Java自学-多线程 死锁

Java 演示多线程死锁

当业务比较复杂，多线程应用里有可能会发生死锁

步骤 1 : 演示死锁

1. 线程1 首先占有对象1，接着试图占有对象2
2. 线程2 首先占有对象2，接着试图占有对象1
3. 线程1 等待线程2释放对象2
4. 与此同时，线程2等待线程1释放对象1
   这样就会。。。一直等待下去

package multiplethread;
   
import charactor.Hero;
    
public class TestThread {
      
    public static void main(String[] args) {
        final Hero ahri = new Hero();
        ahri.name = "九尾妖狐";
        final Hero annie = new Hero();
        annie.name = "安妮";
         
        Thread t1 = new Thread(){
            public void run(){
                //占有九尾妖狐
                synchronized (ahri) {
                    System.out.println("t1 已占有九尾妖狐");
                    try {
                        //停顿1000毫秒，另一个线程有足够的时间占有安妮
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                     
                    System.out.println("t1 试图占有安妮");
                    System.out.println("t1 等待中 。。。。");
                    synchronized (annie) {
                        System.out.println("do something");
                    }
                }  
                 
            }
        };
        t1.start();
        Thread t2 = new Thread(){
            public void run(){
                //占有安妮
                synchronized (annie) {
                    System.out.println("t2 已占有安妮");
                    try {
                         
                        //停顿1000毫秒，另一个线程有足够的时间占有暂用九尾妖狐
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    System.out.println("t2 试图占有九尾妖狐");
                    System.out.println("t2 等待中 。。。。");
                    synchronized (ahri) {
                        System.out.println("do something");
                    }
                }  
                 
            }
        };
        t2.start();
   }
        
}

练习： 死锁

3个同步对象a, b, c
3个线程 t1,t2,t3

故意设计场景，使这3个线程彼此死锁

答案：

package multiplethread;
 
public class TestThread {
       
    public static void main(String[] args) {
        Object a = new Object();
        Object b = new Object();
        Object c = new Object();
 
        Thread t1 =new Thread(){
            public void run(){
                synchronized (a) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    synchronized (b) {
                        synchronized (c) {
                             
                        }
                    }
                }  
            }
        };
        Thread t2 =new Thread(){
            public void run(){
                synchronized (c) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    synchronized (a) {
                        synchronized (b) {
                             
                        }
                    }
                }  
            }
        };
        Thread t3 =new Thread(){
            public void run(){
                synchronized (b) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    synchronized (c) {
                        synchronized (a) {
                             
                        }
                    }
                }  
            }
        };
 
        t1.start();
        t2.start();
        t3.start();
        
   }
         
}