23.读写锁ReadWriteLock

ReentrantReadWriteLock

    所谓的读写锁，是访问资源共享共享锁、互斥锁，如果对资源加了写锁，其他线程无法获取写锁与读锁，但是持有写锁的线程，可以对资源

    加读锁；如果一个线程对资源加了读锁，那么其他线程可以继续加读锁。读读共享、读写互斥、写写互斥

package dmeo9;
public class MyAccount {
    private String oid;
    private int cash;
    public  MyAccount(){
    }
    public MyAccount(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;
    }
}
package dmeo9;
import java.util.concurrent.locks.ReadWriteLock;
public class User implements Runnable {
    private String name;//用户名
    private MyAccount myAccount;//操作的账户
    private int ioCash;//操作的金额
    private ReadWriteLock readWriteLock;//读写锁操作锁需要的锁
    private boolean isCheck;//是否操作？
    public User() {
    }
    public User(String name, MyAccount myAccount, int ioCash, ReadWriteLock readWriteLock, boolean isCheck) {
        this.name = name;
        this.myAccount = myAccount;
        this.ioCash = ioCash;
        this.readWriteLock = readWriteLock;
        this.isCheck = isCheck;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public MyAccount getMyAccount() {
        return myAccount;
    }
    public void setMyAccount(MyAccount myAccount) {
        this.myAccount = myAccount;
    }
    public int getIoCash() {
        return ioCash;
    }
    public void setIoCash(int ioCash) {
        this.ioCash = ioCash;
    }
    public ReadWriteLock getReadWriteLock() {
        return readWriteLock;
    }
    public void setReadWriteLock(ReadWriteLock readWriteLock) {
        this.readWriteLock = readWriteLock;
    }
    public boolean isCheck() {
        return isCheck;
    }
    public void setCheck(boolean check) {
        isCheck = check;
    }
    @Override
    public void run() {
        if (isCheck) {
            /*获取读锁*/
            try {
                readWriteLock.readLock().lock();
                System.err.println("\n读：" + getName() + "\t正在read 查询\t" + getMyAccount() + "\t账户，当前金额为：" + myAccount.getCash());
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                /*释放读锁*/
                readWriteLock.readLock().unlock();
            }
        } else {
            /*获取写的锁*/
            try {
                readWriteLock.writeLock().lock();
                System.err.println("写：" + getName() + "\t正在write 操作\t" + getMyAccount() + "账户，当前金额为：" + myAccount.getCash());
                getMyAccount().setCash(getMyAccount().getCash() + getIoCash());
                System.err.println("操作成功：金额为" + getIoCash() + "\t当前金额为：" + getMyAccount().getCash()+"\n\n");
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                /*释放写锁*/
                /**
                 * 一般用lock或者 readwritelock时，需要把
                 unlock方法放在一个 fianlly 块中，因为程序运行的时候可能会
                 出现一些我们人为控制不了的因素，导致锁一直没释放，那其他线程就进不来了.
                 */
                readWriteLock.writeLock().unlock();
            }
        }
    }
}
package dmeo9;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class DemoReadWriteLock {
    public  static  void main(String[] args){
        MyAccount myAccount = new MyAccount("工商银行95599200901215522",160000);
        ReadWriteLock readWriteLock = new ReentrantReadWriteLock(false);
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        User u1 = new User("张三", myAccount, -4000, readWriteLock, false);
        User u2 = new User("小明", myAccount, 6000, readWriteLock, false);
        User u3 = new User("小明", myAccount, -8000, readWriteLock, false);
        User u4 = new User("小明", myAccount, 800, readWriteLock, false);
        User u5 = new User("小明他爹", myAccount, 0, readWriteLock, true);
        executorService.execute(u1);
        executorService.execute(u2);
        executorService.execute(u3);
        executorService.execute(u4);
        executorService.execute(u5);
        /*关闭线程池*/
        executorService.shutdown();
    }
}
输出：
写：张三	正在write 操作	dmeo9.MyAccount@1a8fdcaa账户，当前金额为：160000
操作成功：金额为-4000	当前金额为：156000


写：小明	正在write 操作	dmeo9.MyAccount@1a8fdcaa账户，当前金额为：156000
操作成功：金额为6000	当前金额为：162000


写：小明	正在write 操作	dmeo9.MyAccount@1a8fdcaa账户，当前金额为：162000
操作成功：金额为-8000	当前金额为：154000


写：小明	正在write 操作	dmeo9.MyAccount@1a8fdcaa账户，当前金额为：154000
操作成功：金额为800	当前金额为：154800


读：小明他爹	正在read 查询	dmeo9.MyAccount@1a8fdcaa	账户，当前金额为：154800