python - 使用 asyncio.wait 在任务异常后重试任务

Question

我有多个应该同时运行的协同程序，其中一些可能会抛出异常。在这些情况下，协程应该再次运行。我该如何做到这一点？我正在尝试做的最小演示:

import asyncio
import time

t = time.time()


async def c1():
    print("finished c1 {}".format(time.time() - t))


async def c2():
    await asyncio.sleep(3)
    print("finished c2 {}".format(time.time() - t))


called = False


async def c3():
    global called
    # raises an exception the first time it's called
    if not called:
        called = True
        raise RuntimeError("c3 called the first time")
    print("finished c3 {}".format(time.time() - t))


async def run():
    pending = {c1(), c2(), c3()}

    num_times_called = 0
    while pending:
        num_times_called += 1
        print("{} times called with {} pending tasks: {}".format(num_times_called, len(pending), pending))

        finished, pending = await asyncio.wait(pending, return_when=asyncio.FIRST_EXCEPTION)
        for task in finished:
            if task.exception():
                print("{} got an exception {}, retrying".format(task, task.exception()))
                pending.add(task)

        print("finished {}".format(finished))

    print("finished all {}".format(time.time() - t))


asyncio.get_event_loop().run_until_complete(run())

c3()表示某些协程将失败并需要重新运行。演示的问题是已完成的任务已完成并设置了异常，因此当我将其放回待定集时，下一个运行循环会立即退出而不会重新运行 c3()因为它已经完成了。

有没有办法清除任务以便它运行c3()再次？我知道附加到任务的协程实例不能再等待，否则我得到

RuntimeError('cannot reuse already awaited coroutine',)

这意味着我必须手动管理从协程实例到生成它的协程的映射，然后使用 task._coro 检索失败的协程实例- 这样对吗？

Answer 1

编辑:任务本身可能是 map 中的关键，这样更清晰。

async def run():
    tasks = {asyncio.ensure_future(c()): c for c in (c1, c2, c3)}
    pending = set(tasks.keys())

    num_times_called = 0
    while pending:
        num_times_called += 1
        print("{} times called with {} pending tasks: {}".format(num_times_called, len(pending), pending))

        finished, pending = await asyncio.wait(pending, return_when=asyncio.FIRST_EXCEPTION)
        for task in finished:
            if task.exception():
                print("{} got an exception {}, retrying".format(task, task.exception()))
                coro = tasks[task]
                new_task = asyncio.ensure_future(coro())
                tasks[new_task] = coro
                pending.add(new_task)

        print("finished {}".format(finished))

    print("finished all {}".format(time.time() - t))