[concurrency-interest] RFR: 8065804: JEP171:Clarifications/corrections for fence intrinsics

[Martin Buchholz]

On Tue, Dec 9, 2014 at 12:04 PM, Oleksandr Otenko
<oleksandr.otenko at oracle.com> wrote:
> On 26/11/2014 02:04, Hans Boehm wrote:
>>
>> To be concrete here, on Power, loads can normally be ordered by an address
>> dependency or light-weight fence (lwsync).  However, neither is enough to
>> prevent the questionable outcome for IRIW, since it doesn't ensure that the
>> stores in T1 and T2 will be made visible to other threads in a consistent
>> order.  That outcome can be prevented by using heavyweight fences (sync)
>> instructions between the loads instead.
>
>
> Why would they need fences between loads instead of syncing the order of
> stores?

Well explained by
http://www.cl.cam.ac.uk/~pes20/ppc-supplemental/test7.pdf