Speed up blocking functions with PLINQ

I have been studying the new PLINQ and Parallel Task Library in .Net 4 looking for various ways to do things that we can’t do in .Net 2.0.  PLINQ is huge, and there are a lot of new ways to do multi threaded programming using .Net 4.  In this article I want to cover a particular problem I have had many times over the years.  How do you speed up multithreaded apps that are bound by blocking functions, or long running I/O operations?

I started looking at this method to speed up some long running file I/O routines deep in the VistaDB engine.  Most of time we are blocked in reads from disk before we can continue working, but usually we have part of the blocks we need.  So we could start working, and then continue when the rest of the blocks are loaded.  Adding that logic is complex and prone to error with traditional threading code.  Fortunately PLINQ has a way to make some of these types of operations very simple. 

Reading multiple websites

For this example I am going to read the first page of 8 websites and then act on that information afterwards.  This is the type of very simple parallel operation that splits up really well.  But these types of long running reads are very similar to what happens in many applications.

Side Note on C# 4.0 In a Nutsell Book

I actually adopted this example from one given in Joseph Albahari’s book C# 4.0 In a Nutshell (he is also the author of the excellent LinqPAD).  Weighing in a 1000 pages is not exactly a Nutshell, but it is a fantastic book for developers who already know C# and just want to go through C# and CLR 4.  The concepts in the book cover older versions of .Net as well, but the juicy parts for me were all the new changes.

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