Re: Named shared memory without synchronization
"Dan Schwartz" <DanSchwartz@discussions.microsoft.com> wrote in message
news:7F01C672-A048-4071-9A4E-EAF30484E682@microsoft.com
"Ben Voigt" wrote:
wouldn't this be atomic?
LOCK DEC ptr [eax]
Of course the compiler isn't required to generate the LOCK prefix...
with volatile would it be forbidden to?
Since I only speak "archaic" x86 assembly, I just have to ask, is the
LOCK prefix providing the memory barrier mentioned earlier?
Probably. x86 does not need memory barriers, it features strong cache
coherency. I'm not sure about 64-bit architectures (that is, I'm sure
they need memory barriers, but I'm not sure whether LOCK prefix provides
one or not).
In any case, the way to get the compiler to generate LOCK-prefixed
instruction is to use InterlockedDecrement or other Interlocked*
primitives. The documentation explicitly states that Interlocked*
functions issue all the necessary barriers, so why not rely on the
compiler to do the right thing (whether by emitting LOCK or any other
necessary instructions)?
--
With best wishes,
Igor Tandetnik
With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925