Re: atomic memory_order with command or with fence

Pete Becker <>
Thu, 31 May 2012 16:05:42 -0700 (PDT)
On 2012-05-31 04:18:35 +0000, itaj sherman said:

On May 30, 5:21 am, Pete Becker <> wrote:

On 2012-05-30 00:39:27 +0000, itaj sherman said:

Right, it doesn't order x, I didn't mean for it to. The point was
for x to cause a synchronization (an optional one) on the
fences. So that stores that were sequenced before the release
fence, be certainly visible to loads that happen after the acquire

That's not quite right. The fence causes the synchronization. But the
only way for the second thread to know that the synchronization has
occurred is to see the value that the first thread wrote into x. So
from a coding perspective, once you read the correct value, you know
that all the stuff that happened before the fence is visible in your
thread. If you haven't read the correct value it could simply because
the other thread hasn't gotten there yet.

Oh, I get what you mean, I only meant "x could imply synchronization"
not "cause", by that the pair of store and load (which read the stored
value) imply that the fences synchronize, per 29.8-p2

Sorry, I was a bit sloppy. The fence enforces visibility, which is what
I referred to as "synchronization". You used "synchronization" in a
higher-level sense, as in, ensuring that you've got visibility before


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