线程死锁 - 黑马程序员技术交流社区

ava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;
}
}
}
}

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