"Chris Thomasson" <cristom@comcast.net> wrote in message news:ehenuk$if2$1@sea.gmane.org...
"Peter Dimov" <pdimov@mmltd.net> wrote in message news:000601c6f582$10c92890$6507a8c0@pdimov2...
Chris Thomasson wrote:
The basic technique for 'copying' is as follows:
[...] I need to clarify one thing here
A refcount object drop to zero condition means that there are no shared locations that contain any pointers to it. Any increment threads that have loaded pointers, will fail when they reload-and-compare.
[...]
If one gets through, and their compare succeeds, it doesn't matter because it has already locked the associated spinlock, so it has exclusive access to the refcount. Since its reload and compare succeeded, that means it happened before any decrement thread got to execute; swaps happen before decrements (e.g., swap shared loc with 0, dec the old ptr). A decrement thread will always lock the spinlock before it calls the destructor, so it will wait for the one that got through the compare logic... ^^^^^^^^^^^^^^^^^
I forgot to mention that the thread that got through the gap between the decrement to 0, and the lock, it will be subject to the compare logic and/or the logic the prevents a copy when a refcount value get increments and its previous value was less than 1. I know this is a bit tricky logic, however I believe that if you examine some more you will find it to be correct... ;^)