Question

I want to put a value returned from a function into ConcurrentHashmap like that

private static ConcurrentHashMap<String, Object> map = new ConcurrentHashMap<String, Object>();

public void process() {
    map.put(key, function());
}

public Object function() {
    return anyObject;
}

May I know the function (e.g. function()) is thread-safe or not?
Please advise if there is any tutorial
Thanks.

Answer 1

call itself in not thread-safe, only put operation atomic.

Instead you can use guava

ConcurrentMap<Key, Graph> graphs = new MapMaker()
   .concurrencyLevel(4)
   .weakKeys()
   .maximumSize(10000)
   .expireAfterWrite(10, TimeUnit.MINUTES)
   .makeComputingMap(
       new Function<Key, Graph>() {
         public Graph apply(Key key) {
           return createExpensiveGraph(key);
         }
       });

Please notice makeComputingMap() call

http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/MapMaker.html