From: "byroot (Jean Boussier)" <noreply@...>
Date: 2022-11-05T18:00:15+00:00
Subject: [ruby-core:110626] [Ruby master Bug#19105] mutex: Raise a ThreadError when detecting a fiber deadlock

Issue #19105 has been reported by byroot (Jean Boussier).

----------------------------------------
Bug #19105: mutex: Raise a ThreadError when detecting a fiber deadlock
https://bugs.ruby-lang.org/issues/19105

* Author: byroot (Jean Boussier)
* Status: Open
* Priority: Normal
* Backport: 2.7: DONTNEED, 3.0: REQUIRED, 3.1: REQUIRED
----------------------------------------
The following code can lead to a deadlock but not raise any error:

```ruby
mutex = Mutex.new
mutex.synchronize do
  error = assert_raise ThreadError do
    Fiber.new do
      mutex.lock
    end.resume
  end
end
```

If no fiber scheduler is registered, and both the fiber that currently own the lock and the one trying to acquire it belongs to the same thread, then this deadlock situation cannot possibly resolve (aside from a signal interrupt maybe).

Discussed in https://bugs.ruby-lang.org/issues/17827#note-10
Pull request: https://github.com/ruby/ruby/pull/6680




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