java笔记--死锁

死锁：

常见情景之一：同步的嵌套 ：（面试的时候可能直接让写）

class Ticket implements Runnable
{
    private int num=100;
    Object obj=new Object();
    boolean flag=true;
    
    public void run(){
        if(flag){
            while(true){
                synchronized(obj){//【这里是拿obj
                    show();       //想进this】
                }
            }
        }
        else{
            while(true){
                this.show();//（这里是拿this
            }
        }
    }
        public synchronized void show(){
            synchronized(obj){//想进obj）
            if(num>0){
                try{
                    Thread.sleep(10);
                }catch(InterruptedException e){
                }
                System.out.println(Thread.currentThread().getName()+"...func..."+num--);
                }   
            }
        }
    }
public class DeadLock {

    public static void main(String[] args) {
        
        Ticket t=new Ticket();
        
        Thread t1=new Thread(t);
        Thread t2=new Thread(t);
        t1.start();
        try{
            Thread.sleep(10);//先暂停主线程
            }catch(InterruptedException e){}
        t.flag=false;
        t2.start();
    }
}

运行：

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("if....lockAAAAAA");
                    synchronized(MyLock.lockb){
                        System.out.println("if.....lockBBBBB");
                }
            }
    }
    else{
        while(true)
            synchronized(MyLock.lockb){
                System.out.println("else...lockBBBB");
                synchronized(MyLock.locka){
                    System.out.println("else.....lockAAAA");
                    }
                }
        }
    }
}
class MyLock{
    public static final Object locka=new Object();
    public static final Object lockb=new Object();
}
class DeadLock
{
    public static void main(String[] args){
        Test a=new Test(true);//因为只有ture和false两个值，
        Test b=new Test(false);//所以这里可以创建两个对象
        
        Thread t1=new Thread(a);
        Thread t2=new Thread(b);
        t1.start();
        t2.start();
    }
}

运行：