Re: 32-bit memory accesses on dual-core dual-Xeon processors

From:

"Bruno van Dooren [MVP VC++]" <bruno_nos_pam_van_dooren@hotmail.com>

Newsgroups:

microsoft.public.vc.language

Date:

Wed, 3 Jan 2007 21:39:44 +0100

Message-ID:

<uaNOPd3LHHA.1248@TK2MSFTNGP03.phx.gbl>

I have an implementation for a circular buffer (a fixed-sized queue of
pointers) where there is only one producer and one consumer, each running
independently in different threads. There is currently no protection
(locking) because there are no variables that can be written to by both
threads simultaneously. The head and/or tail could be read by one thread
and
written by the other, but logically, there are no issues as long as whole
32-bit quantities can be accessed.

Is there anything wrong with the assumptions I've made, especially when
the
code is run on dual-core dual-Xeon processors? Is memory on these 64-bit
processors accessed in such a way that there could be a memory corruption?

I have used that construct myself. it is perfectly safe on 32 bit platforms
or 64 bit platforms because the reads and writes of a 32 bit variable are
executed atomically. i.e. you won't read a half written 32 bit variable.
cache coherency should be taken care of by the chipset / cpus.

So yeah, it is safe - barring other programming errors of course.

--

Kind regards,
    Bruno van Dooren
    bruno_nos_pam_van_dooren@hotmail.com
    Remove only "_nos_pam"