[Openmcl-devel] [openmcl-devel] atomic-incf
David L. Rager
ragerdl at cs.utexas.edu
Thu Oct 15 17:42:05 EDT 2009
I'm pretty sure I understand the multi-threading issue. Even if it
were a single CISC instruction, there would be no "atomicity"
guarantee without the lock on the memory address (where the lock
prohibits reading/writing of that address).
> ATOMIC-INCF basically tries to guarantee that the
> read-modify-write sequence happens atomically.
> I think that we could actually implement it as
> (addq ($ fixnumone) (@ loc))
> (movq increment-by (% reg))
> (addq (% reg) (@ loc))
> on x86; we actually do a similar compare-and-swap loop on both
So do we know whether the atomic-incf in CCL version 1.3 of
x86-misc.lisp is thread-safe? I'm happy to go read more about the X86
assembly "specification" in order to better understand the code myself
if that's what's required.
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