Where is ConcurrentDictionary in Reactive Extensions .NET 3.5

Question

My questions is simple. After heavy googling I have learned that I can use ConcurrentDictionary in .NET 3.5 projects using Reactive Extensions and System.Threading.dll version from its install directory. First of all there is no System.Threading.dll, there is only System.Reactive.Windows.Threading in Reactive Extensions .NET 3.5 subdirectory. Adding reference to System.Reactive or System.Reactive.Windows.Threading or to any other from the mentioned .NET 3.5 doesn't give me ConcurrentDictionary class nor it gives me System.Collections.Concurrent namespace. I have downloaded older version of Reactive Extensions SDK and I have found what I have been looking for but my question is: does anybody know what happened to the ConcurrentDictionary backport in actual release of Reactive Extensions, does anybody know where it is or why it is missing. I was not able to find a reasonable answer or any answer at all.

Answer 1

We no longer ship the backport of the TPL with Rx for .NET 3.5. If you want to use the TPL and associated innovations in the field of concurrency, start using .NET 4 (or beyond). Rx itself doesn't need TPL functionality, hence there was no strong need for us to carry around the TPL.

There are too many complications with regards to supportability, maintenance, and quality associated with keeping such a backport alive. For instance, performance characteristics of the TPL on older CLR versions has never been tested much beyond the initial CTP of the TPL several years ago.