> See the JBS issue for an extended problem description. > > This patch changes the specification and implementation of > `MethodHandles::byteArrayViewVarHandle`, > `MethodHandles::byteBufferViewVarHandle`, `ByteBuffer::alignedSlice`, and > `ByteBuffer::alignmentOffset` to weaken the guarantees they make about the > alignment of Java array elements, in order to bring them in line with the > guarantees made by an arbitrary JVM implementation (which makes no guarantees > about array element alignment beyond them being aligned to their natural > alignment). > > - `MethodHandles::byteArrayViewVarHandle`: we can not guarantee any alignment > for the accesses. Which means we can only reliably support plain get and set > access modes. The javadoc text explaining which other access modes are > supported, or how to compute aligned offsets into the array is dropped, as it > is not guaranteed to be correct on all JVM implementations. The > implementation of the returned VarHandle is changed to throw an > `UnsupportedOperationException` for the unsupported access modes, as mandated > by the spec of `VarHandle` [1]. > > - `MethodHandles::byteBufferViewVarHandle`: the implementation/spec is > incorrect when accessing a heap buffer (wrapping a byte[]), for the same > reasons as `byteArrayViewVarHandle`. The spec is changed to specify that when > accessing a _heap buffer_, only plain get and set access modes are supported. > The implementation of the returned var handle is changed to throw an > `IllegalStateException` when an access is attempted on a heap buffer using an > access mode other than plain get or set. Note that we don't throw an outright > `UnsupportedOperationException` for this case, since whether the access modes > are supported depends on the byte buffer instance being used. > > - `ByteBuffer::alignedSlice` and `ByteBuffer::alignmentOffset`: The former > method depends directly on the latter for all its alignment computations. We > change the implementation of the latter method to throw an > `UnsupportedOperationException` for all unit sizes greater than 1, when the > buffer is non-direct. This change is largely covered by the existing > specification: > > > * @throws UnsupportedOperationException > * If the native platform does not guarantee stable alignment > offset > * values for the given unit size when managing the memory regions > * of buffers of the same kind as this buffer (direct or > * non-direct). For example, if garbage collection would result > * in the mo...
Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision: - Merge branch 'master' into AlignedOffset - Merge branch 'master' into AlignedOffset - Add api note pointing to alternatives for client that require non-plain access - simplify spec for alignmentOffset and alignedSlice - Merge note about misaligned access in byteBufferViewVarHandle - updated alignedSlice implNote as well - updated alignedOffset implNote - Use ISE for bbvvh instead of UOE - restore some tests for direct buffers - fix BAVV and BBVV impl and tests - ... and 2 more: https://git.openjdk.org/jdk/compare/a2273ed0...281deaa5 ------------- Changes: - all: https://git.openjdk.org/jdk/pull/16681/files - new: https://git.openjdk.org/jdk/pull/16681/files/eccf4f41..281deaa5 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=16681&range=02 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16681&range=01-02 Stats: 14804 lines in 723 files changed: 8780 ins; 2698 del; 3326 mod Patch: https://git.openjdk.org/jdk/pull/16681.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/16681/head:pull/16681 PR: https://git.openjdk.org/jdk/pull/16681
