ReentrantReadWriteLock 是一个锁对象,他支持读数据锁和写数据锁;
适合的使用场景
1. 多线程环境
2. 并且共同访问同一个资源数据
3. 要求可以共享读数据,同时读
4. 不能同时写数据
注意事项
- 读操作可以多线程同时一起读数据
- 但在写的时候,多个线程只能有一个线程在写,并且写的同时不允许去读数据
使用方式
public static void main(String[] args) {
//创建并发访问的账户
MyCount myCount = new MyCount("95599200901215522", 10000);
//创建一个锁对象
ReadWriteLock lock = new ReentrantReadWriteLock(false);
//创建一个线程池
ExecutorService pool = Executors.newFixedThreadPool(2);
// ExecutorService pool = Executors.newCachedThreadPool();
//创建一些并发访问用户，一个信用卡，存的存，取的取，好热闹啊
User u1 = new User("张三", myCount, -4000, lock, false);
User u2 = new User("张三他爹", myCount, 6000, lock, false);
User u3 = new User("张三他弟", myCount, -8000, lock, false);
User u4 = new User("张三", myCount, 800, lock, false);
User u5 = new User("张三他爹", myCount, 0, lock, true);
//在线程池中执行各个用户的操作,2个线程池大家在用
// u1 和 u2 两个抢一个执行lock
pool.execute(u1);
pool.execute(u2);
pool.execute(u3);
pool.execute(u4);
pool.execute(u5);
//关闭线程池
pool.shutdown();
}
}
class User implements Runnable {
private String name; //用户名
private MyCount myCount; //所要操作的账户
private int iocash; //操作的金额，当然有正负之分了
private ReadWriteLock myLock; //执行操作所需的锁对象
private boolean ischeck; //是否查询
User(String name, MyCount myCount, int iocash, ReadWriteLock myLock, boolean ischeck) {
this.name = name;
this.myCount = myCount;
this.iocash = iocash;
this.myLock = myLock;
this.ischeck = ischeck;
}
public void run() {
if (ischeck) {
//获取读锁
myLock.readLock().lock();
System.out.println("读：" + name + "正在查询" + myCount + "账户，当前金额为" + myCount.getCash());
// 释放读锁
myLock.readLock().unlock();
} else {
//获取写锁: 同一时间只能有一个线程执行操作
myLock.writeLock().lock();
//执行现金业务
System.out.println("写：" + name + "正在操作" + myCount + "账户，金额为" + iocash + "，当前金额为" + myCount.getCash());
myCount.setCash(myCount.getCash() + iocash);
System.out.println("写：" + name + "操作" + myCount + "账户成功，金额为" + iocash + "，当前金额为" + myCount.getCash());
//释放写锁
myLock.writeLock().unlock();
}
}
}
class MyCount {
private String oid; //账号
private int cash; //账户余额
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 +
'}';
}
}
打印结果
写：张三他爹正在操作MyCount{oid='95599200901215522', cash=10000}账户，金额为6000，当前金额为10000
写：张三他爹操作MyCount{oid='95599200901215522', cash=16000}账户成功，金额为6000，当前金额为16000
写：张三正在操作MyCount{oid='95599200901215522', cash=16000}账户，金额为-4000，当前金额为16000
写：张三操作MyCount{oid='95599200901215522', cash=12000}账户成功，金额为-4000，当前金额为12000
写：张三他弟正在操作MyCount{oid='95599200901215522', cash=12000}账户，金额为-8000，当前金额为12000
写：张三他弟操作MyCount{oid='95599200901215522', cash=4000}账户成功，金额为-8000，当前金额为4000
写：张三正在操作MyCount{oid='95599200901215522', cash=4000}账户，金额为800，当前金额为4000
写：张三操作MyCount{oid='95599200901215522', cash=4800}账户成功，金额为800，当前金额为4800
读：张三他爹正在查询MyCount{oid='95599200901215522', cash=4800}账户，当前金额为4800
实际项目使用
public void cluster() {
mClusterTaskLock.writeLock().lock();//加锁避免并发修改数据
try {
// Attempt to cancel the in-flight request.
mClusterTask.cancel(true);
mClusterTask = new ClusterTask();
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
mClusterTask.execute(mMap.getMapStatus().zoom);
} else {
mClusterTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, mMap.getMapStatus().zoom);
}
} finally {
mClusterTaskLock.writeLock().unlock();//用完释放
}
}
读和写一起使用
private Set<? extends Cluster<T>> getClustersInternal(int discreteZoom) {
Set<? extends Cluster<T>> results;
mCacheLock.readLock().lock();
results = mCache.get(discreteZoom);
mCacheLock.readLock().unlock();
if (results == null) {
mCacheLock.writeLock().lock();
results = mCache.get(discreteZoom);
if (results == null) {
results = mAlgorithm.getClusters(discreteZoom);
mCache.put(discreteZoom, results);
}
mCacheLock.writeLock().unlock();
}
return results;
}
