Java多線程問題--ReentrantReardWriteLock類的用法

本文內容部分引自《Java多線程編程核心技術》，感謝作者！！！

代碼地址：https://github.com/xianzhixianzhixian/thread.git

ReentrantReardWriteLock類的優勢和用法

1、ReentrantLock類中提供了lock.lock()和lock.unlock()來實現獲得對象鎖和釋放對象鎖。但是我們可以考慮這樣一個問題，當多個線程需要讀取而並不需要修改共享變量的數據時，也是一個線程一個線程同步讀取的，這樣效率就會變低。

2、ReentrantReadWriteLock類提供了讀鎖和寫鎖，lock.readLock().lock()、lock.readLock().unlock()、lock.writeLock().lock()和lock.writeLock().unlock()。其中鎖與鎖之間讀讀共享、讀寫互斥、寫讀互斥、寫寫互斥，提高了效率。

讀寫鎖用法以及共享互斥情況示例

• 讀讀共享

Service.java

/**
 * ReentrantReadWriteLock類中讀讀共享
 * @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("獲得讀鎖 "+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();
    }
}

運行結果：

• 讀寫互斥和寫讀互斥

Service.java

/**
 * ReentrantReadWriteLock讀寫互斥
 * @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("獲得讀鎖 "+ 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("獲得寫鎖 "+ 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讀寫互斥

/**
 * @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); //寫鎖
        threadA.setName("A");
        ThreadB threadB = new ThreadB(service); //讀鎖
        threadB.setName("B");
        threadB.start();
        Thread.sleep(100);
        threadA.start();
    }
}

運行結果：

Run.java寫讀互斥

/**
 * @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); //寫鎖
        threadA.setName("A");
        ThreadB threadB = new ThreadB(service); //讀鎖
        threadB.setName("B");
        threadA.start();
        Thread.sleep(100);
        threadB.start();
    }
}

運行結果：

• 寫寫互斥

Service.java

/**
 * ReentrantReadWriteLock類中寫寫鎖互斥
 * @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("獲得寫鎖 "+ 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();
    }
}

運行結果：