asyncio 学习

#事件循环+回调（驱动生成器）+epoll(IO多路复用)
#asyncio是python用于解决异步io编程的一整套解决方案
#tornado、gevent、twisted（scrapy， django channels）
#torando(实现web服务器)， django+flask(uwsgi, gunicorn+nginx)
#tornado可以直接部署， nginx+tornado

#使用asyncio
# import asyncio
# import time
# async def get_html(url):
#     print("start get url")
#     await asyncio.sleep(2)
#     print("end get url")
#
# if __name__ == "__main__":
#     start_time = time.time()
#     loop = asyncio.get_event_loop()
#     tasks = [get_html("http://www.imooc.com") for i in range(10)]
#     loop.run_until_complete(asyncio.wait(tasks))
#     print(time.time()-start_time)

#获取协程的返回值
# import asyncio
# import time
# from functools import partial #给函数添加参数
# async def get_html(url):
#     print("start get url")
#     await asyncio.sleep(2)
#     return "bobby"
#
# def callback(url, future):
#     print(url)
#     print("send email to bobby")
#
# if __name__ == "__main__":
#     start_time = time.time()
#     loop = asyncio.get_event_loop()
#     # get_future = asyncio.ensure_future(get_html("http://www.imooc.com"))
#     task = loop.create_task(get_html("http://www.imooc.com"))
#     task.add_done_callback(partial(callback, "http://www.imooc.com"))
#     loop.run_until_complete(task)
#     print(task.result())
#wait 和 gather
import asyncio
import time
async def get_html(url):
    print("start get url")
    await asyncio.sleep(2)
    print("end get url")

if __name__ == "__main__":
    start_time = time.time()
    loop = asyncio.get_event_loop()
    tasks = [get_html("http://www.imooc.com") for i in range(10)]
    # loop.run_until_complete(asyncio.gather(*tasks))
    # print(time.time()-start_time)

    #gather和wait的区别
    #gather更加high-level 可以分组运行，分组取消
    group1 = [get_html("http://projectsedu.com") for i in range(2)]
    group2 = [get_html("http://www.imooc.com") for i in range(2)]
    group1 = asyncio.gather(*group1)
    group2 = asyncio.gather(*group2)
    group2.cancel()
    loop.run_until_complete(asyncio.gather(group1, group2))
    print(time.time() - start_time)

• event_loop 事件循环：程序开启一个无限循环，把一些函数注册到事件循环上，当满足事件发生的时候，调用相应的协程函数

• coroutine 协程：协程对象，指一个使用async关键字定义的函数，它的调用不会立即执行函数，而是会返回一个协程对象。协程对象需要注册到事件循环，由事件循环调用。

• task 任务：一个协程对象就是一个原生可以挂起的函数，任务则是对协程进一步封装，其中包含了任务的各种状态

• future: 代表将来执行或没有执行的任务的结果。它和task上没有本质上的区别

• async/await 关键字：python3.5用于定义协程的关键字，async定义一个协程，await用于挂起阻塞的异步调用接口。

task取消和子协程调用原理

#1. run_until_complete
# import asyncio
# loop = asyncio.get_event_loop()
# loop.run_forever()
# loop.run_until_complete()

#1. loop会被放到future中
#2. 取消future(task)

# import asyncio
# import time
#
# async def get_html(sleep_times):
#     print("waiting")
#     await asyncio.sleep(sleep_times)
#     print("done after {}s".format(sleep_times))
#
#
# if __name__ == "__main__":
#     task1 = get_html(2)
#     task2 = get_html(3)
#     task3 = get_html(3)
#
#     tasks = [task1, task2, task3]
#
#     loop = asyncio.get_event_loop()
#
#     try:
#         loop.run_until_complete(asyncio.wait(tasks))
#     except KeyboardInterrupt as e:
#         all_tasks = asyncio.Task.all_tasks()
#         for task in all_tasks:
#             print("cancel task")
#             print(task.cancel())
#         loop.stop()
#         loop.run_forever()#必须添加，否则会有异常
#     finally:
#         loop.close()

#注册协程到loop中有两种方法
#1. 通过ensure_future/create_task
#2. await