Java 偏向锁测试

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JDK 1.8.0_60

import java.util.Random;import java.util.concurrent.*;/** * Created by Administrator on 2016/1/27. * JDK 1.8.0_65 */public class Test5 {    private static final int NTHREAD = 4;    private static final int COUNTER = 10000000;    private static Random random = new Random(123);    private static ExecutorService es1 = Executors.newSingleThreadExecutor();    private static ExecutorService es2 = Executors.newFixedThreadPool(NTHREAD);    private static ThreadLocal<Random> tl = new ThreadLocal<Random>() {        @Override        protected Random initialValue() {            return new Random(123);        }    };    private static class Task implements Callable<Long> {        private int mode = 0;        public Task(int mode) {            this.mode = mode;        }        public Random getRandom() {            if (mode == 0) {                return random;            } else if (mode == 1) {                return tl.get();            }else                return null;        }        @Override        public Long call() throws Exception {            long start = System.currentTimeMillis();            for(long i = 0; i < COUNTER; i++) {                getRandom().nextInt();            }            long end = System.currentTimeMillis();            System.out.println(Thread.currentThread().getName() + "spend " + (end - start) + " ms");            return (end - start);        }    }    public static void main(String... args) throws ExecutionException, InterruptedException {        Future<Long> futs1 = es1.submit(new Task(0));        long time1 = 0;        time1 += futs1.get();        System.out.println("+UseBiasedLocking : " + time1 + " ms");        //System.out.println("-UseBiasedLocking : " + time1 + " ms");        es1.shutdown();        Future<Long>[] futs2 = new Future[NTHREAD];        for(int i = 0; i  < NTHREAD ; i++) {            futs2[i] = es2.submit(new Task(0));        }        long time2 = 0;        for(int i = 0; i  < NTHREAD ; i++) {            time2 += futs2[i].get();        }        System.out.println("N Thread access one Random instance : " + time2 + " ms");        for(int i = 0; i  < NTHREAD ; i++) {            futs2[i] = es2.submit(new Task(1));        }        long time3 = 0;        for(int i = 0; i  < NTHREAD ; i++) {            time3 += futs2[i].get();        }        System.out.println("ThreadLocal access one Random instance : " + time3 + " ms");        es2.shutdown();    }}

//可以明显的看到使用偏向锁，单线程时间减少，但是多线程时间延长
pool-1-thread-1spend 563 ms
+UseBiasedLocking : 563 ms

pool-2-thread-4spend 2121 ms
pool-2-thread-2spend 2130 ms
pool-2-thread-3spend 2309 ms
pool-2-thread-1spend 2310 ms
N Thread access one Random instance : 8870 ms
pool-2-thread-2spend 1563 ms
pool-2-thread-4spend 1714 ms
pool-2-thread-1spend 1603 ms
pool-2-thread-3spend 1784 ms
ThreadLocal access one Random instance : 6664 ms

//可以明显的看到禁用偏向锁，单线程时间延长，但是多线程时间减少
-UseBiasedLocking
pool-1-thread-1spend 760 ms
-UseBiasedLocking : 760 ms

pool-2-thread-1spend 1153 ms
pool-2-thread-3spend 1141 ms
pool-2-thread-4spend 1713 ms
pool-2-thread-2spend 2081 ms
N Thread access one Random instance : 6088 ms
pool-2-thread-1spend 1131 ms
pool-2-thread-3spend 1027 ms
pool-2-thread-4spend 1463 ms
pool-2-thread-2spend 1648 ms
ThreadLocal access one Random instance : 5269 ms

-UseBiasedLocking
pool-1-thread-1spend 760 ms
-UseBiasedLocking : 760 ms

pool-2-thread-1spend 1153 ms
pool-2-thread-3spend 1141 ms
pool-2-thread-4spend 1713 ms
pool-2-thread-2spend 2081 ms
N Thread access one Random instance : 6088 ms
pool-2-thread-1spend 1131 ms
pool-2-thread-3spend 1027 ms
pool-2-thread-4spend 1463 ms
pool-2-thread-2spend 1648 ms
ThreadLocal access one Random instance : 5269 ms

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