RFR: 8310843: Reimplement ByteArray and ByteArrayLittleEndian with Unsafe [v2]

[Shaojin Wen]

On Mon, 10 Jun 2024 03:51:40 GMT, Glavo <duke at openjdk.org> wrote:

>> Things have changed since https://github.com/openjdk/jdk/pull/14636 was closed, so let me reopen it.
>> 
>> https://github.com/openjdk/jdk/pull/15386 confirmed that `VarHandle` in BALE caused a startup regression. In order to not have any more revert patches, it makes sense to optimize BALE.
>> 
>> The optimization of https://github.com/openjdk/jdk/pull/16245 allows the traditional expression to have good performance, but BA and BALE save us from having to copy these lengthy expressions everywhere. So it makes sense to keep them.
>> 
>> Now here's the question, should I rewrite this PR without `Unsafe`? I'll do some research (e.g. does `Unsafe` have better performance during warmup?), but I'd also like to take some advice.
>
> Glavo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update copyright

#16245 combining values ​​into larger store, Instead of using Unsafe, can we implement it as follows, similar to the early versions of java.nio.Bits?


class ByteArrayLittleEndian {
    // ...
    public static void setInt(byte[] array, int offset, int value) {
        array[offset    ] = (byte)  value;
        array[offset + 1] = (byte) (value >> 8);
        array[offset + 2] = (byte) (value >> 16);
        array[offset + 3] = (byte) (value >> 24);
    }

	public static void setLong(byte[] bytes, int off, long value) {
        array[offset]     = (byte)  value;
        array[offset + 1] = (byte) (value >> 8);
        array[offset + 2] = (byte) (value >> 16);
        array[offset + 3] = (byte) (value >> 24);
        array[offset + 4] = (byte) (value >> 32);
        array[offset + 5] = (byte) (value >> 40);
        array[offset + 6] = (byte) (value >> 48);
        array[offset + 7] = (byte) (value >> 56);
    }
    // ...
}

-------------

PR Comment: https://git.openjdk.org/jdk/pull/19616#issuecomment-2158447800