对象锁

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public class User implements Serializable{public static final String USER_LOCK = "User_Lock_";/** * 获取对象锁,每个用户在缓存中有一个锁 *  * @param userId *            用户id * @return ReentrantLock 锁 */private static ReentrantLock getLock(long userId) {ReentrantLock lock = (ReentrantLock) Cache.get(USER_LOCK + userId);if (lock == null) {synchronized (User.class) { // 单例，一个用户，一个锁lock = (ReentrantLock) Cache.get(USER_LOCK + userId);if (lock == null) {lock = new ReentrantLock();Cache.set(USER_LOCK + userId, lock);}}}return lock;}/** * 加锁 *  * @param userId */public static void addLock(long userId) {getLock(userId).lock();}/** * 解锁 *  * @param userId */public static void deleteLock(long userId) {ReentrantLock lock = getLock(userId);if (lock == null) {return;}if (lock.isHeldByCurrentThread()) {lock.unlock();}}        /**        * 清除锁缓存        */         public static void cleanCacheLock(String userId) {               ReentrantLock lock = (ReentrantLock) Cache.get(USER_LOCK + userId);               if (lock == null) {                   return;               }               if (lock.isHeldByCurrentThread()) {                   lock.unlock();                }                if (!lock.hasQueuedThreads()) {                   Cache.delete(USER_LOCK + userId);                }        }       public void updateSignWithLock(long userId) {if (userId == 0) {Logger.info("加锁:userId等于0");return ;}User.addLock(userId);  //加锁try {doUser();} finally {User.deleteLock(userId);  //解锁}}}
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