You don't need to create a Task[] because WhenAll is set up for varargs. This is fine:

    await Task.WhenAll(p_t, c_t, m_t);

Or you can just await the threads before you need them. They're already started and running at this point.

You also probably want to avoid using Result and just await the completed task for the nicer unwrap syntax. Plus, you don't want to get into the habit of using Result as its a blocking call. Same with WaitAll and WaitAny. Ideally you would never use those. ContinueWith is also not very needed if your style is to use the more plain await syntax. Those methods are more to bridge blocking and async code so an async from the start app might use async extensively and never those methods.

Perhaps search for WhenAny and WhenAll?