[foreign-memaccess+abi] RFR: Improve NIO channel support for buffer views over segments [v3]

[Chris Hegarty]

On Thu, 22 Apr 2021 11:36:32 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Chris Hegarty has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Resolve outstanding TODO in MemoryScope spec
>
> src/java.base/share/classes/java/nio/Buffer.java line 828:
> 
>> 826:                 public Scope.Handle acquireScope(Buffer buffer, boolean async) {
>> 827:                     var scope = buffer.scope();
>> 828:                     if (scope == null || scope.isImplicit()) {
> 
> do you still need the null handling (both here and in IOUtil) ? We just return a singleton now for implicit scope, so I think you can make the code more regular w/o losing any performance.

The null check is still needed - for "regular" buffers (that do not have a scope).

The `isImplicit` check can probably be removed. It is an unproven mirco-optimization to avoid the bloat of chaining unnecessary handles. It could be removed, and dropped altogether or pushed into the IOUtil code that does the chaining ( do not create a new Releaser for a handle that we've seen before, I assume handles can be compared by identity? )  Maybe I'll just drop this, and revisit later when benchmarking.

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PR: https://git.openjdk.java.net/panama-foreign/pull/512