On Wed, Dec 19, 2012 at 4:28 PM, Peter Dimov <lists@pdimov.com> wrote:
Andrey Semashev wrote:
All uses of READ_BARRIER or WRITE_BARRIER seem wrong, though. READ_WRITE_BARRIER is needed in all places where these are used.
Why? The intention was to prevent outer reads and writes being reordered with the atomic op. Did I miss something?
The acquire/release semantics are not specific to reads or writes. An acquire load should prevent subsequent writes from being reordered so as to precede it, and a read barrier doesn't do that, I think.
I suppose you're right. I was under impression that _ReadBarrier and _WriteBarrier intrinsics were equivalent to the acquire and release compiler fences but reading their docs now this doesn't seem to be correct. Only _ReadWriteBarrier has the comment that the compiler doesn't reorder operations across it. Thank you, I will correct the code.