JDK 9 proposal: allocating ByteBuffers on heterogeneous memory

[Doug Lea]

On 03/31/2016 05:14 PM, Dohrmann, Steve wrote:
> This is a JDK 9 proposal to support allocation of direct java.nio.ByteBuffer
> instances backed by memory other than off-heap RAM.

I like it. Various kinds of heterogeneous memories are becoming more
common, and this seems like the simplest accommodation that at least
gets ByteBuffer functionality.

With such a simple API, it is hard to imagine fundamental problems
fitting to other heterogeneous systems, but it would still be great
if anyone dealing with non-Intel systems (TI/KeyStone?) could
sanity-check this.

I suspect some people would prefer a more elaborate SPI scheme,
but this seems fine to me:


> package java.nio;
>
> interface Memory { public ByteBuffer allocateByteBuffer(int size); }
>
> Developers would obtain instances of these Memory objects by calling public
> constructors on specific memory classes.  We propose having developers call
> constructors directly because it is a simple way to accommodate varying
> initialization requirements (e.g. partitioning) that specific memory
> instances may have.
>
> For uniformity, we propose mirroring the existing off-heap
> java.nio.ByteBuffer allocation through an off-heap RAM class that implements
> the Memory interface:
>
> package java.nio;
>
> public class OffHeapRAM implements Memory { @Override public ByteBuffer
> allocateByteBuffer(int size) { return ByteBuffer.allocateDirect(size); } }
>
> Uniform access could be extended to on-heap ByteBuffers with a class that
> wraps the non-direct allocation method in ByteBuffer:
>
> package java.nio;
>
> public class HeapRAM implements Memory { @Override public ByteBuffer
> allocateByteBuffer(int size) { return ByteBuffer.allocate(size); } }
>
> The 3 additions above are the only changes proposed.  Links to a bug report
> and to a JDK 9 patch containing these additions are shown below.  For sample
> code, we are also creating a class that implements the Memory interface for
> java.nio.ByteBuffers backed by Intel's 3D XPoint memory.
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8153111
>
> patch: http://cr.openjdk.java.net/~vdeshpande/8153111/webrev.00/
>
> While other useful capabilities in this space (e.g. persistent memory,
> process-shared memory) are being explored, they are specifically not
> addressed or proposed here.  We believe that supporting java.nio.ByteBuffer
> allocation on other memory spaces is sufficiently useful to propose it now
> for JDK 9.
>
> Please let us know if there is interest in this proposal and if you would
> like to sponsor a patch.
>
> Best regards, Steve Dohrmann
>
>