On 3/6/12 11:51 AM, 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?
OK, you don't have an *array* you have a *mutable array*. NSArray itself is perfectly thread safe. In short, no, NSMutableArray is NOT safe to use from multiple threads out of the box (https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Multithreading/ThreadSafetySummary/ThreadSafetySummary.html). You would have to implement your own locking/synchronization if this is an essential behavior. The "atomic" keyword actually provides only very minimal thread safety: it guarantees merely that other objects accessing your property won't get an incorrect value if the property is in the process of being set. Bill Bumgarner has an instructive blog post on this topic, explaining why "atomic" is not synonymous with "thread safe": http://www.friday.com/bbum/2008/01/13/objectivce-c-atomic-properties-threading-andor-custom-settergetter/ Since array mutations aren't going through the property setter, "atomic" doesn't help here even to that meager degree. Personally, I try to the maximum extent possible to make properties be of immutable types for exactly this reason. It allows you to centralize management of locking/synchronization thus wipe out a whole category of potential bugs. It also allows for, e.g., easier KVO and generally simpler code. -- Conrad Shultz Synthetiq Solutions www.synthetiqsolutions.com _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) 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: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
