TimerSet's priority queue has nil elements

[gmalkas]

Hey,

it seems TimerSet's priority queue has some nil elements:

NoMethodError: undefined method `time' for nil:NilClass
    /.bundle/jruby/1.9/bundler/gems/concurrent-ruby-48c74dee7152/lib/concurrent/executor/timer_set.rb:108 :in `<=>`
    /.bundle/jruby/1.9/bundler/gems/concurrent-ruby-48c74dee7152/lib/concurrent/collection/priority_queue.rb:276 :in `pop`
    /.bundle/jruby/1.9/bundler/gems/concurrent-ruby-48c74dee7152/lib/concurrent/executor/timer_set.rb:139 :in `process_tasks`
    /.bundle/jruby/1.9/bundler/gems/concurrent-ruby-48c74dee7152/lib/concurrent/executor/timer_set.rb:131 :in `process_tasks`

Here is the state of variables when the exception was raised:

    {
      "self" => "#<struct Concurrent::TimerSet::Task time=1416912118.263, args=[#<Concurrent::Event:0x59a176fc @mutex=#<Mutex:0x38684d54>, @condition=#<Concurrent::Condition:0x47ace2ba @condition=#<ConditionVariable:0x27594619>>, @set=false>], op=#<Proc:0x5609277d@/.bundle/jruby/1.9/bundler/gems/concurrent-ruby-48c74dee7152/lib/concurrent/timer_task.rb:318 (lambda)>>",
      "other" => "nil"
    }

This seems a bit strange to me, as reading through TimerSet code I do not see how a nil element could be pushed onto the queue.

Any idea?

Version information:
concurrent-ruby 0.7.0
jruby 1.7.16.1 on Java 8

Thanks!

[jdantonio]

Thanks for letting us know. And thank you for providing so my detail! Off the top of my head I can't think of what the problem may be, but it's definitely a problem. I wrote all that code so I'll take a look at it this weekend.

[gmalkas]

Thanks for the information. Let me know if you need more context to debug this :)

[pitr-ch]

Thanks @gmalkas.
@jdantonio It may be fixed in 296a567.

[jdantonio]

@gmalkas Can you please try running your tests against the latest master branch? The fix @pitr-ch references looks like it may have fixed the issue.

[gmalkas]

@jdantonio unfortunately, this exception was taken from a production system. I do not have a prepared test to check this error in particular, since it was fairly unpredictable (which makes sense since according to the fix, it was some kind of race-condition error due to missing synchronize).

For now, we are using Java Timers as a replacement, but we will try your fix as soon as it is available as a gem release and let you know if we see this error again.

Thanks!

[pitr-ch]

Thanks.

[jdantonio]

@gmalkas How soon do you need an update? I was planning to release 0.7.1 prior to RubyConf but wasn't able to. The plan right now is to wait a couple of weeks, but we could create a release immediately if you need us to.

[jdantonio]

0.7.1 has been released.

[jdantonio]

@gmalkas If you have an opportunity to field test 0.7.1 we would greatly appreciate your effort and your feedback.

[obrok]

I'm currently working on upgrading to 0.7.1 in the project we're doing with @gmalkas. Needs a bit of work because we were using ImmediateExecutor with Actors for specs, and that all needs to go now :)