[ruby-core:123817] [Ruby Bug#20907] Fiber scheduler does not correctly re-lock mutex if `Mutex#sleep` is interrupted.

16 Nov 2025


      Issue #20907 has been updated by ioquatix (Samuel Williams).


Cross referencing: https://github.com/socketry/async/issues/424

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Bug #20907: Fiber scheduler does not correctly re-lock mutex if `Mutex#sleep` is interrupted.
https://bugs.ruby-lang.org/issues/20907#change-115220

* Author: ioquatix (Samuel Williams)
* Status: Closed
* Assignee: ioquatix (Samuel Williams)
* Backport: 3.1: REQUIRED, 3.2: DONE, 3.3: DONE
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The following test fails with a `ThreadError` instead of a `RuntimeError`:

```ruby
  def test_condition_variable
    condition_variable = ::Thread::ConditionVariable.new
    mutex = ::Thread::Mutex.new

    error = nil

    thread = Thread.new do
      Thread.current.report_on_exception = false

      scheduler = Scheduler.new
      Fiber.set_scheduler scheduler

      fiber = Fiber.schedule do
        begin
          mutex.synchronize do
            condition_variable.wait(mutex)
          end
        rescue => error
        end
      end

      fiber.raise(RuntimeError)
    end

    thread.join
    assert_kind_of RuntimeError, error
  end
```

Fix: https://github.com/ruby/ruby/pull/12158


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