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Re: ANNOUNCE: Submit Java Tasks to Grand Central Dispatch (GCDExecutorService)


On Oct 31, 2009, at 3:30 PM, Mike Swingler wrote:

I don't see anything wrong with leaving the system provided GCD dispatch threads attached to the JVM, unless you are concerned about which security/app context thread group those threads will be attached to. I would say for simplicity, you could simply not care and live with no thread classloader or ask for the system classloader to be associated with the native threads forever. If the AppContext, the thread classloader, or the security context of the thread group matters, then you'll have to attach/detach on every single invocation.

Ah, you've just made me realize there's been an error in my thinking about GCD. I've been assuming without questioning it that it is, at its core, an operating system wide thread pool, where the OS manages some total pool of available threads and these can do work for any application. In my imagination,  one minute a thread might be servicing Java and another minute it might be servicing Finder.

But that's nonsense. Somehow I'd read all this talk of system wide load management and forgotten that a thread lives within a single process. Of course, GCD could be implemented on some other abstraction - processes, messages etc, but there'd be some fierce problems to solve moving arbitrary blocks of code and data around between processes! And to do it securely, not plausible!?!

So of course, however few or many threads GCD creates for the JVM belong to the JVM process. And following on from that thought, given you think it's OK, then indeed, why not let them stay attached to the JVM until they die? If there is a tradeoff to me made what I could do is give the GCDExecutor a boolean constructor parameter to let the caller decide, but even that might just be adding unnecessary complexity.

Thanks again - I'll incorporate your feedback this week as time allows.

AndyT (lordpixel - the cat who walks through walls)
A little bigger on the inside

(see you later space cowboy, you can't take the sky from me)

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