Bug #19020: Unexpected timeout thread appears in ThreadGroup

• Status: Closed
• Assignee: -
• Target version: -
• 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

[larskanis (Lars Kanis)]

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:

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 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 test-threadgroup.rb
{:after_add=>#<ThreadGroup:0x0000556315b26b50>, :list=>[#<Thread:[e-mail]:4 run>]}
{:after_sleep=>#<ThreadGroup:0x0000556315b26b50>, :list=>[]}

[larskanis (Lars Kanis)]

A fix is here: https://github.com/ruby/timeout/pull/22

[Eregon (Benoit Daloze)]

• Status changed from Open to Closed

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

[mame (Yusuke Endoh)]

• Related to Feature #19440: Deprecate ThreadGroup added