经过测试synchronized并不会立即释放锁

╰半橙微兮° 2022-11-06 01:55 98阅读 0赞

今天在测试进入偏向锁之后调用锁对象的hashCode()会不会升级为重量级锁，结果无意中测试出来了，synchronized进入重量级锁之后，即使临界代码执行完了也并不会立即释放锁

先来看看对象头各个bit的含义

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70]

上代码

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70 1]

public class ObjectHeader { 
    
        public static void main(String[] args) throws InterruptedException { 
            Object monitor = new Object();
            System.out.println("========================没加锁之前=============================================");
            // 设置该JVM参数将偏向锁的延时设置为0
            // -XX:BiasedLockingStartupDelay=0
            synchronized (monitor) { 
                System.out.println(ClassLayout.parseInstance(monitor).toPrintable());
                System.out.println("========================调用hashCode之前=============================================");
                System.out.println(ClassLayout.parseInstance(monitor).toPrintable());
                monitor.hashCode(); // 调用锁对象处于偏向锁状态调用hashCode() 会升级成重量级锁
                System.out.println("========================调用hashCode后=============================================");
                System.out.println(ClassLayout.parseInstance(monitor).toPrintable());
            }
            System.out.println("========================synchronized代码块结束=============================================");
            System.out.println(ClassLayout.parseInstance(monitor).toPrintable());
            Thread.sleep(1000); // 在我电脑上是1000左右会释放锁，根据自己的情况进行赋值
            System.out.println("========================等待一秒之后=============================================");
            System.out.println(ClassLayout.parseInstance(monitor).toPrintable());
    
    
        }
    }

# 分析结果 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70 2]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70 3]

这是我自己测试出来的结果，欢迎大佬来纠正。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70]: /images/20221023/9f0423af01b84f808eb1df116abfb295.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70 1]: /images/20221023/47f9659b02d2443a81216612b0286148.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20210307161913841.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1Z2UxMTIz_size_16_color_FFFFFF_t_70 3]: /images/20221023/bf309bc2c3ca4d4ebb6d0e0ad21dd8ec.png