计算事件循环中的活动任务数 [英] Count active tasks in event loop

问题描述

如何找出事件循环中有多少活动任务？ 在文档中我只找到asyncio.Task.all_tasks()，但它是简单的递增计数器：

import asyncio


async def coro():
    await asyncio.sleep(1)


async def main():
    tasks = []
    print('Tasks count: ', len(asyncio.Task.all_tasks()))
    for idx in range(3):
        task = asyncio.ensure_future(coro())
        tasks.append(task)
        print('Tasks count: ', len(asyncio.Task.all_tasks()))
    await asyncio.gather(*tasks)
    print('Tasks count: ', len(asyncio.Task.all_tasks()))


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

输出：

Tasks count:  1
Tasks count:  2
Tasks count:  3
Tasks count:  4
Tasks count:  4

预期输出：

Tasks count:  1
Tasks count:  2
Tasks count:  3
Tasks count:  4
Tasks count:  1

推荐答案

all_tasks返回所有注册的任务，包括已完成的任务。您可以通过done()对任务进行过滤操作来获取活动的任务：

import asyncio


async def coro():
    await asyncio.sleep(1)


async def main():
    tasks = []
    print('Tasks count: ', len(asyncio.Task.all_tasks()))
    for idx in range(3):
        task = asyncio.ensure_future(coro())
        tasks.append(task)
        print('Tasks count: ', len(asyncio.Task.all_tasks()))
    await asyncio.gather(*tasks)
    print('Tasks count: ', len(asyncio.Task.all_tasks()))
    print('Active tasks count: ', len(
        [task for task in asyncio.Task.all_tasks() if not task.done()])
    )

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

哪些输出：

Tasks count:  1
Tasks count:  2
Tasks count:  3
Tasks count:  4
Tasks count:  4
Active tasks count:  1

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