RFR: 8318966: Some methods make promises about Java array element alignment that are too strong

[Jorn Vernee]

On Thu, 16 Nov 2023 18:52:03 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/invoke/MethodHandles.java line 4610:
>> 
>>> 4608:      * {@link Double#doubleToRawLongBits}, respectively).
>>> 4609:      * <p>
>>> 4610:      * Access to heap byte buffers is always unaligned.
>> 
>> I recommend merging that sentence into the paragraph on heap byte buffers e.g.:
>>> For direct buffers, access of the bytes at an index is always misaligned. As a result only the plain...
>
> But... surely if I'm just accessing bytes the access cannot possibly be mis-aligned?

Right. I think there is a difference between 'unaligned' and 'misaligned'. Unaligned means there is no effort made to align the access (so it _may_ be misaligned). Misaligned means _definitely not_ aligned. At least, that is my interpretation.

This is what I wrote in the latest version:


     * For heap byte buffers, access is always unaligned. As a result, only the plain
     * {@linkplain VarHandle.AccessMode#GET get}
     * and {@linkplain VarHandle.AccessMode#SET set} access modes are supported by the
     * returned var handle. For all other access modes, an {@link IllegalStateException}
     * will be thrown.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16681#discussion_r1396215821