读者写者问题

读写锁

new ReentrantReadWriteLock()

1. 读读共享
2. 读写互斥
3. 写写互斥

代码

public class ReadWriteLockDemo {
          
   
    static class Service {
          
   
        ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
        Lock readLock = readWriteLock.readLock();
        Lock writeLock = readWriteLock.writeLock();

        public void read() {
          
   
            try {
          
   
                readLock.lock(); //申请获得读锁
                System.out.printf("%s开始获得读锁，开始读取数据的时间%s ;
", Thread.currentThread().getName(), System.currentTimeMillis());
                Thread.sleep(1000);//模拟读数据
            } catch (InterruptedException e) {
          
   
                e.printStackTrace();
            } finally {
          
   
                System.out.printf("%s读取数据完毕的时间%s
", Thread.currentThread().getName(), System.currentTimeMillis());
                readLock.unlock();//释放锁

            }
        }

        public void write() {
          
   
            try {
          
   
                writeLock.lock();//申请获得写锁
                System.out.printf("%s获得写锁，开始修改数据%s ;", Thread.currentThread().getName(), System.currentTimeMillis());
                Thread.sleep(5000);//模拟写数据
            } catch (InterruptedException e) {
          
   
                e.printStackTrace();
            } finally {
          
   
                System.out.printf("%s修改数据完毕时间%s
", Thread.currentThread().getName(), System.currentTimeMillis());
                writeLock.unlock();//释放写锁
            }
        }
    }

    static void readRead(Service service) {
          
   
        System.out.println("读读共享 测试结果：");
        //读读共享
        for (int i = 0; i < 5; i++) {
          
   
            Thread thread = new Thread(() -> service.read());
            thread.setName(String.format("readThread%d", i));
            thread.start(); //定义一个线程读数据
        }
    }

    static void writeWrite(Service service) {
          
   
        System.out.println("写写互斥 测试结果：");

        //写写互斥
        for (int j = 0; j < 5; j++) {
          
   
            Thread thread = new Thread(() -> service.write());
            thread.setName(String.format("readThread%d", j));
            thread.start();//定义一个线程写数据
        }
    }

    static void readWrite(Service service) {
          
   
        System.out.println("读写互斥 测试结果：");
        //读写互斥
        for (int k = 5; k < 10; k++) {
          
   
            Thread thread1 = new Thread(() -> service.read());
            thread1.setName(String.format("readThread%d", k));
            thread1.start(); //定义一个线程读数据
            Thread thread2 = new Thread(() -> service.write());
            thread2.setName(String.format("readThread%d", k));
            thread2.start();//定义一个线程写数据
        }
    }

    public static void main(String[] args) {
          
   
        Service service = new Service();
        //以下三个方法请单独运行
        //读读共享  result:多个读线程读取数据时间戳一致
        readRead(service);
        //写写互斥  result:写线程同时只能运行一个
        readWrite(service);
        //读写互斥  result:读写线程同时只能运行一个读线程或者写线程
        writeWrite(service);
    }
}

部分笔试题实例

该部分面试题/笔试题实例来自 @ 例如如下面试题，以上模板可以解决面试题7；问题3-6解法 见本人前两篇文章

第七题 读者写者问题 这也是一个非常经典的多线程题目，题目大意如下：有一个写者很多读者，多个读者可以同时读文件，但写者在写文件时不允许有读者在读文件，同样有读者读时写者也不能写。 依据本例稍作改动即可