asyncio 学习笔记：调用定时函数

本文是 https://pymotw.com/3/asyncio/scheduling.html 的学习笔记，强烈推荐直接阅读原文。

立马执行一个函数

call_soon 支持在下一次事件循环的迭代中执行提供的回调函数。回调函数只能传递位置参数，如果想指定关键字参数的话，可以使用 functools.partial 函数来辅助使用。

# asyncio_call_soon.py
import asyncio
import functools


def callback(arg, *, kwarg='default'):
    print('callback with {0} and {1}'.format(arg, kwarg))


async def main(loop):
    print('register callbacks')
    loop.call_soon(callback, 1)
    wrapped = functools.partial(callback, kwarg='not default')
    loop.call_soon(wrapped, 2)

    await asyncio.sleep(0.1)


event_loop = asyncio.get_event_loop()
try:
    print('entering event loop')
    event_loop.run_until_complete(main(event_loop))
finally:
    print('closing event loop')
    event_loop.close()

回调函数会按调度顺序执行:

$ python3.6 asyncio_call_soon.py
entering event loop
register callbacks
callback with 1 and default
callback with 2 and not default
closing event loop

延迟执行

可以使用 call_later 方法实现延迟多少秒后执行回调函数。call_later 的第一个参数是延迟多少秒，第二个参数是回调函数，后面的参数是回调函数的位置参数:

# asyncio_call_later.py
import asyncio


def callback(n):
    print('callback with {0}'.format(n))


async def main(loop):
    print('register callbacks')
    loop.call_later(0.2, callback, 1)
    loop.call_later(0.1, callback, 2)
    loop.call_soon(callback, 3)

    await asyncio.sleep(0.4)


event_loop = asyncio.get_event_loop()
try:
    print('entering event loop')
    event_loop.run_until_complete(main(event_loop))
finally:
    print('closing event loop')
    event_loop.close()

执行结果：

$ python3.6 asyncio_call_later.py
entering event loop
register callbacks
callback with 3
callback with 2
callback with 1
closing event loop

指定时间执行

可以使用 call_at 方法实现在将来指定的某个时间执行回调函数。call_at 的第一个参数是执行的时间点，第二个参数是回调函数，后面的参数是回调函数的位置参数。有一点需要注意的是不用使用 time 或 datetime 模块的时间点，要使用 loop.time() 获取当前时间。

# asyncio_call_at.py
import asyncio
import time


def callback(n, loop):
    print('callback with {0} at {1}'.format(n, loop.time()))


async def main(loop):
    now = loop.time()
    print('clock time: {0}'.format(time.time()))
    print('loop time: {0}'.format(now))

    print('register callbacks')
    loop.call_at(now + 0.2, callback, 1, loop)
    loop.call_at(now + 0.1, callback, 2, loop)
    loop.call_soon(callback, 3, loop)

    await asyncio.sleep(1)


event_loop = asyncio.get_event_loop()
try:
    print('entering event loop')
    event_loop.run_until_complete(main(event_loop))
finally:
    print('closing event loop')
    event_loop.close()

再次提醒，不要用 time.time() 来计算时间，而是应该使用 loop.time()，它们其实是不同的：

$ python3.6 asyncio_call_at.py
entering event loop
clock time: 1502272983.100926
loop time: 513773.744280748
register callbacks
callback with 3 at 513773.744416457
callback with 2 at 513773.848605754
callback with 1 at 513773.94877137
closing event loop

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