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
