On Jun 6, 2008, at 4:18 PM, Hamish Allan wrote:
On Fri, Jun 6, 2008 at 11:48 PM, Bill Bumgarner <[EMAIL PROTECTED]> wrote:The garbage collector does not currently interpret inner pointers as something that can keep an encapsulating object alive.But it's not the inner pointers I would expect to keep the object alive -- it's the fact that stack variables are root objects, and that NSData *data is still in the current stack frame.Fromhttp://developer.apple.com/documentation/Cocoa/Conceptual/GarbageCollection/Articles/gcEssentials.html : "The initial root set of objects is comprised of global variables, stack variables, and objects with external references. These objects are never considered as garbage. The root set is comprised of all objects reachable from root objects and all possible references found by examining the call stacks of every Cocoa thread." If the optimising compiler is marking variables past a certain point in the code block as being collectable because it doesn't think they're going to be used again before the stack frame is popped, this should be made explicit in the documentation (perhaps it is but I missed it). And is it really that important of an optimisation to make, if it's going to have side effects like this?
Yes, it is an exceedingly important optimization. Most likely, that stack slot is being reused by some variable later on.
I filed a bug asking that particular doc to be clarified-- <rdar://problem/5993075 >-- I can't remember if it is mentioned anywhere else, but it should definitely be mentioned there!
b.bum
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