Java: is using synchronized(this) an advisable practice when creating a ConcurrentHashMap object?

Question

I just finished developing a java web service server for a distributed programming course I am attending. One of the requirements was to guarantee multi-thread safety to our project hence I decided to use ConcurrentHashMap objects to store my data. At the end of it all I am left with a question regarding this snippet of code:

    public List<THost> getHList() throws ClusterUnavailable_Exception{

    logger.entering(logger.getName(), "getHList");
    if(hMap==null){
        synchronized(this){
            if(hMap==null){
                hMap=createHMap();
            }
        }
    }
    if(hMap==null){
        ClusterUnavailable cu = new ClusterUnavailable();
        cu.setMessage("Data unavailable.");
        ClusterUnavailable_Exception exc = new ClusterUnavailable_Exception("Data unavailable.", new ClusterUnavailable());
        throw exc;
    }
    else{
        List<THost> hList = new ArrayList<THost>(hMap.values());
        logger.info("Returning list of hosts. Number of hosts returned = "+hList.size());
        logger.exiting(logger.getName(), "getHList");
        return hList;
    }
}

do I have to use the synchronized statement when creating the concurrenthashmap object itself in order to guarantee that the service will not have any unpredictable behavior in a multi-threaded environment?

Answer 1

Don't bother. Eagerly initialize the Map, make the field final, and drop the synchronization until you have proven that it is actually necessary. The cost is minuscule and the "obviously safe and correct" solution will almost never be too slow.

You mentioned this is a class project -- focus on getting the code working. Concurrency is hard enough without inventing additional obstacles that you must then hurdle over.