手撕死锁代码

Posted 2023-02-28 Panda_Java

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手撕死锁代码

0. 死锁基础知识
1. 产生死锁代码1
2. 运行结果2
3.产生死锁代码2
4. 运行结果2
5. 避免死锁修改线程2（靠按序申请资源来预防）
6. 运行结果3

0. 死锁基础知识

多个线程同时被阻塞，它们中的⼀个或者全部都在等待某个资源被释放。由于线程被⽆限期地阻塞，因此程序不可能正常终⽌。
如何避免线程死锁?

1. 产生死锁代码1

public class DeadLock 

    public static void main(String[] args) 
        dataSource da = new dataSource();

        //开启线程A，先获取A锁，在获取B锁
        new Thread(() -> 
            try 
                da.getLockA();
             catch (InterruptedException e) 
                e.printStackTrace();
            
        , "线程A").start();
        //开启线程B，先获取B锁，在获取A锁
        new Thread(() -> 
            try 
                da.getLockB();
             catch (InterruptedException e) 
                e.printStackTrace();
            
        , "线程B").start();
    

    //资源类
class dataSource

    private String lockA = "A锁";
    private String lockB = "B锁";

    //getLockA()方法先获取A锁，在获取B锁
    public void getLockA() throws InterruptedException 
        synchronized (lockA)
            System.out.println(Thread.currentThread().getName() + "已经获取" +lockA);
            Thread.sleep(1000); //获取A锁后，睡眠1秒钟，让getLockB()方法获取B锁
            System.out.println(Thread.currentThread().getName() + "尝试获取" +lockB);
            synchronized (lockB)
                System.out.println(Thread.currentThread().getName() + "已经获取" +lockB);
            
        
    
    //getLockB()方法先获取B锁，在获取A锁
    public void getLockB() throws InterruptedException 
        synchronized (lockB)
            System.out.println(Thread.currentThread().getName() + "已经获取" +lockB);
            Thread.sleep(1000);//获取B锁后，睡眠1秒钟，让getLockA()方法获取A锁
            System.out.println(Thread.currentThread().getName() + "尝试获取" +lockA);
            synchronized (lockA)
                System.out.println(Thread.currentThread().getName() + "已经获取" +lockA);

2. 运行结果2

3.产生死锁代码2

public class DeadLockDemo 
    private static Object resource1 = new Object();//资源 1
    private static Object resource2 = new Object();//资源 2
    public static void main(String[] args) 
        new Thread(() -> 
            synchronized (resource1) 
                System.out.println(Thread.currentThread() + "get resource1");
                try 
                    Thread.sleep(1000);
                 catch (InterruptedException e) 
                    e.printStackTrace();
                
                System.out.println(Thread.currentThread() + "waiting get
                        resource2");
                synchronized (resource2) 
                    System.out.println(Thread.currentThread() + "get
                            resource2");
                
            
        , "线程 1").start();
        new Thread(() -> 
            synchronized (resource2) 
                System.out.println(Thread.currentThread() + "get resource2");
                try 
                    Thread.sleep(1000);
                 catch (InterruptedException e) 
                    e.printStackTrace();
                
                System.out.println(Thread.currentThread() + "waiting get
                        resource1");
                synchronized (resource1) 
                    System.out.println(Thread.currentThread() + "get
                            resource1");
                
            
        , "线程 2").start();

4. 运行结果2

5. 避免死锁修改线程2（靠按序申请资源来预防）

new Thread(() -> 
	    synchronized (resource1) 
	         System.out.println(Thread.currentThread() + "get resource1");
	         try 
	             Thread.sleep(1000);
	          catch (InterruptedException e) 
	             e.printStackTrace();
	         
	         System.out.println(Thread.currentThread() + "waiting get
	                 resource2");
	         synchronized (resource2) 
	             System.out.println(Thread.currentThread() + "get
	                     resource2");
	         
	     
	 , "线程 2").start();