RFR: 8207851 JEP Draft: Support ByteBuffer mapped over non-volatile memory

[Alan Bateman]

On 20/08/2018 16:18, Andrew Dinn wrote:
> Hi Alan,
>
> Round 4:
>
> I have redrafted the JEP and updated the implementation in the light of
> your last feedback:
>
>    JEP JIRA: https://bugs.openjdk.java.net/browse/JDK-8207851
>
>    Formatted JEP: http://openjdk.java.net/jeps/8207851
>
>    New webrev: http://cr.openjdk.java.net/~adinn/pmem/webrev.04/
>
>
The updated JEP looks much better.

I realize we've been through several iterations on this but I'm now 
wondering if the MappedByteBuffer is the right API. As you've shown, 
it's straight forward to map a region of NVM and use the existing API, 
I'm just not sure if it's the right API. I think I'd like to see a few 
examples of how the API might be used. ByteBuffers aren't intended for 
use by concurrent threads and I just wonder if the examples might need 
that. I also wonder if there is a possible connection with work in 
Project Panama and whether it's worth exploring if its scopes and 
pointers could be used to backed by NVM. The Risks and Assumption 
section mentions the 2GB limit which is another reminder that the MBB 
API may not be the right API.

The 2-arg force method to msync a region make sense  although it might 
be more consistent for the second parameter to be the length than the 
end offset.

A detail for later is whether UOE might be more appropriate for 
implementations that do not support the XXX_PERSISTENT modes.

-Alan.