Java 9 build 148 causes trouble in Apache Lucene/Solr/Elasticsearch

[Peter Levart]

Hi Chris,


On 12/10/2016 06:11 PM, Chris Hegarty wrote:
> How about: Unsafe::deallocate(ByteBuffer directBuffer)?
>    http://cr.openjdk.java.net/~chegar/Unsafe_deallocate/

Apart from the fact that Unsafe is (was?) reserved for low-level stuff, 
I think this approach is reasonable. Is the method in 
jdk.internal.misc.Unsafe needed? You could add the method just to the 
sun.misc.Unsafe (to keep internal Unsafe free from hacks) and export the 
two packages selectively to jdk.unsupported.

> We could attempt to limit this to the direct buffer that "owns" the
> memory, i.e. not a duplicate or a slice, but I'm not sure it is worth
> it.

What you have here *is* limited to direct ByteBuffer(s) that "own" the 
memory. Derived buffer(s) (duplicated or sliced) do not have a Cleaner 
instance (they have an 'attachment' to keep the 1st-level buffer 
reachable while they are reachable). I would even make it more 
unforgiving by throwing an IAE if the passed-in buffer didn't have a 
Cleaner. In addition I would specify this behavior. For example:

"Deallocates the underlying memory associated with given directBuffer if 
the buffer was obtained from either {@link ByteBuffer#allocateDirect} or 
{@link FileChannel#map} methods. In any other case (when the buffer is 
not a direct buffer or was obtained by  {@link ByteBuffer#duplicate() 
duplicating} or {@link ByteBuffer#slice(int, int) slicing} a direct 
buffer), the method throws {@code IllegalArgumentException}.

Regards, Peter