What happened? Well, as I mentioned earlier, the Task Parallel Library still uses threads. When you call the Parallel.For method, the .NET Framework starts new threads automatically. I didn’t have problems with the console application because the Console class is thread safe. But in WPF, UI components can be safely accessed only by a dedicated UI thread. Since Parallel.For uses worker threads besides the UI thread, it’s unsafe to manipulate the text block directly in the parallel loop body. If you use, let’s say, Windows Forms, you might have different problems, but problems nonetheless (another exception or even an application crash).
Luckily, WPF provides an API that solves this problem. Most controls have a special Dispatcher object that enables other threads to interact with the UI thread by sending asynchronous messages to it. So our parallel loop should actually look like this:
To make the UI responsive, I am going to use tasks, which is a new concept introduced by the Task Parallel Library. A task represents an asynchronous operation that is often run on a separate thread. The .NET Framework optimizes load balancing and also provides a nice API for managing tasks and making asynchronous calls between them
the TPL provides a different way of handling interactions between threads. It has task schedulers: very useful objects that are responsible for queuing and executing tasks.