下面代码里无锁和有锁比是更好的实现吗？我用jmeter每秒20个请求，无锁代码执行test()里的sleep操作的输出大部分与500毫秒差别巨大，而有锁代码的输出基本就是500毫秒相差1，2毫秒的样子，这个问题很怪异啊....

@Controller
@RequestMapping("/bench/")
public class BenchController {

    @Autowired
    private FlowService flowService;

    private static Object[] lockObj;
    private static AtomicReference[] locks;

    static {
        lockObj = new Object[100];
        for (int i = 0; i < lockObj.length; i++) {
            lockObj[i] = new Object();
        }

        locks = new AtomicReference[100];
        for (int i = 0; i < locks.length; i++) {
            locks[i] = new AtomicReference(null);
        }
    }

    @RequestMapping("a")
    @ResponseBody
    public long a(int id) throws Exception {
        long start = System.currentTimeMillis();
        int index = id % 100;
        long inner=0;
        synchronized (lockObj[index]) {
            inner=test();
        }
        long result = System.currentTimeMillis() - start;
        System.out.println("all: "+result+" inner: "+inner);
        return result;
    }

    @RequestMapping("b")
    @ResponseBody
    public long b(int id) throws Exception {
        long start = System.currentTimeMillis();
        AtomicReference lock=locks[id % 100];
        while (!lock.compareAndSet(null, id)) {}
        long inner=test();
        boolean flag=lock.compareAndSet(id, null);
        long result = System.currentTimeMillis() - start;
        System.out.println("all: "+result+" inner: "+inner+" flag:"+flag);
        return result;
    }

    public long test()throws Exception{
        long innerstart = System.currentTimeMillis();
        Thread.sleep(500);
        System.out.println(System.currentTimeMillis()-innerstart);
        return System.currentTimeMillis()-innerstart;
    }
}