From: "Eregon (Benoit Daloze)" <noreply@...>
Date: 2022-09-27T17:00:04+00:00
Subject: [ruby-core:110109] [Ruby master Bug#19020] Unexpected timeout thread appears in ThreadGroup

Issue #19020 has been updated by Eregon (Benoit Daloze).

Status changed from Open to Closed

Fixed in https://github.com/ruby/timeout/pull/22

----------------------------------------
Bug #19020: Unexpected timeout thread appears in ThreadGroup
https://bugs.ruby-lang.org/issues/19020#change-99367

* Author: larskanis (Lars Kanis)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-09-23T20:17:54Z master 912ea8257a) [x86_64-linux]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
The new timeout implementation creates a thread at the very first use.
This has the side effect, that this management thread appears in a surrounding `ThreadGroup`.
See this example:

```ruby
require "timeout"

threadgroup = ThreadGroup.new
thr = Thread.new do
  Timeout.timeout(10){}
end
threadgroup.add(thr)
p after_add: threadgroup, list: threadgroup.list

sleep 0.2
p after_sleep: threadgroup, list: threadgroup.list
```

On ruby master branch the ThreadGroup lists this common management thread of the timeout library:

```ruby
$ ruby test-threadgroup.rb
{:after_add=>#<ThreadGroup:0x00007f12f120adb8>, :list=>[#<Thread:0x00007f12f120acc8 test-threadgroup.rb:4 run>]}
{:after_sleep=>#<ThreadGroup:0x00007f12f120adb8>, :list=>[#<Thread:0x00007f12f120a1d8@Timeout stdlib thread /home/lars/.rvm/rubies/ruby-head/lib/ruby/3.2.0+2/timeout.rb:101 sleep_forever>]}
```

While older ruby versions don't show any timeout thread:
```ruby
$ ruby test-threadgroup.rb
{:after_add=>#<ThreadGroup:0x0000556315b26b50>, :list=>[#<Thread:0x0000556315b26b28@test-threadgroup.rb:4 run>]}
{:after_sleep=>#<ThreadGroup:0x0000556315b26b50>, :list=>[]}
```




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