On Oct 28, 2010, at 9:16 AM, Jonny Taylor wrote: >> Note that sending notifications to other threads while holding locks in the >> current thread (or queue) is rife with danger & fragility. It is great way >> to create deadlocks and, if not, to end up with a solution that has all the >> maintenance costs of multi-threaded code combined with all the performance >> wins of single threaded execution.... > My situation is that I am receiving camera frames on a background thread, and > need a way of informing various windows that their displays should be updated > to reflect the fact that a new frame has been received. This GUI work needs > to be done on the main thread (I believe...). In addition, I take advantage > of the coalescing features of notifications to avoid unnecessary updates. > Thus I am keeping the currentFrame variable up to date in a threadsafe > manner, and then after updating it (and releasing the lock) I post a > notification to the main queue, with coalescing. Does that sound like a > reasonable approach? > > I definitely need to access currentFrame in a threadsafe manner, but > hopefully my description shows that the multithreaded relationship for the > notifications and variable updates is not there for performance reasons, if > that makes sense. I am more than aware of the trouble multithreading brings, > but the nature of the code makes it pretty unavoidable.
The best way to access something in a threadsafe manner is to only access it from one thread at a time without locking. And the best way to do that is to perpetuate the notion of thread ownership. When thread A is accessing the object, thread B not only does not access the object, thread B doesn't even have a reference to the object in its scope of execution. Not ever. When B -- likely the main thread -- needs to access the object, then A passes ownership to B, typically via GCD, operations or -performSelectorOnMainThread: b.bum _______________________________________________ Cocoa-dev mailing list ([email protected]) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [email protected]
