On 01/09/13 05:55, Aleksey Shipilev wrote:
On 01/08/2013 08:33 PM, Doug Lea wrote:
However, the actual ThreadLocalRandom object is padded to avoid
memory contention (which wouldn't be necessary or useful if already
embedded withing Thread).
I'm tempted to disagree. While it is true most of the callers are
accessing Thread in the context of currentThread(), and most of the
Thread state is not updated, it can catastrophically break down once we
cram in the heavily updated fields.
I think that adding @Contended to Thread will require
some empirically-guided judgement. It is true
that a bunch of Thread objects packed adjacently may
(even now) memory-contend. But it is not a likely
scenario because of garbage-collector policies. They
start off with per-thread roots, so will not often
relocate different Thread objects adjacently.
We use various Thread subclasses in j.u.c that add
some thread-local-like state, and I haven't ever
traced a performance glitch to memory contention
among them. But it would not be too hard to create
empirical experiments to check this more systematically.
-Doug
