为什么它说从未等待过FETCH函数? [英] Why it says fetch function was never awaited?
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问题描述
我正在尝试执行asynchronous requests
,如下所示:
# Example 2: asynchronous requests
import asyncio
import aiohttp
import time
import concurrent.futures
no = int(input("time of per "))
num_requests = int(input("enter the no of threads "))
no_1 = no
avg = 0
async def fetch():
async with aiohttp.ClientSession() as session:
await session.get('http://google.com')
while no > 0:
start = time.time()
async def main():
with concurrent.futures.ThreadPoolExecutor(max_workers=num_requests) as executor:
loop = asyncio.get_event_loop()
futures = [
loop.run_in_executor(
executor,
fetch
)
for i in range(num_requests)
]
for response in await asyncio.gather(*futures):
pass
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
temp = (time.time()-start)
print(temp)
avg = avg + temp
no = no - 1
print("Average is ",avg/no_1)
我收到错误
RuntimeWarning: coroutine 'fetch' was never awaited
handle = None # Needed to break cycles when an exception occurs
即使我在fetch
函数中使用await
。为什么会这样?
推荐答案
fetch
包含ANawait
,但没有人在等待fetch()
本身。相反,它是由run_in_executor
调用的,run_in_executor
是为同步函数设计的。虽然您当然可以调用与同步函数类似的异步函数,但除非由协程程序等待或提交给事件循环,否则它不会产生任何效果,而问题中的代码既不执行这两种操作,也不执行这两项操作。
fetch()
这样的协同例程,请使用create_task()
将它们提交到运行循环,并使用gather
等待它们en mass(您几乎已经在这样做了)。例如:
async def main():
loop = asyncio.get_event_loop()
tasks = [loop.create_task(fetch())
for i in range(num_requests)]
for response in await asyncio.gather(*tasks):
pass # do something with response
main()
可以按照问题:
loop = asyncio.get_event_loop()
while no > 0:
start = time.time()
loop.run_until_complete(main())
...
no = no - 1
但是,如果也为计时代码创建一个协程,并且只调用loop.run_until_complete()
一次:
async def avg_time():
while no > 0:
start = time.time()
await main()
...
no = no - 1
loop = asyncio.get_event_loop()
loop.run_until_complete(avg_time())
最后,您可能希望在main
或everything
中创建ClientSession
,并将相同的会话对象传递给每个fetch
调用。会话通常在多个请求之间共享,不会为每个单独的请求重新创建。
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