Deadlock regression using Edge Futures chain & zip

[ms-ati]

This appears to be a regression of #611

To reproduce:

gem install concurrent-ruby-edge -v 0.3.0
irb -rconcurrent-edge

Array.new(4) do 
  Concurrent::Promises.zip_futures(
    *Array.new(5) do |i|
      Concurrent::Promises.delay do 
        puts "starting #{i}"
        sleep(i)
        puts "done #{i}"
        i
      end
    end
  )
end.inject { |a, b| a.then { b }.flat }.value!

I see this output:

starting 4
starting 3
starting 2
starting 0
done 0
starting 1
done 1
done 2
done 3
done 4
fatal: No live threads left. Deadlock?
	from /Users/marcsiegel/.gem/ruby/2.3.1/gems/concurrent-ruby-edge-0.3.0/lib/concurrent/edge/promises.rb:756:in `sleep'
	from /Users/marcsiegel/.gem/ruby/2.3.1/gems/concurrent-ruby-edge-0.3.0/lib/concurrent/edge/promises.rb:756:in `wait'
	from /Users/marcsiegel/.gem/ruby/2.3.1/gems/concurrent-ruby-edge-0.3.0/lib/concurrent/edge/promises.rb:756:in `block in wait_until_resolved'
	from /Users/marcsiegel/.gem/ruby/2.3.1/gems/concurrent-ruby-edge-0.3.0/lib/concurrent/edge/promises.rb:752:in `synchronize'
	from /Users/marcsiegel/.gem/ruby/2.3.1/gems/concurrent-ruby-edge-0.3.0/lib/concurrent/edge/promises.rb:752:in `wait_until_resolved'
	from /Users/marcsiegel/.gem/ruby/2.3.1/gems/concurrent-ruby-edge-0.3.0/lib/concurrent/edge/promises.rb:1177:in `wait_until_resolved!'
	from /Users/marcsiegel/.gem/ruby/2.3.1/gems/concurrent-ruby-edge-0.3.0/lib/concurrent/edge/promises.rb:951:in `value!'
	from (irb):12
	from /Users/marcsiegel/.rubies/ruby-2.3.1/bin/irb:11:in `<main>'

---

• Operating system: mac
• concurrent-ruby version: 1.0.4
• concurrent-ruby-ext installed: no
• concurrent-ruby-edge used: yes (0.3.0)

[pitr-ch]

Thanks! Indeed there is another problem. I'll have a look. Smaller reproducer:

Array.new(3) do |i| # works for 2
  Concurrent::Promises.delay do
    puts "starting #{i}"
    sleep(i)
    puts "done #{i}"
    i
  end
end.inject { |a, b| a.then { b }.flat }.value!

It probably does not correctly combine delayed collections.

[pitr-ch]

will be fixed with #625 and in a next release.