On Mon, 16 Oct 2023 10:19:17 GMT, Jorn Vernee <jver...@openjdk.org> wrote:
> Add the ability to pass heap segments to native code. This requires using > `Linker.Option.critical(true)` as a linker option. It has the same > limitations as normal critical calls, namely: upcalls into Java are not > allowed, and the native function should return relatively quickly. Heap > segments are exposed to native code through temporary native addresses that > are valid for the duration of the native call. > > The motivation for this is supporting existing Java array-based APIs that > might have to pass multi-megabyte size arrays to native code, and are current > relying on Get-/ReleasePrimitiveArrayCritical from JNI. Where making a copy > of the array would be overly prohibitive. > > Components of this patch: > > - New binding operator `SegmentBase`, which gets the base object of a > `MemorySegment`. > - Rename `UnboxAddress` to `SegmentOffset`. Add flag to specify whether > processing heap segments should be allowed. > - `CallArranger` impls use new binding operators when > `Linker.Option.critical(/* allowHeap= */ true)` is specified. > - `NativeMethodHandle`/`NativeEntryPoint` allow `Object` in their signatures. > - The object/oop + offset is exposed as temporary address to native code. > - Since we stay in the `_thread_in_Java` state, we can safely expose the oops > passed to the downcall stub to native code, without needing GCLocker. These > oops are valid until we poll for safepoint, which we never do (invoking pure > native code). > - Only x64 and AArch64 for now. > - I've refactored `ArgumentShuffle` in the C++ code to no longer rely on > callbacks to get the set of source and destination registers (using > `CallingConventionClosure`), but instead just rely on 2 equal size arrays > with source and destination registers. This allows filtering the input java > registers before passing them to `ArgumentShuffle`, which is required to > filter out registers holding segment offsets. Replacing placeholder registers > is also done as a separate pre-processing step now. See changes in: > https://github.com/openjdk/jdk/pull/16201/commits/d2b40f1117d63cc6d74e377bf88cdcf6d15ff866 > - I've factored out `DowncallStubGenerator` in the x64 and AArch64 code to > use a common `DowncallLinker::StubGenerator`. > - Fallback linker is also supported using JNI's > `GetPrimitiveArrayCritical`/`ReleasePrimitiveArrayCritical` > > Aside: fixed existing issue with `DowncallLinker` not properly acquiring > segments in interpreted mode. > > Numbers for the included benchmark on my machine are: > > > Benchmark (size) Mode Cnt ... This pull request has now been integrated. Changeset: 9c982707 Author: Jorn Vernee <jver...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/9c98270737cd2019f230e9359bb9298f8df2ca35 Stats: 2711 lines in 74 files changed: 1722 ins; 692 del; 297 mod 8254693: Add Panama feature to pass heap segments to native code Reviewed-by: mcimadamore, lucy, vlivanov ------------- PR: https://git.openjdk.org/jdk/pull/16201
