产生死锁的四个条件:占有等待、互斥、循环等待、非剥夺。
Java死锁栗子:
public class Main {
//两把钥匙
static Object key1 = new Object();
static Object key2 = new Object();
public static void method1() {
System.out.println(Thread.currentThread().getName()+" enter method1");
synchronized(key1){
try {
//线程1获取key1后睡眠一段时间,等候线程2获得key2
Thread.sleep(300);
//调用method2(),占有key1状态下申请key2
method2();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("leave method1");
}
public static void method2() {
System.out.println(Thread.currentThread().getName()+" enter method2");
synchronized(key2){
try {
//睡眠时间比线程1稍微长些,目的让线程1申请key2时线程2处于占有key2状态
Thread.sleep(500);
//占有key2状态下申请key1
method1();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("leave method2");
}
public static void main(String[] args){
//启动两个线程分别调用method1()和method2()
Thread t1 = new Thread(new Runnable() {
public void run() {
method1();
}
});
t1.start();
Thread t2 = new Thread(new Runnable() {
public void run() {
method2();
}
});
t2.start();
}
}
运行结果:
Thread-0 enter method1
Thread-1 enter method2
Thread-0 enter method2
Thread-1 enter method1
method1()和method2()方法都没有打印退出,Thread1和Thread2分别占有key1和key2的情况下申请key2和key1。满足产生死锁的四个条件。状态如下图: