Java线程：并发协作-死锁

╰半橙微兮° 2024-02-17 21:15 19阅读 0赞

本文转载至：[http://lavasoft.blog.51cto.com/62575/222074][http_lavasoft.blog.51cto.com_62575_222074]

Java线程：并发协作-死锁  
  
线程发生死锁可能性很小，即使看似可能发生死锁的代码，在运行时发生死锁的可能性也是小之又小。  
  
发生死锁的原因一般是两个对象的锁相互等待造成的。  
  
在《Java线程：线程的同步与锁》一文中，简述死锁的概念与简单例子，但是所给的例子是不完整的，这里给出一个完整的例子。

/** 
    * Java线程：并发协作-死锁 
    * 
    * @author Administrator 2009-11-4 22:06:13 
    */ 
    public class Test { 
            public static void main(String[] args) { 
                    DeadlockRisk dead = new DeadlockRisk(); 
                    MyThread t1 = new MyThread(dead, 1, 2); 
                    MyThread t2 = new MyThread(dead, 3, 4); 
                    MyThread t3 = new MyThread(dead, 5, 6); 
                    MyThread t4 = new MyThread(dead, 7, 8); 
    
                    t1.start(); 
                    t2.start(); 
                    t3.start(); 
                    t4.start(); 
            } 
    
    } 
    
    class MyThread extends Thread { 
            private DeadlockRisk dead; 
            private int a, b; 
    
    
            MyThread(DeadlockRisk dead, int a, int b) { 
                    this.dead = dead; 
                    this.a = a; 
                    this.b = b; 
            } 
    
            @Override 
            public void run() { 
                    dead.read(); 
                    dead.write(a, b); 
            } 
    } 
    
    class DeadlockRisk { 
            private static class Resource { 
                    public int value; 
            } 
    
            private Resource resourceA = new Resource(); 
            private Resource resourceB = new Resource(); 
    
            public int read() { 
                    synchronized (resourceA) { 
                            System.out.println("read():" + Thread.currentThread().getName() + "获取了resourceA的锁！"); 
                            synchronized (resourceB) { 
                                    System.out.println("read():" + Thread.currentThread().getName() + "获取了resourceB的锁！"); 
                                    return resourceB.value + resourceA.value; 
                            } 
                    } 
            } 
    
            public void write(int a, int b) { 
                    synchronized (resourceB) { 
                            System.out.println("write():" + Thread.currentThread().getName() + "获取了resourceA的锁！"); 
                            synchronized (resourceA) { 
                                    System.out.println("write():" + Thread.currentThread().getName() + "获取了resourceB的锁！"); 
                                    resourceA.value = a; 
                                    resourceB.value = b; 
                            } 
                    } 
            } 
    }

下面死锁的情况发生了，真是难得一见啊：

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[http_lavasoft.blog.51cto.com_62575_222074]: http://lavasoft.blog.51cto.com/62575/222074
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