[concurrency-interest] @Contended (JEP-142)

Kasper Nielsen kasperni at gmail.com
Tue Nov 27 13:46:25 EST 2012


Hi,

1)
Without having read Alekseys previous post to hotspot-dev I would have had
a hard time figuring how the group stuff would work.
While the layout might not be identical on platforms with different
cache-line sizes. I think the examples might be worth including in the
javadoc


2)
I'm fine with sun.misc. But wouldn't it make sense to introduce a vm
package (for example, java.lang.vm) which contains vm/cpu integration
classes.
I'm specially thinking about things that probably inevitable will come at
some point: NUMA-aware information, control of object layout, cpu
information, gc integration.
The package would basically be _expert_ level only. But having having stuff
like that in one standard package people/organizations could easily use
simple tools to make sure rogue developers weren't using anything from the
package.

3)
It probably already is, but I'm just making sure
Instrumentation#getObjectSize() returns the correct number.

I know it is probably out of scope for Java 8 but some tools (without
requiring an agent class) for calculating the object size is missing. I lot
of projects goes through a lot of trouble to calculate the size. See for
example http://www.codespot.net/blog/2012/01/measuring-java-object-sizes/or
just google 'calculate java object size'. These alternative methods
are
only going to be more broken after introducing @Contended, especially the
reflection based once.

Perhaps adding the method #getObjectSize() to sun.misc.Unsafe for now would
help.


Cheers
  Kasper


On Tue, Nov 27, 2012 at 6:40 PM, Doug Lea <dl at cs.oswego.edu> wrote:

>
> Aleksey has been making progress on a hotspot implementation of
> the @Contended annotation. While this progresses, we'd also
> like continued feedback about the java-level information, guidance,
> examples, etc.
>
> As a compromise that helps avoid controversy about its status
> and specs, the @Contended annotation itself will probably be placed
> in sun.misc, not java.util.concurrent.*. A staging version of
> Contended.java is in our CVS though, with javadoc at:
>
> http://gee.cs.oswego.edu/dl/**jsr166/src/dl/sun/misc/sun/**
> misc/Contended.html<http://gee.cs.oswego.edu/dl/jsr166/src/dl/sun/misc/sun/misc/Contended.html>
>
> Any comments and suggestions will be welcome.
>
> -Doug
>
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