Java多线程并发环境下的synchronized死锁实例

红太狼 2023-09-24 01:30 147阅读 0赞

## 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())![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/43800949][Java_synchronized_wait_notify_zhangphil_-CSDN_ _ _A_B_A_data_ _B_A_ _public class SYN _int_ data _ new int_100_final Object lock _ new Object_public SYN_ _new Thread_new A_favicon32.ico_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() \{ ...![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/96439409][Java_synchronized wait notifyAll_zhangphil_-CSDN_public class Main _ public static void main_String_ args_ _ Main main _ new Main_ main.test_ _ private void test_ _ new Thread_new Runnable_ _ ..._favicon32.ico_https_blog.csdn.net_zhangphil_article_details_96439409]

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[Java_synchronized_wait_notify_zhangphil_-CSDN_ _ _A_B_A_data_ _B_A_ _public class SYN _int_ data _ new int_100_final Object lock _ new Object_public SYN_ _new Thread_new A_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_43800949]: https://blog.csdn.net/zhangphil/article/details/43800949
[Java_synchronized wait notifyAll_zhangphil_-CSDN_public class Main _ public static void main_String_ args_ _ Main main _ new Main_ main.test_ _ private void test_ _ new Thread_new Runnable_ _ ..._favicon32.ico_https_blog.csdn.net_zhangphil_article_details_96439409]: https://blog.csdn.net/zhangphil/article/details/96439409