Java多线程并发环境下的synchronized死锁实例

Java多线程并发环境下的synchronized死锁实例

Java并发多线程环境中，造成死锁的最简单的场景是：多线程中的一个线程T_A持有锁L1并且申请试图获得锁L2；而多线程中另外一个线程T_B持有锁L2并且试图申请获得锁L1。线程的锁申请操作是阻塞的，于是造成线程T_A和线程T_B无法正确获得想要的锁，两个线程被阻塞进入死锁状态。

例如：

public class MainClass {
    private Object lock1 = new Object();

    private Object lock2 = new Object();

    public static void main(String[] args) {
        MainClass mainClass = new MainClass();
        mainClass.demo();
    }

    private void demo() {
        Thread ta = new Thread(new DeadA());
        Thread tb = new Thread(new DeadB());
        ta.start();
        tb.start();
    }

    private class DeadA implements Runnable {
        private String id = "A";

        @Override
        public void run() {
            System.out.println(id + " 申请锁1...");
            synchronized (lock1) {
                System.out.println(id + " 获得锁1");

                System.out.println(id + " 申请锁2...");
                synchronized (lock2) {
                    //A得不到锁2，死锁
                    System.out.println(id + "获得锁2");
                }
            }

            System.out.println(id + " 运行结束");
        }
    }

    private class DeadB implements Runnable {
        private String id = "B";

        @Override
        public void run() {
            System.out.println(id + " 申请锁2...");
            synchronized (lock2) {
                System.out.println(id + " 获得锁2");

                System.out.println(id + " 申请锁1...");
                synchronized (lock1) {
                    //B得不到锁1，死锁
                    System.out.println(id + " 获得锁1");
                }
            }

            System.out.println(id + " 运行结束");
        }
    }
}

输出：

B 申请锁2...
A 申请锁1...
B 获得锁2
A 获得锁1
B 申请锁1...
A 申请锁2...

Java同步机制：synchronized，wait，notify_zhangphil的博客-CSDN博客/** * 假设A，B两个线程同时运行。但A需要某项前置条件必须满足（data数组装满）后才可以正常运转。 这里让B线程去为满足A的条件去干活。 */public class SYN {int[] data = new int[100];final Object lock = new Object();public SYN() {new Thread(new A())https://blog.csdn.net/zhangphil/article/details/43800949

Java线程同步synchronized wait notifyAll_zhangphil的博客-CSDN博客public class Main { public static void main(String[] args) { Main main = new Main(); main.test(); } private void test() { new Thread(new Runnable() { ...https://blog.csdn.net/zhangphil/article/details/96439409