python-3.x - 计算事件循环中的事件任务

Question

我如何找出事件循环中有多少事件任务？
在文档中，我仅找到asyncio.Task.all_tasks()，但是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。您可以简单地通过done()过滤任务以获取事件任务:

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