The following issue came up during the code review cycle for the following:

JDK-8047104 cleanup misc issues prior to Contended Locking
                reorder and cache line bucket

On 6/20/14 9:23 AM, Daniel D. Daugherty wrote:
>
>> A few nits and queries and one more significant issue, which happens to be first:
>>
>> src/share/vm/runtime/atomic.hpp
>>
>> + // add* provide full bidirectional fence, i.e. storeload/read-modify-write/storeload
>>
>> That's not a "full bi-directional fence". A fence is: loadLoad|loadStore|storeLoad|storeStore - as per orderAccess.hpp. The cmpxchg wording:
>>
>> "Guarantees a two-way memory barrier across the cmpxchg. I.e., it's really a 'fence_cmpxchg_acquire'."
>>
>> was accurate in terms of required behaviour for cmpxchg. Whether the fence and acquire needed to be explicit depends on the platform.
>>
>> It is also not clear to me that other than cmpxchg* those atomic ops need "full bi-directional fences", or whether the current implementations actually provide them.
>
> This item will take some research to resolve so I'll have to reply
> again on this one later.

We've been trying to reach closure on the new wording for atomic.hpp
in off-thread e-mails for almost two weeks. At this point, I'm dropping
the atomic.hpp changes from this bug fix (8047104). Changes to the
wording in atomic.hpp may happen in a future Contended Locking bucket,
but for now it's not happening.