I’ve had an Event library as part of Rosella almost since that project began. I was inspired by a few other publish/subscribe systems I had been working with at the time and put together a relatively simple variant for Parrot. However, while I’ve been pretty happy with other things I’ve done in Rosella, I have not been happy with the Event library. I rewrote it a few times, but could never really get it working the way I wanted it to work. I let it sit for a while and focused on other projects instead.

Now, with the advent of Green Threads in Parrot, I’ve decided to go back and give the Event library a second look. Anything I can do to utilize and exercise the new green threads functionality will be a plus, and it finally gives me real motivation to go back and do eventing the right way. As of this week I have rewritten the library and have the basics of it available for use.

In the most simple usage, you create an Event object with a callback:

var event = new Rosella.Event();
event.subscribe("test subscriber", function(p) { ... }, "immediate");

Each subscriber gets a string name and a callback. The third argument to the subscribe method is the name of the dispatcher to use. The immediate dispatcher executes the callback immediately in line during the publish method. The “task” dispatcher schedules the callback to execute as a green thread. Also available, but not currently implemented, is a “thread” dispatcher which will dispatch the callback to a new worker thread. Once Parrot has thread support added (and we’re not too far off now), I’ll finish up that last option.

Here is a short example:

var event = new Rosella.Event();
event.subscribe("foo", function(p) { say("in foo"); }, "task");
event.subscribe("bar", function(p) { say("in bar"); }, "immediate");

…And the output, on my system:

in bar
in foo

So that’s not too shabby, and it’s a really easy way to use Parrot’s new green threads from the safety of Winxed and Rosella. There are a few more details I want to iron out still, and the library needs to be a lot more flexible to really fit in with the rest of the Rosella fold. I suspect in a few days I’ll declare the rewrite to be a stable part of Rosella.

In related news, hacker nine is still hard at work on the new threading implementation. I’ve been following along with some of his work and am starting to get pretty excited about it. He’s been following some of my designs and ideas pretty closely, and it’s all actually (surprisingly) working out for him. Whether he sticks with that design or needs to improvise to get passed some road blocks is for him to decide as he progresses.

I’ve done a little work trying to port the green threads implementation to work on windows, but am hampered because I don’t have a windows machine available to do any serious testing or developing on. My procedure right now is to write code at home on my laptop and try to test it on my windows machine at work. As you can imagine, for somebody as accustomed to a rapid iterative development cycle as myself, that kind of progress is slow and stultifying. If I do end up getting a new computer sometime soon, I might be able to pick up some speed. I hope to have green threads working on windows before the 3.11 release, but can’t make any promises considering my current development velocity on that project.

I have a few other ideas of things to add to Rosella to facilitate tasks and threading, but I think I am going to wait until Parrot has threads to really pursue anything else. Right now, it’s cool enough to have green threads working, and have an eventing library that is worth using.