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From: Chris Thomasson (cristom_at_[hidden])
Date: 2006-10-21 23:37:46

"Chris Thomasson" <cristom_at_[hidden]> wrote in message
> "Peter Dimov" <pdimov_at_[hidden]> wrote in message
> news:000601c6f582$10c92890$6507a8c0_at_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...


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