Issue #16277 has been updated by shyouhei (Shyouhei Urabe).


This is very nuanced.  I'm not sure who is in charge of the exception.

`UNIXServer.new`'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 `UNIXServer.new`.  I guess you want to change (maybe increase) the backlog?  Then there seems to be no way for `UNIXServer.new` 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.

----------------------------------------
Bug #16277: UNIXServer#listen fails with Errno::EADDRINUSE error under Windows 10 / WSL Ubuntu 18.04
https://bugs.ruby-lang.org/issues/16277#change-82295

* Author: bradland (Brad Landers)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-linux-gnu]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
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.

``` ruby
#!/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 = UNIXServer.new(path)
if backlog
  s.listen backlog
else
  s.listen
end

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

The bug was discoverd as part of Puma (gem) issue #1521: https://github.com/puma/puma/issues/1521.



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