Fix deadlock of Future when the handler raises Exception

[amutake]

I found deadlock situation in using Future when the handler raises Exception (not StandardError).

require 'concurrent'

future = Concurrent::Future.new do
  raise Exception
end
future.execute
future.value #=> deadlock

/Users/shohei-yasutake/work/concurrent-ruby/lib/concurrent/atomic/condition.rb:50:in `sleep': No live threads left. Deadlock? (fatal)
    from /Users/shohei-yasutake/work/concurrent-ruby/lib/concurrent/atomic/condition.rb:50:in `wait'
    from /Users/shohei-yasutake/work/concurrent-ruby/lib/concurrent/atomic/condition.rb:50:in `wait'
    from /Users/shohei-yasutake/work/concurrent-ruby/lib/concurrent/atomic/event.rb:89:in `wait'
    from /Users/shohei-yasutake/work/concurrent-ruby/lib/concurrent/obligation.rb:80:in `wait'
    from /Users/shohei-yasutake/work/concurrent-ruby/lib/concurrent/obligation.rb:71:in `value'
    from example.rb:7:in `<main>'

It is because the exception raised in SafeTaskExecutor.new(@task).execute(*@args) is not caught and complete(success, val, reason) is not called.

https://github.com/ruby-concurrency/concurrent-ruby/blob/master/lib/concurrent/future.rb#L85-L86

So I fixed to catch Exception in SafeTaskExecutor.

[pitr-ch]

Thanks for reporting and for the fix!

[pitr-ch]

Could you also test that future.reason is set to the Exception instance?

[amutake]

Thank you for quick response!

I added a test case. Could you check it?

[jdantonio]

@amutake Thank you very much for catching this and taking the time to fix it! I'll take a look at this in more detail this evening. Hopefully we can get it merged today.