[concurrency-interest] padding in Exchanger

Vitaly Davidovich vitalyd at gmail.com
Tue Jan 17 11:13:36 EST 2012


I think it's semantics - if you sometimes allocate with 64/128 byte
alignment then if your object is smaller than 64/128 the rest of the space
is effectively padding.  Or are you saying you want an @Alignment
annotation instead so it's more general? What other uses of custom
alignment do you envision? Java is too high-level  and the underlying
hardware/platform too abstracted away for a general purpose custom
alignment hint, IMHO.

Sent from my phone
On Jan 17, 2012 10:56 AM, "Ruslan Cheremin" <cheremin at gmail.com> wrote:

> > Yes. As a practical matter though, until an @Contended attribute
> > or something like it is supported across JVMS (see list archives for
> > discussion), you cannot arrange reliable two-sided padding
> > for objects with mixed field types (ints, longs, refs that may be
> > either 32 or 64 bits, etc), so one-sided is the best you can do.
>
> By the way -- I was not thinking about @Contended as "make padding for
> me". It seems for me like padding is only dirty hack, since nothing
> better available. If I would control memory allocation (like JVM does)
> I just can allocate @Contended objects on 64 (128... etc) bytes
> boundary. I do not have to "pad" them -- nor both, nor one side. And I
> suppose @Contended implementation to do exactly this -- "use special
> allocator for objects of that type, which allocate them on cache line
> boundary"
>
> Am I wrong here?
>
>
> >
> > -Doug
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