Java线程：并发协作-死锁
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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