Issue 41308: socket.connect() slow to time out on Windows

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This issue has been migrated to GitHub: https://github.com/python/cpython/issues/85480

classification

Title:	socket.connect() slow to time out on Windows
Type:	performance	Stage:	test needed
Components:	Windows	Versions:	Python 3.10

process

Status:	open	Resolution:
Dependencies:		Superseder:
Assigned To:		Nosy List:	paul.moore, steve.dower, tim.golden, zach.ware
Priority:	normal	Keywords:

Created on 2020-07-15 21:21 by steve.dower, last changed 2022-04-11 14:59 by admin.

Messages (1)
msg373725 - (view)	Author: Steve Dower (steve.dower) *	Date: 2020-07-15 21:21
When connecting to localhost, socket.connect() takes two seconds on Windows (the default) to time out, but on Linux (including WSL) it times out immediately. Test code (assuming port 9999 has no listener): >>> import socket >>> socket.socket().connect(('localhost', 9999)) For a remote host, the timeout is approx 10s on Windows and 20s on WSL (I didn't test on a native Linux box). I'm told the correct fix is to specify TCP_INITIAL_RTO_NO_SYN_RETRANSMISSIONS [1] when connecting to localhost.

msg373725 - (view)

Author: Steve Dower (steve.dower) * (Python committer)

Date: 2020-07-15 21:21

When connecting to localhost, socket.connect() takes two seconds on Windows (the default) to time out, but on Linux (including WSL) it times out immediately.

Test code (assuming port 9999 has no listener):
>>> import socket
>>> socket.socket().connect(('localhost', 9999))

For a remote host, the timeout is approx 10s on Windows and 20s on WSL (I didn't test on a native Linux box).

I'm told the correct fix is to specify TCP_INITIAL_RTO_NO_SYN_RETRANSMISSIONS [1] when connecting to localhost.

History
Date	User	Action	Args
2022-04-11 14:59:33	admin	set	github: 85480
2020-07-15 21:21:16	steve.dower	create