On Mon, 12 Oct 2020 11:42:04 GMT, Magnus Ihse Bursie <i...@openjdk.org> wrote:
>> Maurizio Cimadamore has updated the pull request incrementally with one >> additional commit since the last revision: >> >> Tweak referenced to MemoryAddressProxy in Utils.java > > Build changes look good. I've just uploaded a biggie update to the foreign memory access support. While doing performance evaluation, we have realized that mixing a multi-level hierarchy (`MappedMemorySegment extends MemorySegments`) with exact invoke semantics of `VarHandle` and `MethodHandle` is not a good match and can lead to great performance degradation for seemingly "correct" code. While some of this can be attributed to the `VarHandle` API, or to the fact that the so called "generic" invocation path should not be that slow in case where the parameters are clearly related, it seems smelly that a primitive API such as `MemorySegment` should give raise to such issues. We have therefore decided to drop the `MappedMemorySegment` - this means that there's only one memory segment type users can deal with: `MemorySegment` - and no chance for mistakes. Of course `MappedMemorySegment` has been primarily introduces to allow for operations which were previously possible on `MappedByteBuffer` such as `force`. To support these use cases, a separate class has been introduced, namely `MappedMemorySegments` (note the trailing `S`). This class contains a bunch of static methods which can be used to achieve the desired effects, without polluting the `MemorySegment` API. A new method has been added on `MemorySegment` which returns an optional file descriptor; this might be useful for clients which want to guess whether a segment is in fact a mapped segment, or if they need (e.g. in Windows) the file descriptor to do some other kind of low level op. I think this approach is more true to the goals and spirit of the Foreign Memory Access API, and it also offers some ways to improve over the existing API: for instance, the only reason why the `MemorySegment::spliterator` method was a static method was that we needed inference, so that we could return either a `Spliterator<MemorySegment>` or a `Spliterator<MappedMemorySgement>`. All of that is gone now, so the method can return to be what it morally always has been: an instance method on `MemorySegment`. Updated javadoc: http://cr.openjdk.java.net/~mcimadamore/8254162_v2/javadoc/jdk/incubator/foreign/package-summary.html Updated specdiff: http://cr.openjdk.java.net/~mcimadamore/8254162_v2/specdiff/overview-summary.html ------------- PR: https://git.openjdk.java.net/jdk/pull/548
