ConcurrentMap.putIfAbsent(Object, Supplier)?

[Philippe Marschall]

Hi

I often find myself writing code like this:
ConcurrentMap map = ...;
Object value = map.get(key);
if (value == null) {
  Object newValue = expensiveComputation();
  Object previous = map.putIfAbsent(key, newValue);
  if (previous != null) {
    value = previous;
  } else {
    value = newValue;
  }
}
return value;

This is quite error prone and tedious. If we had a method:

V putIfAbsent(K key, Supplier<V> Supplier)

it could be replaced with

return map.get(key, () -> expensiveComputation());

It could even be implemented with a default method assuming null values 
aren't allowed which is the same as for the new #getOrDefault default 
method.

Cheers
Philippe