[concurrency-interest] ConcurrentHashMap of singletons

Nader Aeinehchi nader at aeinehchi.com
Tue Oct 4 05:59:04 EDT 2011

As long as you have correctly populated the map(providers) with provider 
objects, this pattern:
1. acts as a singleton
2. is thread safe
3. scales good

You should prefer this pattern rather synchronizing newInstance.

On 10/04/2011 11:01 AM, Mohan Radhakrishnan wrote:
> Hi,
>     private static final Map<String, Provider> providers =
>         new ConcurrentHashMap<String, Provider>();
>     public static Service newInstance(String name) {
>         Provider p = providers.get(name);
>         if (p == null)
>             throw new IllegalArgumentException(
>                 "No provider registered with name: " + name);
>         return p.newService();
>     }
>  I have had a doubt about this type of code in 'Effective Java' that 
> uses a 'ConcurrentHashMap' instead of synchronizing newInstance. This 
> looks like another way of implementing a set of singletons if we 
> extend this pattern by putting a new object if it is null. Are there 
> any problems here ?
> Thanks,
> Mohan
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