.NET - Dictionary locking vs. ConcurrentDictionary

Question

I couldn't find enough information on ConcurrentDictionary types, so I thought I'd ask about it here.

Currently, I use a Dictionary to hold all users that is accessed constantly by multiple threads (from a thread pool, so no exact amount of threads), and it has synchronized access.

I recently found out that there was a set of thread-safe collections in .NET 4.0, and it seems to be very pleasing. I was wondering, what would be the 'more efficient and easier to manage' option, as i have the option between having a normal Dictionary with synchronized access, or have a ConcurrentDictionary which is already thread-safe.

Reference to .NET 4.0's ConcurrentDictionary

Answer 1

Have you seen the Reactive Extensions for .Net 3.5sp1. According to Jon Skeet, they have backported a bundle of the parallel extensions and concurrent data structures for .Net3.5 sp1.

There is a set of samples for .Net 4 Beta 2, which describes in pretty good detail on how to use them the parallel extensions.

I've just spent the last week testing the ConcurrentDictionary using 32 threads to perform I/O. It seems to work as advertised, which would indicate a tremendous amount of testing has been put into it.

Edit: .NET 4 ConcurrentDictionary and patterns.

Microsoft have released a pdf called Patterns of Paralell Programming. Its reallly worth downloading as it described in really nice details the right patterns to use for .Net 4 Concurrent extensions and the anti patterns to avoid. Here it is.

Answer 2

We've used ConcurrentDictionary for cached collection, that is re-populated every 1 hour and then read by multiple client threads, similar to the solution for the Is this example thread safe? question.

We found, that changing it to ReadOnlyDictionary improved overall performance.