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如何管理单个aiohttp.ClientSession?

aiohttp python-asyncio python

Tamás Szelei · 技术社区 · 6 年前

import aiohttp
import asyncio

async def fetch(session, url):
  async with session.get(url) as response:
    return await response.text()

async def main(url, session):
  print(f"Starting '{url}'")
  html = await fetch(session, url)
  print(f"'{url}' done")

urls = (
  "https://python.org",
  "https://twitter.com",
  "https://tumblr.com",
  "https://example.com",
  "https://github.com",
)

loop = asyncio.get_event_loop()
session = aiohttp.ClientSession()
loop.run_until_complete(asyncio.gather(
  *(loop.create_task(main(url, session)) for url in urls)
))
# session.close()   <- this doesn't make a difference

但是,在协同程序之外创建ClientSession显然不是一条路:

â python 1_async.py
1_async.py:30: UserWarning: Creating a client session outside of coroutine is a very dangerous idea
  session = aiohttp.ClientSession()
Creating a client session outside of coroutine
client_session: 
Starting 'https://python.org'
Starting 'https://twitter.com'
Starting 'https://tumblr.com'
Starting 'https://example.com'
Starting 'https://github.com'
'https://twitter.com' done
'https://example.com' done
'https://github.com' done
'https://python.org' done
'https://tumblr.com' done
1_async.py:34: RuntimeWarning: coroutine 'ClientSession.close' was never awaited
  session.close()
Unclosed client session
client_session: 
Unclosed connector
connections: ['[(, 15024.110107067)]', '[(, 15024.147785039)]', '[(, 15024.252375415)]', '[(, 15024.292646968)]', '[(, 15024.342368087)]', '[(, 15024.466971983)]', '[(, 15024.602057745)]', '[(, 15024.837045568)]']
connector:

FWIW,这是 main

async def main(url):
  async with aiohttp.ClientSession() as session:
    print(f"Starting '{url}'")
    html = await fetch(session, url)
    print(f"'{url}' done")

正确的方法是什么?我考虑过将一个url列表传递给main,但无法使其以非顺序方式工作。

1 回复 | 直到 6 年前

Sraw 6 年前

Creating a client session outside of coroutine is a very dangerous idea 因为当您创建它时,它被绑定到当前循环。如果你在之后改变跑步循环,它将挂起。但如果你足够小心地使用它,你可以忽略它。 Related doc .

至于我,我只是忽略了这个警告。但也很容易克服:

async def create_session():
    return aiohttp.ClientSession()

session = asyncio.get_event_loop().run_until_complete(create_session())

此外,您不需要显式地创建 Task 对象,但只执行此协程函数:

loop.run_until_complete(asyncio.gather(
  *(main(url, session) for url in urls)
))

最后,别忘了 close 是一次联程旅行。你应该用 loop.run_until_complete(session.close()) 结束 session .

顺便说一句,如果您想创建一个类似异步的循环,可以参考 my another answer