发生死锁的原因通常是两个对象的锁相互等待造成的。
以下用一个实例来构造这样的情况：
以下用一个实例来构造这样的情况：
package basic.e_deadlock;
import org.apache.log4j.Logger;
public class TestDeadLock {
public static void main(String[] args) {
DeadlockRisk dead = new DeadlockRisk();
MyThread t1 = new MyThread(dead, 1, 2, "线程1");
MyThread t2 = new MyThread(dead, 3, 4, "线程2");
MyThread t3 = new MyThread(dead, 5, 6, "线程3");
MyThread t4 = new MyThread(dead, 7, 8, "线程4");
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, String threadName) {
this.dead = dead;
this.a = a;
this.b = b;
this.setName(threadName);
}
@Override
public void run() {
dead.read();
dead.write(a, b);
}
}
class DeadlockRisk {
private static Logger logger = Logger.getLogger(DeadlockRisk.class);
private static class Resource {
public int value;
}
private Resource resourceA = new Resource();
private Resource resourceB = new Resource();
public void read() {
logger.debug("===========read begin===========");
synchronized (resourceA) {
logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceA 的锁！");
synchronized (resourceB) {
logger.debug("read():" + Thread.currentThread().getName() + "获取了resourceB 的锁！");
}
}
logger.debug("===========read end=============");
}
public void write(int a, int b) {
logger.debug("===========write begin===========");
synchronized (resourceB) {
logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceB 的锁！");
synchronized (resourceA) {
logger.debug("write():" + Thread.currentThread().getName() + "获取了resourceA 的锁！");
resourceA.value = a;
resourceB.value = b;
}
}
logger.debug("===========write end=============");
}
}
运行结果：
0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin=========== 0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin=========== 0 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin=========== 0 [线程3] DEBUG basic.e_deadlock.DeadlockRisk - ===========read begin=========== 0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceA 的锁！ 0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - read():线程1获取了resourceB 的锁！ 0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end============= 0 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceA 的锁！ 0 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being=========== 1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - read():线程2获取了resourceB 的锁！ 1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========read end============= 1 [线程2] DEBUG basic.e_deadlock.DeadlockRisk - ===========write being=========== 1 [线程1] DEBUG basic.e_deadlock.DeadlockRisk - write():线程1获取了resourceB 的锁！ 1 [线程4] DEBUG basic.e_deadlock.DeadlockRisk - read():线程4获取了resourceA 的锁！
注意：此时线程1在等待resourceB的资源，线程2在等待resourceA的资源。两个线程在相互等待，出现死锁。
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