From: "jhawthorn (John Hawthorn) via ruby-core" <ruby-core@...>
Date: 2025-08-21T19:37:59+00:00
Subject: [ruby-core:123034] [Ruby Bug#19407] 2 threads taking from current ractor will hang forever

Issue #19407 has been updated by jhawthorn (John Hawthorn).

Status changed from Assigned to Closed

I believe the Ractor::Port interface doesn't suffer from this issue

```
ruby -e 'th = 2.times.map { |i| Thread.new { p(i => Ractor.receive) } }; %w[hello world].each { Ractor.current.send it }; th.each(&:join)'
{0 => "hello"}
{1 => "world"}
```

However I think it might make sense for us to forbid `Ractor.current.join`/`Ractor.current.value`

```
��� ruby -e 'Thread.current.join'
-e:1:in 'Thread#join': Target thread must not be current thread (ThreadError)
        from -e:1:in '<main>'

��� ruby -e 'Ractor.current.join'
(nothing, but exits cleanly with Ctrl-C)
```

----------------------------------------
Bug #19407: 2 threads taking from current ractor will hang forever
https://bugs.ruby-lang.org/issues/19407#change-114345

* Author: luke-gru (Luke Gruber)
* Status: Closed
* Assignee: ractor
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
In the current implementation of Ractors, it's possible to `take` from the current ractor. This could be useful
when co-ordinating threads:

```ruby
t = Thread.new do
  obj = Ractor.current.take
  p obj # do some work with obj
end
t0 = Thread.new do
  obj = Ractor.current.take
  p obj # do some work with obj
end
Ractor.yield :go
```

However it hangs forever:

```ruby
t = Thread.new do
  obj = Ractor.current.take
  p obj
end
t0 = Thread.new do
  obj = Ractor.current.take
  p obj
end
sleep 0.5
```

Should "self-take" be disabled, or was it designed to allow it but this is just a bug?



-- 
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