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Thoughts on development, user-centered design, code, etc. by Paul Robertson

AS3 Concurrency/Workers use cases, best practices, and link roundup

Leif Wells responded to my presentation slides on ActionScript 3 Workers/Concurrency with a great question:

Is there a discussion somewhere on practical use cases for AS3 Workers? Best Practices? (Leif Wells on Twitter)

Use cases

I talked some about practical use cases in my presentation. The summary version is this: “any time you find yourself wishing you could make your code run asynchronously, consider putting it in a worker.” In other words, any time you’ve got code that’s doing some sort of work that takes so long that it causes pauses or stuttering in your user interface, that’s a good candidate for a Worker. In particular if the code is something you’d rather do “in the background.” Here are some concrete examples:

  • text/data processing (e.g. the example I gave in the slides of loading an xml file and looping over all the nodes to create an object graph)
  • visual/image/audio data processing (e.g. any image processing algorithm that isn’t already using PixelBender) – some examples are in the links below
  • Physics engine running in the background

Best practices

As for “best practices” that’s basically what I talked about in the section called “caveats” in slides 69-71. (These are also suggested and/or explicitly called out in the documentation.) The main suggestions I would make are:

  • Under normal circumstances, you shouldn’t use more than one or two background workers at most. Each worker is a full-blown instance of the ActionScript VM/runtime (without a visible stage). In essence you’re increasing memory use and (simultaneous, but distributed) processor use to trade off for not blocking your UI thread. Consider carefully if the cure is worse than the disease. (Remember that a single worker can do multiple operations – just not simultaneously.)
  • If you’re really done with a worker, terminate it to and the garbage collector will reclaim/free its memory.
  • Create a separate swf for your workers, rather than using the “same swf for main and worker” pattern. Many of the examples I link to below were created before Flash Builder 4.7 was released. Because of that, those examples tend to use the architecture of having a single swf file serve as both the main swf and the background worker SWF. Personally I strongly recommend against that just on general architectural principles. Before it was a matter of convenience – it’s a lot easier to test code if you only have to recompile one swf. In Flash Builder 4.7 they they added some nifty built-in features for creating and managing workers in projects, that’s no longer necessary because the IDE does the work for you =)

Links and resources

Leif’s question also made me realize that I’ve shared some links on Twitter about Workers, but it would be nice to compile them into a single post. So here is my collection of recommended links related to AS3 Workers:

Adobe documentation

  • Using workers for concurrency from the ActionScript 3.0 Developer’s Guide. In some ways this is a long-form version of my presentation. (Not surprising since I wrote both of them. =) he section on Understanding workers and concurrency has some of the same background as my presentation, and talks about best practices a bit. The other sections are more practical/hands on.
  • Worker class in the ActionScript Language Reference. I knew that most developers would go here first to learn about using workers, so I tried to give the class description enough content to help someone get started and find the important info they need.