并发控制挑战：如何使用Java的synchronized关键字保证线程安全?

原创本是古典何须时尚 2024-10-07 03:57 45阅读 0赞

在Java中，synchronized关键字用于实现线程同步。它可以作用于代码块、方法或对象，来确保同一时间只有一个线程可以访问特定部分的代码。

下面是一个简单的例子，说明如何使用`synchronized`关键字保证线程安全：

```java
// 假设我们有一个共享资源类
public class SharedResource {
    private int count;

// synchronized 关键字用于保护 count 访问
    public synchronized void increment() {
        count++;
    }

public synchronized int getCount() {
        return count;
    }
}

// 线程1：尝试增加 count，如果 count 为0，则将 count 设为1
public class Thread1 extends Thread {
    private SharedResource sharedResource;

public Thread1(SharedResource sharedResource) {
        this.sharedResource = sharedResource;
    }

@Override
    public void run() {
        for (int i = 0; i < 5; i++) {
            try {
                sharedResource.increment();
                System.out.println("Thread1: count incremented " + sharedResource.getCount());
            } catch (Exception e) {
                System.out.println("Thread1: failed to increment count due to exception: " + e.getMessage());
            }
        }
    }
}

// 线程2：尝试获取并打印 count
public class Thread2 extends Thread {
    private SharedResource sharedResource;

public Thread2(SharedResource sharedResource) {
        this.sharedResource = sharedResource;
    }

@Override
    public void run() {
        try {
            System.out.println("Thread2: getting count before increment: " + sharedResource.getCount());
            sharedResource.increment();
            System.out.println("Thread2: after incrementing count, printing: " + sharedResource.getCount());
        } catch (Exception e) {
            System.out.println("Thread2: failed to get count or increment due to exception: " + e.getMessage());
        }
    }
}

// 测试代码
public class Main {
    public static void main(String[] args) {
        SharedResource sharedResource = new SharedResource();

Thread1 thread1 = new Thread1(sharedResource);
        Thread2 thread2 = new Thread2(sharedResource);

// 启动线程
        thread1.start();
        thread2.start();

// 线程执行完成后，共享资源进行清理
        try {
            sharedResource.close();
        } catch (IOException e) {
            System.out.println("Error closing SharedResource: " + e.getMessage());
        }
    }
}
```

在这个例子中，`SharedResource`类有一个共享的整数计数器。两个线程`Thread1`和`Thread2`分别尝试增加计数器和获取并打印当前计数器的值。

通过同步锁`synchronized`，我们可以确保同一时间只有一个线程可以访问特定部分的代码，从而保证了线程安全。