RFR(S) 8067331: Zero: Atomic::xchg and Atomic::xchg_ptr need full memory barrier

David Holmes david.holmes at oracle.com
Mon Jan 5 02:21:48 UTC 2015

Hi Severin,

Sorry this slipped through the cracks before the holidays.

On 16/12/2014 1:09 AM, Severin Gehwolf wrote:
> Hi,
> Could someone please review and sponsor the following change?
> bug: https://bugs.openjdk.java.net/browse/JDK-8067331
> webrev:
> http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8067331/webrev.02/
> The issue is that all atomic operations are expected to be full memory
> barriers, but two implementations of the Zero variant JVM - Atomic::xchg
> and Atomic::xchg_ptr - use GCC's built-in __sync_lock_test_and_set which
> is an acquire barrier only. The fix adds full memory barriers manually
> for those.
> Thoughts?

Looks completely consistent with what I just saw in the aarch64 port code.

I can sponsor this but we still need a second review.


> Cheers,
> Severin

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