From: "k0kubun (Takashi Kokubun) via ruby-core" <ruby-core@...>
Date: 2026-01-13T01:15:11+00:00
Subject: [ruby-core:124493] [Ruby Bug#21812] Kernel#sleep without arguments returns immediately when subprocess exits in another thread (regression in Ruby 4.0)

Issue #21812 has been updated by k0kubun (Takashi Kokubun).

Backport changed from 3.2: DONTNEED, 3.3: DONTNEED, 3.4: DONTNEED, 4.0: REQUIRED to 3.2: DONTNEED, 3.3: DONTNEED, 3.4: DONTNEED, 4.0: DONE

ruby_4_0 commit:ac596948d4008c6e117449786c62de4e45e434bf merged revision(s) commit:7e81bf5c0c8f43602e6d901f4253dca2f3d71745.

----------------------------------------
Bug #21812: Kernel#sleep without arguments returns immediately when subprocess exits in another thread (regression in Ruby 4.0)
https://bugs.ruby-lang.org/issues/21812#change-116045

* Author: jaimevelaz (Jaime Velaz)
* Status: Closed
* Assignee: luke-gru (Luke Gruber)
* ruby -v: ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [arm64-darwin25]
* Backport: 3.2: DONTNEED, 3.3: DONTNEED, 3.4: DONTNEED, 4.0: DONE
----------------------------------------
**Description**

In Ruby 4.0.0, Kernel#sleep without arguments returns 0 immediately when a subprocess (spawned via backticks in another thread) exits. This is a regression from Ruby 3.4.8 where sleep blocks indefinitely as expected.

Note: sleep(N) with an argument is not affected.

---
**Steps to reproduce**

```
# test_sleep.rb
Thread.new do
  sleep 0.3
  `echo hello`  # Spawns subprocess
  puts "Subprocess exited"
end

puts "Main thread sleeping..."
result = sleep  # Should block forever
puts "sleep returned: #{result.inspect}"
```

Run with:
`$ ruby test_sleep.rb`

---
Actual result (Ruby 4.0.0):

Main thread sleeping...
Subprocess exited
sleep returned: 0

The program exits immediately after the subprocess completes.

---
Expected result (Ruby 3.4.8 behavior):

Main thread sleeping...
Subprocess exited
(process blocks indefinitely until interrupted by signal)

The program should block forever until explicitly interrupted by SIGINT/SIGTERM.




-- 
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