[ruby-core:120705] [Ruby master Bug#21037] Ractors hang with multiple threads

15 Jan 2025

      Issue #21037 has been updated by luke-gru (Luke Gruber).

It seems calling `ractor.take` from multiple threads is unsupported at the moment. I don't know if this is a limitation or a bug. Of course, you can work around it and call `select` or `take` from a single thread, like main, and signal a ready event with a queue or something for the consumer threads.

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Bug #21037: Ractors hang with multiple threads
https://bugs.ruby-lang.org/issues/21037#change-111539

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* ruby -v: ruby 3.5.0dev (2025-01-14T20:59:39Z master f1e32914eb) +PRISM [x86_64-linux]
* Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
The following program hangs, but I don't expect it to hang:

```ruby
# frozen_string_literal: true

class Map
  def initialize
    @r = Ractor.new {
      cache = { "int" => "integer", "bool" => "boolean" }
      loop do
        key = receive
        Ractor.yield key
      end
    }
    freeze
  end

  def fetch(key)
    @r.send key
    m = @r.take
    raise unless key == m
    m
  end
end

tm = Map.new
t1 = Thread.new { 10.times { |i| p [i + 1,tm.fetch("int")] } }
t2 = Thread.new { 10.times { |i| p [i + 1, tm.fetch("bool")] } }

t1.join
t2.join
```

I'm not sure why this program hangs yet, but it does both on macOS and Linux. I've tested with master, Ruby 3.4, and Ruby 3.3.  I'm not sure why it's hanging yet, but I wanted to file an issue.

-- 
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