synchronized重入后抛出异常，锁释放了吗

Posted 2021-01-25 catchmydream

synchronized用于同步方法或者代码块，使得多个线程在试图并发执行同一个代码块的时候，串行地执行。以达到线程安全的目的。

在多线程的时候是这样的，但是对于单线程，是允许重入的，每重入一次，计数器加1，当退出代码块时，计数器减1。

那正常退出时计数器减1，抛异常时计数器也是减1。那如果两次重入，在内层抛出异常，会释放锁吗？还是只会计数器减1，锁并不会释放？

直接上代码验证：

public class SynchronizedTest1 {
    public static void main(String[] args){
        Test test1 = new Test();
        Thread thread1 = new Thread(test1);
        Thread thread2 = new Thread(test1);
        thread1.start();
        thread2.start();
    }
}
class Test implements Runnable{
    public synchronized void hello() throws Exception{
        System.out.println(Thread.currentThread().getName() + " say hello!!");
        sorry();
        System.out.println(Thread.currentThread().getName() + " helloed");
    }
    public synchronized void sorry() throws Exception{
        System.out.println(Thread.currentThread().getName() + " say sorry!!");
        throw new Exception(Thread.currentThread().getName() + " this is a test!");
    }
    public void run() {
        try {
            hello();
        }catch (Exception e){
            System.out.println(Thread.currentThread().getName() + " exception once");
        }
        try {
            Thread.sleep(10000L);
            System.out.println(Thread.currentThread().getName() + " exit");
        }catch (Exception e){
            System.out.println(Thread.currentThread().getName() + " some exception");
        }
    }
}

Thread-0 say hello!!
Thread-0 say sorry!!
Thread-0 exception once
Thread-1 say hello!!
Thread-1 say sorry!!
Thread-1 exception once
Thread-1 exit
Thread-0 exit

Process finished with exit code 0

　　

从以上运行结果，得出以下结论

结论：synchronized重入之后，抛出异常，跳出synchronized代码块，会释放锁。