Question

I started to use the new ConcurrentDictionary from .Net4 to implement a simple caching for a threading project.

But I’m wondering what I have to take care of/be careful about when using it?

What have been your experiences using it?

Answer 1

Members are thread-safe, but you shouldn’t expect a sequence of calls to be thread-safe. For example you can’t expect the following to be thread-safe:

if (!dictionary.ContainsKey(key))
{
    // Another thread may have beaten you to it
    dictionary.Add(key, value);
}

Instead, use the new thread-safe API – e.g.
AddOrUpdate (last one wins in the event of a race condition) or GetOrAdd (first one wins in the event of a race condition).