python——asyncio模块实现协程、异步编程（二）

【六】协程并发

定义tasks时可以设置多个ensure，也可以像多线程那样用append方法实现

tasks = [    asyncio.ensure_future(coroutine1),    asyncio.ensure_future(coroutine2),    asyncio.ensure_future(coroutine3)]for i in range(4, 6):      tasks.append(asyncio.ensure_future(do_some_work(i)))

当遇到阻塞时可以使用await让其他协程继续工作

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(3) tasks = [    asyncio.ensure_future(coroutine1),    asyncio.ensure_future(coroutine2),    asyncio.ensure_future(coroutine3)]for i in range(4, 6):      tasks.append(asyncio.ensure_future(do_some_work(i))) loop = asyncio.get_event_loop()start = now()loop.run_until_complete(asyncio.wait(tasks)) for task in tasks:    print('Task ret: ', task.result()) print('TIME: ', now() - start)

通过运行时间可以看出aysncio实现了并发。asyncio.wait(tasks) 也可以使用 asyncio.gather(*tasks) ,前者接受一个task列表，后者接收一堆task。

【七】协程嵌套

使用async可以定义协程，协程用于耗时的io操作，我们也可以封装更多的io操作过程，这样就实现了嵌套的协程，即一个协程中await了另外一个协程，如此连接起来。

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) 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)    ]     dones, pendings = await asyncio.wait(tasks)     for task in dones:        print('Task ret: ', task.result()) start = now() loop = asyncio.get_event_loop()loop.run_until_complete(main()) print('TIME: ', now() - start)

如果使用的是 asyncio.gather创建协程对象，那么await的返回值就是协程运行的结果。

    #dones, pendings = await asyncio.wait(tasks)        #for task in dones:        #print('Task ret: ', task.result())    results = await asyncio.gather(*tasks)    for result in results:        print('Task ret: ', result)

不在main协程函数里处理结果，直接返回await的内容，那么最外层的run_until_complete将会返回main协程的结果。

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)    ]     return await asyncio.gather(*tasks) start = now()loop = asyncio.get_event_loop()results = loop.run_until_complete(main())for result in results:    print('Task ret: ', result) print('TIME: ', now() - start)

或者返回使用asyncio.wait方式挂起协程。

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)    ]     return await asyncio.wait(tasks) start = now() loop = asyncio.get_event_loop()done, pending = loop.run_until_complete(main()) for task in done:    print('Task ret: ', task.result()) print('TIME: ', now() - start)

也可以使用asyncio的as_completed方法

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)    ]    for task in asyncio.as_completed(tasks):        result = await task        print('Task ret: {}'.format(result)) start = now() loop = asyncio.get_event_loop()done = loop.run_until_complete(main())print('TIME: ', now() - start)

由此可见，协程的调用和组合十分的灵活，我们可以发挥想象尽情的浪