6647361: use Unsafe.put*Volatile methods to set final fields during default deserialization

[Doug Lea]

On 11/22/10 09:35, Rémi Forax wrote:
>> This is a patch to default deserialization so that it uses volatile-write when
>> setting final fields:
>> http://cr.openjdk.java.net/~alanb/6647361/webrev/
>>
>
> I wonder if we can't use putOrdered instead of putVolatile.
> In that case Field.set() should be changed too because it uses putVolatile.
>

Yes this will suffice. For some discussion about emulating
final, see the draft (NOT JDK7 (maybe 8)) Fences API
(http://gee.cs.oswego.edu/dl/jsr166/dist/docs/java/util/concurrent/atomic/Fences.html)
In fact if this API existed you could just use it (modulo
some JVM/platform-dependent tearing issues for long/double).
In the mean time, putOrdered suffices. But note that
putOrdered exists only for int, long, and volatile.
For the others you could just resort to the volatile form.

The cost savings of using these lighter fences are
platform dependent. On some Intel i7s, it might be
less than 10 cycles. On most processors, it is on the
order of 30. On older P4s (and PowerPC) it can be over 100.

-Doug