On Jun 27, 2008, at 12:31 PM, John Engelhart wrote:
Lesson #1: If you have any interest in performance, you must avoid, at all costs, "writing" to a __strong pointer.
If this were the case, all assignments to instance variables would be exceptionally costly under GC. They are not -- applications run under GC can get quite good performance. Assignment through write barriers does have a cost, yes, but that cost is amortized by the fact that the GC system can use the generation information provided by using write barriers to be more efficient.
Furthermore *every* assignment to an object pointer is effectively a __strong assignment. If your performance assumptions were true in the general case, you might expect to see everything that runs under GC perform at a fraction the speed it runs under non-GC, which isn't the case for the large application I work on.
And thus began yet another exciting adventure with the GC system that caused me to waste several days.
You could ask for help on the list sooner rather than spending days and days beating your head against something like this...
I'll reiterate what I've said in the past, though: Objective-C Garbage Collection works quite well in Leopard, and applications large and small can use it quite effectively. I generally don't create new Cocoa projects these days without turning on Objective-C GC support. If you encounter bugs, file them.
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