Java多线程并发问题：锁竞争和死锁示例-蒲公英云

Java多线程并发问题：锁竞争和死锁示例

原创怼烎@ 2024-12-11 02:15 87阅读 0赞

在Java多线程编程中，锁竞争（Race Condition）和死锁是常见的并发问题。

锁竞争示例：
```java
// 创建两个线程A和B
class MyRunnable implements Runnable {
private Object lock = new Object();

// 这个方法将会被线程调用
@Override
public void run() {

 try {
     synchronized (lock) {  // 使用同一个锁
         System.out.println("Thread " + Thread.currentThread().getName() + " is executing the critical section.");
         lock.wait();  // 等待锁释放
     }
 } catch (InterruptedException e) {
     e.printStackTrace();
 }

}
}

public class Main {
public static void main(String[] args) {
MyRunnable threadA = new MyRunnable();
MyRunnable threadB = new MyRunnable();

    // 创建并启动两个线程
    Thread threadA1 = new Thread(threadA);
    Thread threadB1 = new Thread(threadB);
    threadA1.start();  // 启动线程A
    threadB1.start();  // 启动线程B
    // 此时，锁竞争的问题可能会出现
    // 如果两个线程同时执行到synchronized (lock) {代码块}
    // 并且都试图获取同一个锁（lock），
    // 那么就可能会导致锁竞争问题。
}

}

2. 死锁示例：
```java
// 创建两个互斥资源，比如两个房间
class Room {
    private Object lock = new Object();
    // 获取房间的方法，需要获取锁才能进入
    public synchronized void enter() {
        System.out.println("Thread " + Thread.currentThread().getName() + " entered the room.");
        lock.notify();  // 取消对房间的锁定，让其他线程有机会进入
    }
}
public class Main {
    public static void main(String[] args) {
        Room room1 = new Room();
        Room room2 = new Room();
        // 创建两个线程A和B，分别尝试获取房间并进入
        Thread threadA1 = new Thread(() -> {
            System.out.println("Thread " + Thread.currentThread().getName() + " started acquiring room 1.");
            try {
                room1.enter();  // 尝试获取房间并进入
                System.out.println("Room 1 successfully entered by Thread " + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }));
        Thread threadB1 = new Thread(() -> {
            System.out.println("Thread " + Thread.currentThread().getName() + " started acquiring room 2.");
            try {
                room2.enter();  // 尝试获取房间并进入
                System.out.println("Room 2 successfully entered by Thread " + Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }));
        // 启动线程A和B
        threadA1.start();
        threadB1.start();
        try {
            // 主线程会等待所有子线程结束后再退出
            System.out.println("Main thread is waiting for all subthreads to finish.");
            Thread.sleep(5000);  // 等待5秒
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}