[GitHub] dugenkui03 opened a new issue #2610: 优化 LRUCache读取性能

Mon, 08 Oct 2018 12:31:44 -0700 

dugenkui03 opened a new issue #2610: 优化 LRUCache读取性能
URL: https://github.com/apache/incubator-dubbo/issues/2610
 
 
   
[LRUCache](https://github.com/apache/incubator-dubbo/blob/master/dubbo-common/src/main/java/org/apache/dubbo/common/utils/LRUCache.java)
   
   问题
       查询可以加共享锁，更新时才需要加排他锁。因此可以使用信号量替代排他锁提高查询操作的性能。
   
   思路：
       1. 必须使用公平锁：由AQS和Semaphore源码可知非公平锁在高并发情况下会导致更新操作难以执行；
       2. 
信号量初始值为Integer.MAX_VALUE，读取操作则将状态值减1，更新操作则将状态值减Integer.MAX_VALUE，以此来实现查询操作加共享锁，更新操作加排他锁。
   
   主要修改：
   ```java
   //1. 排他锁ReentrantLock替换成信号来能Semaphore；
   
   //2.size()->super.size()父类方法不需要获取许可，且仅在put类操作中被调用
       @Override
       protected boolean removeEldestEntry(java.util.Map.Entry<K, V> eldest) {
           return super.size() > maxCapacity;
       }
   ```
   
   ##### 参考：
   - 《java并发编程实战》14.5 和 14.6 小节
   - 
[信号量测试](https://github.com/dugenkui03/java-source-code/commit/740ac89a43896337a9b09b82775ebc1947684f1e)
   
   
   
   

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