aiohttp 并发请求被挂起

并发数 10，偶数请求立即完成，奇数请求被挂起超过 120 秒，是使用方法不对吗？

import asyncio
import aiohttp
import time

async def get(s, i):
    start = time.time()
    async with s.get('URL') as r:
        await r.read()
    print(i, ': {} s'.format(round(time.time() - start, 2)))


async def test():
    async with aiohttp.ClientSession() as s:
        await asyncio.gather(*[get(s, i) for i in range(10)])

if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(test())

结果

0 : 0.38 s
8 : 0.4 s
2 : 0.57 s
6 : 0.6 s
4 : 0.6 s
1 : 129.49 s
9 : 129.5 s
3 : 129.52 s
7 : 129.57 s
5 : 129.63 s