Concurrency issues

[stugol]

I'm trying to use Rx in my Ruby project, but I'm having difficulty with concurrency. I have two threads, each pushing to its own observable. I am piping these two observables into a single Subject, and subscribing to that. However, the subscription is now being called in parallel, rather than having the messages queue up. I tried using a Scheduler, but they all appear to be broken:

   /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/scheduled_observer.rb:50:in `ensure_active': undefined method `schedule_recursive_with_state' for RX::CurrentThreadScheduler:Class (NoMethodError)

Incidentally, the concurrency issue doesn't seem to occur if I call Merge instead of piping them into a Subject.

How can I get help for this issue, please?

Cheers,
Stuart.

[ghost]

@stugol Can you present tests or snippets which reproduce the problem so that we could take a look?

[stugol]

After six months? Are you serious?

Maybe if you had responded within a sensible period of time, I would still have the code. As it stands however, I probably gave up on ever getting it resolved, and changed the code to work a different way.

I guess I could try to reproduce the problem from scratch. If I do this, are you going to respond quickly, or will it be another colossal waste of time?

[ghost]

Well, I was one of the watchers at that time. No active communications were made for a long time in the project. So I have decided to make it progress.

If you rewrite the code, I would appreciate it! If you don't, it's ok.

[mattpodwysocki]

@stugol that's my fault, not @minamimonji so please don't take it out on him. I am the maintainer of the project and I was lax in my work here as I was focused on RxJS and other libraries as my primary libraries and was hoping to get help to make this one a success.

[stugol]

Sure, no problem. I'll see what I can whip up.

[stugol]

Well, I've not had much time recently to attempt this, but I had a go this evening. I've not (yet) managed to reproduce the bug; primarily because all the other bugs keep getting in the way...

/var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/subjects/subject.rb:52:in `block in on_error': private method `check_disposed' called for #<RX::Subject:0x00000001b9e190> (NoMethodError)
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/subjects/subject.rb:51:in `synchronize'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/subjects/subject.rb:51:in `on_error'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/auto_detach_observer.rb:22:in `on_error_core'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/observer.rb:106:in `call'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/observer.rb:106:in `fail'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/observable.rb:76:in `rescue in schedule_subscribe'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/observable.rb:73:in `schedule_subscribe'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/concurrency/scheduled_item.rb:29:in `call'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/concurrency/scheduled_item.rb:29:in `invoke'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/concurrency/current_thread_scheduler.rb:67:in `run_trampoline'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/concurrency/current_thread_scheduler.rb:40:in `schedule_relative_with_state'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/concurrency/local_scheduler.rb:20:in `schedule_with_state'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/observable.rb:38:in `_subscribe'
        from /var/lib/gems/2.1.0/gems/Rx.rb-0.0.1/lib/rx/core/observable.rb:18:in `subscribe'

It would also help if [a] there was any documentation; and [b] the examples actually worked.

[stugol]

Alright, it would seem I was getting conflicts with previous versions of the library. It runs now. Although not correctly.

require "rx_ruby"
def produce_async_values
    RxRuby::Observable.create { |observer|
        Thread.new { loop { observer.on_next 1 } }
    }
end
subject = RxRuby::Subject.new
produce_async_values.subscribe subject
produce_async_values.subscribe subject
subject.subscribe_on_next { |n| puts n; sleep 0.2 }
sleep 2

This code should produce a stream of 1s, each on their own line. However, we seem to be getting race conditions, which shouldn't happen!

Actual output:

1
1
11

1
1
1
1
1
1
11

1
1
1
1
1
1
1
1

[stugol]

If I replace the two subscribe calls with produce_async_values.merge(produce_async_values).subscribe subject, the code works correctly.

However, these two techniques should produce identical output. If I pipe multiple streams into a subject, it should yield their values one at a time.

[ghost]

@stugol thank you!
We'll see what is happening on the code.

[ghost]

The on_next in the merge in surrounded by synchronize so that it prevents race conditions. However, the normal execution of the on_next in a subscription is not surrounded by synchronize. This causes race conditions.

@mattpodwysocki From the viewpoint of the Reactive Extensions, is this race condition expected? Or should we fix it?

[mattpodwysocki]

@minamimonji race conditions should not be expected at all so we're probably missing some mutex blocks

[ghost]

@stugol sorry for taking time to response. I made some changes to Subject to synchronize on_next, on_error, and on_complete. Can you give it a try? Here is the branch.
https://github.com/minamimonji/RxRuby/tree/fix_conccurency_issue

@mattpodwysocki Can you review it and make some comments?