Bug #16277

UNIXServer#listen fails with Errno::EADDRINUSE error under Windows 10 / WSL Ubuntu 18.04

Added by bradland (Brad Landers) 9 months ago. Updated 9 months ago.

Target version:
ruby -v:
ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux-gnu]


When running the following script under Windows 10 / WSL Ubuntu 18.04, an Errno::EADDRINUSE error is thrown. Expected result is that the script would run and simply exit.

#!/usr/bin/env ruby

# This script establishes a UNIX server socket.
# Expected result: Script should run and immediately exit.
# Actual result: Script fails with Errno::EADDRINUSE error.
# Environment: Windows 10 Pro, WSL, Ubuntu 18.04.2, ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux-gnu]
# To reproduce: Create a tmp folder, copy this script there, and execute.

require 'socket'

path = File.expand_path('listen.sock')
backlog = 5

s =
if backlog
  s.listen backlog

File.delete(path) if File.exists?(path)

The bug was discoverd as part of Puma (gem) issue #1521:

Updated by shyouhei (Shyouhei Urabe) 9 months ago

This is very nuanced. I'm not sure who is in charge of the exception.'s return value socket is already listened inside of the method. Calling listen again on a socket that is already listening, might or might not error depending on OS. That's why you see exceptions on WSL and not on Linux.

The problem I see is why at the beginning you want to listen again a socket returned from I guess you want to change (maybe increase) the backlog? Then there seems to be no way for to change backlog than listening again. Is it possible for a WSL-hosted application to dynamically change the backlog per-socket? If not (== there is no way but to specify enough backlog at the birth), I guess this is a misfeature of UNIXServer.

Updated by MSP-Greg (Greg L) 9 months ago

Would something like the following yield an equivalent object?

require 'socket'
sock = :UNIX, :STREAM
sock.bind Addrinfo.unix('tmp.sock', :STREAM)
sock.listen 1024
puts sock.local_address.unix?

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