our app has since long time dealt with multiple threads and QCRenderer, and we've worked around the issues that this implied (see Technical Q&A 1538 - http://developer.apple.com/mac/library/qa/qa2008/qa1538.html ).
Now, we're intrigued by the power and simplicity that Grand Central Dispatch would bring to our code: still, it's my understanding that we surrender the tight control over which-thread-does-what, that's vital to avoid the #1538 issues. Admittedly, I haven't explored GCD enough to know if there are ways to work the way we need: has anyone tried this, and how does that come out? Or, is the issue solved in Snow Leopard?
My current experience is that QuickTime issues have not been solved. So movie-using compositions may be problematic (checking under the hood, it looks like they maybe switched to QuickTimeX internally, so maybe there's some hope?) -- as usual, doing a test will give you usable results faster than asking on the lists :/
You still have control over which threads do what, in certain cases with GCD -- for example, dispatch_get_main_queue() is always going to happen on the main thread (of course, you lose concurrency when you use this queue). I'm not sure if dispatch groups keep threads around, or if you have to keep the queue "full" (always busy, never idle) to keep the thread around.
I'd highly recommend doing some tests, and firing up instruments to see if you encounter any problems (exceptions/crashes, or memory leaks) -- dispatch stuff is cake to add, so testing shouldn't be too painful.
That said, if you've already worked around the threading issues, and already have a successful multithreaded implementation, I'm not sure what benefits you'll get from GCD (other than automatic threadpool management, which is pleasant but not a show-stopper). I don't know your usage/needs, so maybe you would benefit, but you'll have to profile to figure that out.
-- [ christopher wright ] [email protected] http://kineme.net/
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