计算事件循环中的活动任务

Question

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()但它是简单的增量计数器:

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

预期产量:

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

Answer 1

all_tasks返回所有已注册的任务,包括已完成的任务.您可以简单地过滤任务done()以获取活动的任务:

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())

哪个输出:

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

Answer 2

在 Python 3.7+ 中，有一个asyncio.all_tasks()方法可以返回当前运行循环的未完成任务。

所以这简化为：

count_active_tasks = len(asyncio.all_tasks())