类的多线程

Question

This is a bit of an interesting question but I wanted to know everyone's thoughts on this design pattern.

public class MyThreadedMap {

     private ConcurrentHashMap<Integer, Object> map;

     ...

     public class Wrapper {
          public Object get(int index){
               return map.get(index);
          }
     }
}

At this point multiple threads will have their own instance of Wrapper and would be accessing the map with wrapper.get(index).

I found that the performance change from having the wrapper and not having the wrapper is just slightly better, that is the wrapper helps a little. When I place synchronized on the get method there is a serious performance hit.

What exactly is happening here? When an inner class is instantiated am I creating a copy of that get method for each instance? Would it be best if I just left the wrapper out since there is no real performance gain?

Answer 1

ConcurrentHashMap has fancy ways of minimizing synchronization overhead. When you synchronize the get method, it imposes normal synchronization overhead, thus the performance hit.

If there is no other code in the Wrapper class, I would just leave it out as it doesn't appear to add anything.