小编Vla*_* G.的帖子

当我测试直接java.nio.ByteBuffer的读取性能时,我注意到绝对读取的平均速度比相对读取快2倍.此外,如果我比较相对与绝对读取的源代码,除了相对读取维护和内部计数器之外,代码几乎相同.我想知道为什么我在速度上看到如此大的差异？

以下是我的JMH基准测试的源代码:

public class DirectByteBufferReadBenchmark {

    private static final int OBJ_SIZE = 8 + 4 + 1;
    private static final int NUM_ELEM = 10_000_000;

    @State(Scope.Benchmark)
    public static class Data {

        private ByteBuffer directByteBuffer;

        @Setup
        public void setup() {
            directByteBuffer = ByteBuffer.allocateDirect(OBJ_SIZE * NUM_ELEM);
            for (int i = 0; i < NUM_ELEM; i++) {
                directByteBuffer.putLong(i);
                directByteBuffer.putInt(i);
                directByteBuffer.put((byte) (i & 1));
            }
        }
    }



    @Benchmark
    @BenchmarkMode(Mode.Throughput)
    @OutputTimeUnit(TimeUnit.SECONDS)
    public long testReadAbsolute(Data d) throws InterruptedException {
        long val = 0l;
        for (int i = …

我不小心从Kamon Monitoring工具中遇到了Striped64.java类.在第95行,我发现了这个评论:

JVM intrinsics note: It would be possible to use a release-only
form of CAS here, if it were provided.

虽然我理解CAS是什么,但我无法找出CAS的唯一形式.有人可以对此有所了解吗？