the two halves of my tasty brain

Events on a Train, Seeking a Ruby 1.9 World

So, true to my nature of nothing ever being quite “good enough” I’m already looking to add new features to OnStomp as well as making plans for what version 2.0 will look like.

Events on a separate loop

First, the new features, which is to say a new feature. One thing that’s been bothering me is that most events are dispatched from the IO thread of an OnStomp::Client instance. This means that long-running (or a long chain of short running) event handlers, once triggered, will have to finish running before further IO processing can occur. Another issue is that if an exception is raised in any of these callbacks, it will generally close the connection. In either case, IO can be negatively impacted by the programming approach the gem tries to encourage.

A second issue, slightly more subtle but just as significant, is that not all events are triggered in the same thread. The events that get triggered outside the IO processing thread are before_transmitting and before_<frame>. Let’s jump into an example:

main_thread = Thread.current

client = OnStomp.connect "stomp://localhost"

client.before_transmitting do |f, *_|
  # Thread.current == main_thread

client.before_send do |send_frame, *_|
  # Thread.current == main_thread

client.on_send do |send_frame, *_|
  # Thread.current != main_thread

client.after_transmitting do |f, *_|
  # Thread.current != main_thread
  # The current thread is the same here as in 'on_send'

client.send "/queue/test", "Hello World!"

Now, before_transmitting and before_send will be invoked (in that order) before the actual SEND frame is sent off to a dark and mysterious buffer where the IO processor will eventually get around to writing it to the socket. This means, you don’t have to worry about mutex locking and whatnot between these two groups of events. However, it still displeases me, as event handling will be split across two distinct threads.

So, to solve these issues I’m probably going to drop in a second thread. There are a few issues that need careful consideration. I’ll need to ensure that all before_* events are triggered before a client-generated frame gets sent to the IO write buffer. Also, it would be nice if all events triggered within the failover extension used the same thread as well by sharing an event dispatcher amongst all of the clients in the pool. This will keep the overall thread count down, and resolve some of its finer quirks that appear to be the result of events being triggered in a particular client’s IO processing thread.

In short, I’ll follow the lead of Arthur “Two Sheds” Jackson.

Welcome to the world of tomorrow!

I’m eagerly awaiting the day when JRuby has full Ruby 1.9.2 support, including non-blocking IO for OpenSSL connections. On that day, OnStomp 2.0 will hit the shelves, and it will require Ruby 1.9+. I have no intention of totally abandoning Ruby 1.8.7, and the OnStomp 1.0 branch will always support Ruby 1.8.7. That said, I am still looking forward to dropping all of the conditional code and strange shit like:

ENUMERATOR_KLASS = (RUBY_VERSION >= '1.9') ? Enumerator : Enumerable::Enumerator

It might even provide an opportunity to make use of Fibers. It’s going to be pretty sweet.

Next time, I’m getting off at Willoughby.