如何将协程添加到正在运行的 asyncio 循环中？

Question

如何将新的协程添加到正在运行的 asyncio 循环中？ IE。一个已经在执行一组协程的程序。

我想作为一种解决方法，可以等待现有协程完成，然后初始化一个新循环（使用额外的协程）。但是有没有更好的方法？

Answer 1

您可以使用create_task 来调度新的协程：

import asyncio

async def cor1():
    ...

async def cor2():
    ...

async def main(loop):
    await asyncio.sleep(0)
    t1 = loop.create_task(cor1())
    await cor2()
    await t1

loop = asyncio.get_event_loop()
loop.run_until_complete(main(loop))
loop.close()

Answer 2

要将函数添加到已经运行的事件循环中，您可以使用：

asyncio.ensure_future(my_coro())

在我的例子中，我使用多线程 (threading) 和 asyncio 并希望将任务添加到已经运行的事件循环中。对于处于相同情况的任何其他人，请务必明确声明事件循环（因为在 Thread 中不存在事件循环）。即：

在全球范围内：

event_loop = asyncio.get_event_loop()

然后，在你的Thread：

asyncio.ensure_future(my_coro(), loop=event_loop)

Answer 3

您的问题非常接近“如何向正在运行的程序添加函数调用？”

什么时候需要向事件循环中添加新的协程？

让我们看一些例子。这里程序使用两个协程并行启动事件循环：

import asyncio
from random import randint


async def coro1():
    res = randint(0,3)
    await asyncio.sleep(res)
    print('coro1 finished with output {}'.format(res))
    return res

async def main():
    await asyncio.gather(
        coro1(),
        coro1()
    ) # here we have two coroutines running parallely

if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())

输出：

coro1 finished with output 1
coro1 finished with output 2
[Finished in 2.2s]

您可能需要添加一些协程来获取coro1 的结果并在它准备好后立即使用它？在这种情况下，只需创建等待 coro1 的协程并使用它的返回值：

import asyncio
from random import randint


async def coro1():
    res = randint(0,3)
    await asyncio.sleep(res)
    print('coro1 finished with output {}'.format(res))
    return res

async def coro2():
    res = await coro1()
    res = res * res
    await asyncio.sleep(res)
    print('coro2 finished with output {}'.format(res))
    return res

async def main():
    await asyncio.gather(
        coro2(),
        coro2()
    ) # here we have two coroutines running parallely

if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(main())

输出：

coro1 finished with output 1
coro2 finished with output 1
coro1 finished with output 3
coro2 finished with output 9
[Finished in 12.2s]

将协程视为具有特定语法的常规函数​​。您可以启动一组函数并行执行（asyncio.gather），您可以在第一次完成后启动下一个函数，您可以创建调用其他函数的新函数。

Answer 4

这里的答案似乎都没有完全回答这个问题。通过让“父”任务为您完成任务，可以将任务添加到正在运行的事件循环中。我不确定确保父母在孩子全部完成之前不会结束的最pythonic方法是什么（假设这是您想要的行为），但这确实有效。

import asyncio
import random


async def add_event(n):
    print('starting ' + str(n))
    await asyncio.sleep(n)
    print('ending ' + str(n))
    return n


async def main(loop):

    added_tasks = []

    delays = list(range(5))

    # shuffle to simulate unknown run times
    random.shuffle(delays)

    for n in delays:
        print('adding ' + str(n))
        task = loop.create_task(add_event(n))
        added_tasks.append(task)
        await asyncio.sleep(0)

    print('done adding tasks')

    results = await asyncio.gather(*added_tasks)
    print('done running tasks')

    return results


loop = asyncio.get_event_loop()
results = loop.run_until_complete(main(loop))
print(results)

Answer 5

如果任务是将协程添加到已经在执行一些协程的循环中，那么你可以使用我的这个解决方案

import asyncio
import time
from threading import Thread

from random import randint


# first, we need a loop running in a parallel Thread
class AsyncLoopThread(Thread):
    def __init__(self):
        super().__init__(daemon=True)
        self.loop = asyncio.new_event_loop()

    def run(self):
        asyncio.set_event_loop(self.loop)
        self.loop.run_forever()


# example coroutine
async def coroutine(num, sec):
    await asyncio.sleep(sec)
    print(f'Coro {num} has finished')


if __name__ == '__main__':
    # init a loop in another Thread
    loop_handler = AsyncLoopThread()
    loop_handler.start()

    # adding first 5 coros
    for i in range(5):
        print(f'Add Coro {i} to the loop')
        asyncio.run_coroutine_threadsafe(coroutine(i, randint(3, 5)), loop_handler.loop)

    time.sleep(3)
    print('Adding 5 more coros')

    # adding 5 more coros
    for i in range(5, 10):
        print(f'Add Coro {i} to the loop')
        asyncio.run_coroutine_threadsafe(coroutine(i, randint(3, 5)), loop_handler.loop)

    # let them all finish
    time.sleep(60)
    

执行完这个例子后，我们会得到这样的输出：

Add Coro 0 to the loop
Add Coro 1 to the loop
Add Coro 2 to the loop
Add Coro 3 to the loop
Add Coro 4 to the loop
Coro 0 has finished
Adding 5 more coros
Add Coro 5 to the loop
Add Coro 6 to the loop
Add Coro 7 to the loop
Add Coro 8 to the loop
Add Coro 9 to the loop
Coro 1 has finished
Coro 3 has finished
Coro 2 has finished
Coro 4 has finished
Coro 9 has finished
Coro 5 has finished
Coro 7 has finished
Coro 6 has finished
Coro 8 has finished

Process finished with exit code 0