RFR: 8181085: Race condition in method resolution may produce spurious NullPointerException

[Andrew Dinn]

Hi David,

On 26/05/17 10:20, David Holmes wrote:
> Hi Andrew,
> 
> On 26/05/2017 6:26 PM, Andrew Haley wrote:
>> On 26/05/17 03:20, David Holmes wrote:
>>> Any variable passed to an OrderAccess, or Atomic, function should be
>>> volatile to minimise the chances the C compiler will do something
>>> unexpected with it.
>>
>> That's not much more than paranoia, IMO.  If the barriers are strong
>> enough it'll be fine.  The problem was, I suppose, with old compilers
>> which didn't handle memory barriers properly, but we should be moving
>> towards standard ways of doing these things.  Standard atomics have
>> been available since C++11 (I think) and GCC has had support since long
>> before then.
> 
> The issue isn't just the barriers that might be involved inside
> orderAccess methods. If these variables are being used in racy lock-free
> code then they should be marked volatile to ensure other compiler
> optimizations don't interfere. Perhaps that is paranoia, but I'd rather
> a little harmless paranoia than try to debug what might otherwise go wrong.

I don't understand what you are suggesting here. How is such racy,
lock-free code ever going to work on architectures with weak memory models?

> ...

regards,


Andrew Dinn
-----------
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