Java线程-线程池-读写锁

上文使用lock接口以及对象，很好的实现了对竞争资源的访问控制，这种锁不区分读写，成为普通锁。为了提高性能，Java提供了读写锁。在读的地方使用读锁，在写的地方使用写锁。在一定程度上提高了程序的执行效率。
Java中读写锁有个接口java.util.concurrent.locks.ReadWriteLock，也有具体的实现ReentrantReadWriteLock，详细的API可以查看JavaAPI文档。

public class Main {
    public static void main(String args[]){
        //创建并发访问的账户
        MyCount myCount=new MyCount("370911199123345123",10000);
        //创建一个锁对象
        ReadWriteLock readWriteLock=new ReentrantReadWriteLock(false);
        //创建一个线程池
        ExecutorService executorService= Executors.newCachedThreadPool();
        User user1=new User(readWriteLock,"张三",myCount,-2000,false);
        User user2=new User(readWriteLock,"李四",myCount,-500,false);
        User user3=new User(readWriteLock,"王五",myCount,3000,false);
        User user4=new User(readWriteLock,"赵六",myCount,-6000,false);
        User user5=new User(readWriteLock,"陈七",myCount,-500,true);
        executorService.execute(user1);
        executorService.execute(user2);
        executorService.execute(user3);
        executorService.execute(user4);
        executorService.execute(user5);
        //关闭线程池
        executorService.shutdown();
    }

}

/**
 * 信用卡用户
 */
class MyCount {
    private String oid;//账户
    private int cash;//余额
    MyCount(String oid,int cash){
        this.oid=oid;
        this.cash=cash;
    }

    public String getOid() {
        return oid;
    }

    public void setOid(String oid) {
        this.oid = oid;
    }

    public int getCash() {
        return cash;
    }

    public void setCash(int cash) {
        this.cash = cash;
    }

    @Override
    public String toString() {
        return "MyCount{" +
                "oid='" + oid + '\'' +
                ", cash=" + cash +
                '}';
    }
}

/**
 * 信用卡账户，可随意透支
 */
class User implements Runnable {
    private String name;    //用户名
    private MyCount myCount;//账户
    private int cash;       //操作的金额
    private ReadWriteLock myLock;    //执行操作所需要的对象
    private boolean isQuery;//是否查询
    User(ReadWriteLock myLock, String name, MyCount myCount, int cash,boolean isQuery){
        this.myLock=myLock;
        this.name=name;
        this.myCount=myCount;
        this.cash=cash;
        this.isQuery=isQuery;
    }

    @Override
    public void run() {
        if(this.isQuery){
            //获取读锁
            this.myLock.readLock().lock();
            System.out.println("读："+name+"正在查询"+this.myCount+"账户，当前金额为"+this.myCount.getCash());
            //释放读锁
            this.myLock.readLock().unlock();
        }else {
            //获取写锁
            this.myLock.writeLock().lock();
            //执行现金业务
            System.out.println(name+"正在操作"+this.myCount+"账户，金额为"+this.cash+",当前金额为"+this.myCount.getCash());
            this.myCount.setCash(this.myCount.getCash()+this.cash);
            System.out.println(name+"操作"+this.myCount+"账户成功，金额为"+this.cash+",当前金额为"+this.myCount.getCash());
            //释放写锁
            this.myLock.writeLock().unlock();
        }
    }
}