子类集成父类调用父类的synchronized方法，多个线程调用时还是会顺序执行啊，不需要跟老师说的需要在子类中单独声明，为什么？

Question

@Slf4j
public class SyncTest {

    public void test1() {
        synchronized (this) {
            for (int i = 0; i < 10; i++) {
                log.info("test1 {}", i);
            }
        }
    }

    public synchronized void test2() {
        for (int i = 0; i < 10; i++) {
            log.info("test2 {}", i);
        }
    }
}

子类代码

@Slf4j
public class SyncTestSub extends SyncTest{

    public static void main(String[] args) {
        SyncTestSub sub = new SyncTestSub();
        ExecutorService executorService = Executors.newCachedThreadPool();
        executorService.execute(() ->
                {
                    sub.test2();
                }
        );
        executorService.execute(() ->
                {
                    sub.test2();
                }
        );

        executorService.execute(() ->
                {
                    sub.test2();
                }
        );
        executorService.shutdown();
    }
}

最终执行日志

00:52:46.175 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 0
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 1
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 2
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 3
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 4
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 5
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 6
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 7
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 8
00:52:46.178 [pool-1-thread-1] INFO com.lv.demo.concurrency.sync.SyncTest - test2 9
00:52:46.178 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 0
00:52:46.178 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 1
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 2
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 3
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 4
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 5
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 6
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 7
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 8
00:52:46.179 [pool-1-thread-3] INFO com.lv.demo.concurrency.sync.SyncTest - test2 9
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 0
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 1
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 2
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 3
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 4
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 5
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 6
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 7
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 8
00:52:46.179 [pool-1-thread-2] INFO com.lv.demo.concurrency.sync.SyncTest - test2 9

求解答

Answer 1

Jimin 2020-04-07 22:09:35

你好，目前这个例子可能表达不一定好，因为执行的太快了，可以带上sleep看下效果，太快了会导致线程不是并行执行

• 慕慕1561859 #1

  不是吧老师，我也是这种情况，子类继承了test2的同步方法

• 慕慕1561859 #2

  而且去掉父类的同步关键字，子类的test2变成随机执行了，我觉得直接继承夫类是可以将sych关键字继承过来的

Answer 2

Jimin 2020-05-07 23:00:24

tsst2方法加的是类级别锁，整个变成串行，不加的话就是普通执行了

Answer 3

爆炸油条 2020-05-07 04:28:56

我遇到了同样问题，test2的循环变量改为1000，test2 添加synchronized 后的输出顺序是正确的，不添加synchronized时的输出是乱序的