On Thu, 1 Feb 2024 20:10:29 GMT, Jorn Vernee <jver...@openjdk.org> wrote:
>> 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... > > 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 11 additional > commits since the last revision: > > - 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 > - regen test files > - ... and 1 more: https://git.openjdk.org/jdk/compare/da4eca34...eccf4f41 Marked as reviewed by mcimadamore (Reviewer). ------------- PR Review: https://git.openjdk.org/jdk/pull/16681#pullrequestreview-1857716614
