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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