Magnus Hagander wrote:
> >We don't need the cancelConnLock if this is done properly (at least,
> >assuming that storing a pointer is atomic, which seems reasonable).
>
> Are you sure about this?
> Per what docs I have, storing a pointer should always be atomic.
> exchanging two pointers are not, which is why at least win32 provides a
> specific function to do that (InterlockedExchangePointer).
You can't even assume a pointer write is atomic to all threads if you
have multiple CPUs. Assume two CPU's. Even if CPU 1 writes the pointer
atomically, there is no guarantee that the other CPU will see the change
at the same time. To guarantee it, you need a memory barrier like a
lock/unlock. Some CPU systems guarantee memory conherency for memory
operations, but some do not.
It is temping to think that if one CPU can write a value atomically then
the other CPU will also see it at the same time, but that isn't
guaranteed.
For the hardware issues see:
http://www.javaworld.com/javaworld/jw-02-2001/jw-0209-toolbox.html
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