谁帮忙看看这段 Java 并发代码

我开了 100 个线程用同一个 id 分别去请求这两个方法，把这 100 次方法执行时间的平均值取出来，并且相同的方法重复做了三次得到结果： a: 24907.9ms, b: 24831.1ms ，看结果方法 b 好一点，但这个差距是不是很小啊？

@Controller @RequestMapping("/bench/") public class BenchController { private static Object[] lockObj; rivate static AtomicReference<Integer>[] 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<Integer>(null); } } @RequestMapping("a") @ResponseBody public long a(int id) throws Exception { long start = System.currentTimeMillis(); int index = id % 100; synchronized (lockObj[index]) { Thread.sleep(500); } long result=System.currentTimeMillis() - start; System.out.println(result); return result; } @RequestMapping("b") @ResponseBody public long b(int id) throws Exception { long start = System.currentTimeMillis(); int index = id % 100; while (!locks[index].compareAndSet(null, id)) { } Thread.sleep(500); locks[index].compareAndSet(id, null); long result=System.currentTimeMillis() - start; System.out.println(result); return result; } }