使用 asyncio 构建一组任务，但总时间比最长任务花费的时间长答案

【问题标题】：Building a set of tasks with asyncio, but total time takes longer than longest task使用 asyncio 构建一组任务，但总时间比最长任务花费的时间长
【发布时间】：2022-11-02 01:59:02
【问题描述】：

在以下代码中，当我使用 asyncio 时，为什么需要 10(0+1+2+3+4) 秒而不是 4 秒才能完成？

import asyncio,time

async def say_after(delay, what):
    await asyncio.sleep(delay)
    print(f"what = {what}, at {time.strftime('%X')}")


background_tasks = set()

async def main():
    for i in range(5):
        task = asyncio.create_task(say_after(delay=i,what=i))
        
        # Add task to the set. This creates a strong reference.
        background_tasks.add(task)
        
        await task
        
        # To prevent keeping references to finished tasks forever,
        # make each task remove its own reference from the set after
        # completion:
        task.add_done_callback(background_tasks.discard) # discard is a set method.
        
if __name__=="__main__":
    asyncio.run(main())

结果在图片中。

【问题讨论】：

标签： python python-asyncio

【解决方案1】：

在循环外执行任务

import asyncio,time

async def say_after(delay, what):
    await asyncio.sleep(delay)
    print(f"what = {what}, at {time.strftime('%X')}")


background_tasks = set()

async def main():
    for i in range(5):
        task = asyncio.create_task(say_after(delay=i,what=i))
        
        # Add task to the set. This creates a strong reference.
        background_tasks.add(task)
        
    await task
    
    # To prevent keeping references to finished tasks forever,
    # make each task remove its own reference from the set after
    # completion:
    task.add_done_callback(background_tasks.discard) # discard is a set method.
        
if __name__=="__main__":
    asyncio.run(main())

【讨论】：