On Mar 6, 2012, at 1:51 PM, Jan E. Schotsman wrote:
> Hello,
>
> I have an array of progress values (number objects) for subprojects, from which I calculate the overall progress .
> The array is an atomic property of the project class.
>
> Is it safe to access this array from multiple threads, using methods like objectAtIndex and replaceObjectAtIndex?
(Resending since my original reply, written yesterday, still hasn’t posted; apologies if this ends up showing up twice on the list.)
It’s not; however, if you implement the KVO indexed accessors for to-many properties, described here:
https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/KeyValueCoding/Articles/AccessorConventions.html#//apple_ref/doc/uid/20002174-178830-BAJEDEFB
and guard each accessor with a mutex, spinlock, dispatch_sync, or something similar, you should then be able to use -mutableArrayValueForKey: to return an NSMutableArray proxy that you can use like an ordinary NSMutableArray, but which will call your now-atomic indexed accessors to get at the contents of the array. Just make sure all accessors are properly thread-safe and that none of them return the actual ivar backing the property, and you should be fine.
Charles
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