ConcurrentHashMap/ConcurrentMap/Map.compute

[David Holmes]

On 6/12/2012 7:33 AM, Doug Lea wrote:
> On 12/05/12 16:25, Mike Duigou wrote:
>> The problem is that you can't write an atomic putIfAbsent default
>> method in terms of the existing Map API. Thus far we've only
>> contemplated defaults that can match any atomicity expectations
>> provided by the non-default methods.
>>
>
> Right. The idea is that ALL of these would have the same disclaimer as the
> new lambda-friendly ones I listed:
>
> *
> * <p>The default implementation makes no guarantees about
> * synchronization or atomicity properties of this method. Any
> * class overriding this method must specify its concurrency
> * properties.
> *

Which means that ConcurrentMap has to re-abstract all the new methods as 
their default implementations are invalid for maps that people expect 
atomic operations from.

David
-----


> For CHM and related classes, you need each of the original
> four ConcurrentMap methods, and the four new functional ones
> because without them there's no way to get atomicity
> in these contexts.
> But some people like them for the sake of encapsulating
> common forms under standard names even if not atomic.
> I don't have a strong opinion about it, which is why I asked.
>
> -Doug
>