使用 asyncio 时，如何让所有正在运行的任务在关闭事件循环之前完成

问题描述：

我有以下代码:

@asyncio.coroutine
def do_something_periodically():
    while True:
        asyncio.async(my_expensive_operation())
        yield from asyncio.sleep(my_interval)
        if shutdown_flag_is_set:
            print("Shutting down")
            break

我运行这个函数直到完成.设置关闭时会出现问题 - 函数完成并且任何挂起的任务都不会运行.

I run this function until complete. The problem occurs when shutdown is set - the function completes and any pending tasks are never run.

这是错误:

task: <Task pending coro=<report() running at script.py:33> wait_for=<Future pending cb=[Task._wakeup()]>>

如何正确安排关机时间?

How do I schedule a shutdown correctly?

为了提供一些上下文，我正在编写一个系统监视器，它每 5 秒从/proc/stat 读取一次，计算该期间的 CPU 使用率，然后将结果发送到服务器.我想一直调度这些监控作业，直到我收到 sigterm，当我停止调度时，等待所有当前作业完成，然后优雅地退出.

To give some context, I'm writing a system monitor which reads from /proc/stat every 5 seconds, computes the cpu usage in that period, and then sends the result to a server. I want to keep scheduling these monitoring jobs until I receive sigterm, when I stop scheduling, wait for all current jobs to finish, and exit gracefully.

答

您可以检索未完成的任务并再次运行循环直到它们完成，然后关闭循环或退出您的程序.

You can retrieve unfinished tasks and run the loop again until they finished, then close the loop or exit your program.

pending = asyncio.all_tasks()
loop.run_until_complete(asyncio.gather(*pending))

pending 是待处理任务的列表.
asyncio.gather() 允许同时等待多个任务.

pending is a list of pending tasks.
asyncio.gather() allows to wait on several tasks at once.

如果你想确保所有的任务都在一个协程内完成(也许你有一个主"协程)，你可以这样做，例如:

If you want to ensure all the tasks are completed inside a coroutine (maybe you have a "main" coroutine), you can do it this way, for instance:

async def do_something_periodically():
    while True:
        asyncio.create_task(my_expensive_operation())
        await asyncio.sleep(my_interval)
        if shutdown_flag_is_set:
            print("Shutting down")
            break

    await asyncio.gather(*asyncio.all_tasks())

此外，在这种情况下，由于所有任务都是在同一个协程中创建的，因此您已经可以访问这些任务:

Also, in this case, since all the tasks are created in the same coroutine, you already have access to the tasks:

async def do_something_periodically():
    tasks = []
    while True:
        tasks.append(asyncio.create_task(my_expensive_operation()))
        await asyncio.sleep(my_interval)
        if shutdown_flag_is_set:
            print("Shutting down")
            break

    await asyncio.gather(*tasks)

使用 asyncio 时，如何让所有正在运行的任务在关闭事件循环之前完成

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