> 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 ...
Jorn Vernee has updated the pull request incrementally with three additional commits since the last revision: - add stub size stress test for allowHeap - RISC-V impl - remove leftover debug log line ------------- Changes: - all: https://git.openjdk.org/jdk/pull/16201/files - new: https://git.openjdk.org/jdk/pull/16201/files/65bd8d83..dd9e9741 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=16201&range=07 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16201&range=06-07 Stats: 151 lines in 4 files changed: 74 ins; 66 del; 11 mod Patch: https://git.openjdk.org/jdk/pull/16201.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/16201/head:pull/16201 PR: https://git.openjdk.org/jdk/pull/16201
