RuntimeError：传输使用文件描述符 8答案

【问题标题】：RuntimeError: File descriptor 8 is used by transportRuntimeError：传输使用文件描述符 8
【发布时间】：2019-07-25 11:30:45
【问题描述】：

最小的演示示例：

import asyncio

async def main():
    c1_reader, c1_writer = await asyncio.open_connection(host='google.com', port=80)
    c1_socket = c1_writer.get_extra_info('socket')
    c1_socket.close()

    c2_reader, c2_writer = await asyncio.open_connection(host='google.com', port=80)

asyncio.run(main())

运行这个程序会报这个错误：

$ python3 asyncio_fd_used.py
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/selector_events.py", line 469, in _sock_connect
    sock.connect(address)
BlockingIOError: [Errno 36] Operation now in progress

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "asyncio_fd_used.py", line 11, in <module>
    asyncio.run(main())
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/runners.py", line 43, in run
    return loop.run_until_complete(main)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/base_events.py", line 579, in run_until_complete
    return future.result()
  File "asyncio_fd_used.py", line 9, in main
    c2_reader, c2_writer = await asyncio.open_connection(host='google.com', port=80)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/streams.py", line 77, in open_connection
    lambda: protocol, host, port, **kwds)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/base_events.py", line 941, in create_connection
    await self.sock_connect(sock, address)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/selector_events.py", line 463, in sock_connect
    self._sock_connect(fut, sock, address)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/selector_events.py", line 477, in _sock_connect
    self.add_writer(fd, self._sock_connect_cb, fut, sock, address)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/selector_events.py", line 333, in add_writer
    self._ensure_fd_no_transport(fd)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/asyncio/selector_events.py", line 244, in _ensure_fd_no_transport
    f'File descriptor {fd!r} is used by transport '
RuntimeError: File descriptor 8 is used by transport <_SelectorSocketTransport fd=8 read=polling write=<idle, bufsize=0>>

只是为了解释为什么我在做低级别的socket.close() 而不是异步级别的writer.close()：我正在尝试一些代码来发送 RST 数据包。但我可以想象人们会打电话给socket.close() 的其他原因，甚至可能是无意的。

【问题讨论】：

标签： python python-3.x network-programming python-asyncio

【解决方案1】：

问题是低级套接字已关闭，但 asyncio 不知道这一点并认为它仍然是打开的。出于某种原因（性能？）asyncio 记住了套接字文件描述符（fileno）。

当一个新连接打开时，操作系统给它相同的文件描述符编号，并且 asyncio 开始恐慌，因为它具有与之前的连接相关联的完全相同的 fd 编号。

解决方案：告诉 asyncio 套接字已关闭 :)

import asyncio

async def main():
    c1_reader, c1_writer = await asyncio.open_connection(host='google.com', port=80)
    c1_socket = c1_writer.get_extra_info('socket')
    c1_socket.close()
    c1_writer.close()  # <<< here

    c2_reader, c2_writer = await asyncio.open_connection(host='google.com', port=80)

asyncio.run(main())

此代码运行时不会引发错误。

【讨论】：