyncio模块实现协程、异步编程（三）

【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 asyncio import time now = 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 Thread def 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 Thread def 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)