Java多线程问题--ReentrantReardWriteLock类的用法

本文内容部分引自《Java多线程编程核心技术》，感谢作者！！！

代码地址：https://github.com/xianzhixianzhixian/thread.git

ReentrantReardWriteLock类的优势和用法

1、ReentrantLock类中提供了lock.lock()和lock.unlock()来实现获得对象锁和释放对象锁。但是我们可以考虑这样一个问题，当多个线程需要读取而并不需要修改共享变量的数据时，也是一个线程一个线程同步读取的，这样效率就会变低。

2、ReentrantReadWriteLock类提供了读锁和写锁，lock.readLock().lock()、lock.readLock().unlock()、lock.writeLock().lock()和lock.writeLock().unlock()。其中锁与锁之间读读共享、读写互斥、写读互斥、写写互斥，提高了效率。

读写锁用法以及共享互斥情况示例

• 读读共享

Service.java

/**
 * ReentrantReadWriteLock类中读读共享
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:45
 */
public class Service {
    private ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    public void read(){
        try {
            try {
                readWriteLock.readLock().lock();
                System.out.println("获得读锁 "+Thread.currentThread().getName()
                            +" "+System.currentTimeMillis());
                Thread.sleep(10000);
            } finally {
                readWriteLock.readLock().unlock();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

ThreadA.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:48
 */
public class ThreadA extends Thread {
    private Service service;

    public ThreadA(Service service) {
        this.service = service;
    }

    @Override
    public void run() {
        service.read();
    }
}

ThreadB.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:48
 */
public class ThreadB extends Thread {
    private Service service;

    public ThreadB(Service service) {
        this.service = service;
    }

    @Override
    public void run() {
        service.read();
    }
}

Run.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:49
 */
public class Run {
    public static void main(String[] args) {
        Service service = new Service();
        ThreadA threadA = new ThreadA(service);
        threadA.setName("A");
        ThreadB threadB = new ThreadB(service);
        threadB.setName("B");
        threadA.start();
        threadB.start();
    }
}

运行结果：

• 读写互斥和写读互斥

Service.java

/**
 * ReentrantReadWriteLock读写互斥
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:57
 */
public class Service {
    private ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    public void read(){
        try {
            try {
                readWriteLock.readLock().lock();
                System.out.println("获得读锁 "+ Thread.currentThread().getName()
                        +" "+System.currentTimeMillis());
                Thread.sleep(10000);
            } finally {
                readWriteLock.readLock().unlock();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void write(){
        try {
            try {
                readWriteLock.writeLock().lock();
                System.out.println("获得写锁 "+ Thread.currentThread().getName()
                        +" "+System.currentTimeMillis());
                Thread.sleep(10000);
            } finally {
                readWriteLock.writeLock().unlock();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

ThreadA.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:48
 */
public class ThreadA extends Thread {
    private Service service;

    public ThreadA(Service service) {
        this.service = service;
    }

    @Override
    public void run() {
        service.write();
    }
}

ThreadB.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:48
 */
public class ThreadB extends Thread {
    private Service service;

    public ThreadB(Service service) {
        this.service = service;
    }

    @Override
    public void run() {
        service.read();
    }
}

Run.java读写互斥

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 21:00
 */
public class Run {
    public static void main(String[] args) throws Exception {
        Service service = new Service();
        ThreadA threadA = new ThreadA(service); //写锁
        threadA.setName("A");
        ThreadB threadB = new ThreadB(service); //读锁
        threadB.setName("B");
        threadB.start();
        Thread.sleep(100);
        threadA.start();
    }
}

运行结果：

Run.java写读互斥

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 21:00
 */
public class Run {
    public static void main(String[] args) throws Exception {
        Service service = new Service();
        ThreadA threadA = new ThreadA(service); //写锁
        threadA.setName("A");
        ThreadB threadB = new ThreadB(service); //读锁
        threadB.setName("B");
        threadA.start();
        Thread.sleep(100);
        threadB.start();
    }
}

运行结果：

• 写写互斥

Service.java

/**
 * ReentrantReadWriteLock类中写写锁互斥
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:51
 */
public class Service {
    private ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    public void write(){
        try {
            try {
                readWriteLock.writeLock().lock();
                System.out.println("获得写锁 "+ Thread.currentThread().getName()
                            +" "+System.currentTimeMillis());
                Thread.sleep(10000);
            } finally {
                readWriteLock.writeLock().unlock();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

ThreadA.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:48
 */
public class ThreadA extends Thread {
    private Service service;

    public ThreadA(Service service) {
        this.service = service;
    }

    @Override
    public void run() {
        service.write();
    }
}

ThreadB.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:48
 */
public class ThreadB extends Thread {
    private Service service;

    public ThreadB(Service service) {
        this.service = service;
    }

    @Override
    public void run() {
        service.write();
    }
}

Run.java

/**
 * @author: xianzhixianzhixian
 * @date: 2019-01-23 20:54
 */
public class Run {
    public static void main(String[] args) {
        Service service = new Service();
        ThreadA threadA = new ThreadA(service);
        threadA.setName("A");
        ThreadB threadB = new ThreadB(service);
        threadB.setName("B");
        threadA.start();
        threadB.start();
    }
}

运行结果：