python - 异步客户端 : `connection_lost` not called, 导致 ResourceWarning

Question

我正在使用 asyncio 客户端连接服务器，然后断开连接。

• 如果我连接到同一台计算机上的服务器程序，连接正常关闭。 添加:当我开始向连接写入数据时，此连接也开始提供警告有时。请参阅下面的第二个代码版本。

• 如果我连接到本地网络上的设备，我会收到未封闭传输的ResourceWarning。

如何正确关闭连接？

我在 Windows 7(64 位)上使用 Python 3.6.0(32 位)。

第一次尝试

相关代码:

import asyncio
import logging
import warnings

class ClientConnection(asyncio.Protocol):
    def connection_made(self, transport):
        self.transport = transport
        transport.write_eof()  # Send EOF to close connection

    def connection_lost(self, exception):
        self.transport.close()
        super().connection_lost(exception)

def main():
    logging.basicConfig(level=logging.DEBUG)
    eventLoop = asyncio.get_event_loop()
    eventLoop.set_debug(True)
    warnings.simplefilter('always', ResourceWarning)  # enables ResourceWarning
    #co = eventLoop.create_connection(ClientConnection, '127.0.0.1', 7001)     # Works without warning
    co = eventLoop.create_connection(ClientConnection, '192.168.10.66', 7001)  # Gives warning
    try:
        eventLoop.run_until_complete(co)
    finally:
        eventLoop.close()

if __name__ == "__main__":
    main()

控制台输出:

DEBUG:asyncio:Using selector: SelectSelector
DEBUG:asyncio:connect <socket.socket fd=240, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6> to ('19
2.168.10.66', 7001)
DEBUG:asyncio:poll took 0.000 ms: 1 events
DEBUG:asyncio:<socket.socket fd=240, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('192.168
.10.62', 64587), raddr=('192.168.10.66', 7001)> connected to 192.168.10.66:7001: (<_SelectorSocketTransport fd=240 read=
polling write=<idle, bufsize=0>>, <__main__.ClientConnection object at 0x005EBD90>)
DEBUG:asyncio:Close <_WindowsSelectorEventLoop running=False closed=False debug=True>
sys:1: ResourceWarning: unclosed <socket.socket fd=240, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto
=6, laddr=('192.168.10.62', 64587), raddr=('192.168.10.66', 7001)>
C:\Program Files (x86)\Python36-32\lib\asyncio\selector_events.py:631: ResourceWarning: unclosed transport <_SelectorSoc
ketTransport fd=240>
  source=self)

第二次尝试

我对代码进行了以下更改:

• 从 connection_lost 中移除了 transport.close()
• 向连接写入一些数据
• 添加了 data_received 和 eof_received 回调
• 添加了更多调试日志

观察:

• 我尝试将 transport.close() 添加到 connection_made，但它总是会导致 OSError: [WinError 10038]。 注意:这可能是另一个问题，所以让我们暂时忽略它，假设我不会这样做。
• 当向套接字写入一些数据时，本地主机连接也开始发出警告，但并非总是如此。
• 当它发出警告时，connection_lost 不会被调用。为什么？

修改后的代码:

import asyncio
import logging
import warnings

class ClientConnection(asyncio.Protocol):
    def connection_made(self, transport):
        logging.debug('connection_made')
        self.transport = transport
        transport.write(b'1234\r')
        transport.write_eof()  # Send EOF to close connection
        #transport.close()  # Cannot close here either, gives 'OSError: [WinError 10038]'

    def connection_lost(self, exception):
        logging.debug('connection_lost')
        super().connection_lost(exception)

    def data_received(self, data):
        logging.debug('received {} bytes'.format(len(data)))

    def eof_received(self):
        logging.debug('EOF received')
        self.transport.close()

def main():
    logging.basicConfig(level=logging.DEBUG)
    eventLoop = asyncio.get_event_loop()
    eventLoop.set_debug(True)
    warnings.simplefilter('always', ResourceWarning)  # enables ResourceWarning
    #co = eventLoop.create_connection(ClientConnection, '127.0.0.1', 7001)     # Works without warning
    co = eventLoop.create_connection(ClientConnection, '192.168.10.66', 7001)  # Gives warning
    try:
        eventLoop.run_until_complete(co)
        logging.debug('done')
    finally:
        eventLoop.close()

if __name__ == "__main__":
    main()

成功时的输出:

...
DEBUG:root:EOF received
DEBUG:root:connection_lost
DEBUG:root:done
DEBUG:asyncio:Close <_WindowsSelectorEventLoop running=False closed=False debug=True>

失败时的输出(注意缺少connection_lost):

...
DEBUG:root:EOF received
DEBUG:root:done
DEBUG:asyncio:Close <_WindowsSelectorEventLoop running=False closed=False debug=True>
sys:1: ResourceWarning: unclosed <socket.socket fd=240, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto
=6, laddr=('127.0.0.1', 63858), raddr=('127.0.0.1', 7001)>
C:\Program Files (x86)\Python36-32\lib\asyncio\selector_events.py:631: ResourceWarning: unclosed transport <_SelectorSoc
ketTransport closing fd=240>
  source=self)

Answer 1

要么等待服务器关闭您的连接，要么使用 transport.close() 关闭传输。这也会触发 connection_lost(不要从 connection_lost 调用 transport.close()!):

class ClientConnection(asyncio.Protocol):
    def connection_made(self, transport):
        logging.debug("connection made, calling write eof")
        transport.write_eof()
        logging.debug("after calling write eof, calling close")
        transport.close()
        logging.debug("after calling close")

    def connection_lost(self, exception):
        logging.debug("connection lost")
        super().connection_lost(exception)

如果您多尝试一些，您可能还会为您的本地计算机收到一些 ResourceWarning。例如，尝试在 write_eof() 之前添加 transport.write(b'hello world!') 或使本地服务器响应速度变慢。