Java 死锁

Posted 2020-10-21 学海无涯

/*
死锁：常见情景之一：同步的嵌套。
*/

class Test implements Runnable
{
    private boolean flag;
    Test(boolean flag)
    {
        this.flag = flag;
    }

    public void run()
    {
        if(flag)
        {
            while(true)
                synchronized(MyLock.locka)
                {
                    System.out.println(Thread.currentThread().getName()+"..if   locka....");
                    synchronized(MyLock.lockb)                {
                        
                        System.out.println(Thread.currentThread().getName()+"..if   lockb....");
                    }
                }
        }
        else
        {
            while(true)            
                synchronized(MyLock.lockb)
                {
                    System.out.println(Thread.currentThread().getName()+"..else  lockb....");
                    synchronized(MyLock.locka)
                    {
                        System.out.println(Thread.currentThread().getName()+"..else   locka....");
                    }
                }
        }
    }
}

class MyLock
{
    public static final Object locka = new Object();
    public static final Object lockb = new Object();
}

class SynFunctionLockDemo 
{
    public static void main(String[] args) 
    {
        Test a = new Test(true);
        Test b = new Test(false);

        Thread t1 = new Thread(a);
        Thread t2 = new Thread(b);
        t1.start();
        t2.start();
    }
}

Output：

Thread-0..if   locka....

Thread-1..else  lockb....