C# implementation of Map with multicore support
A month or two ago, Joel Spolsky posted a piece on his
blog entitled "Can Your Programming Language Do This?" In a nutshell, he wrote
about how languages with anonymous functions can do things similar to the
notions of map and
(from functional programming) which (in the absence of side effects) can make
it easier to make things "trivially parallelizable".
(This is the point where I stopped writing this blog entry and
paused to reflect on the fact that Microsoft Word drew a red squiggly line
under the word "blog" but not under the word "parallelizable".)
Lots of people responded to the challenge in the title of
Joel's blog entry by writing an implementation of Map and/or Reduce in their
favorite language. Most of these implementations didn't actually contain any
functionality for parallel execution on multiple threads or processes. They
simply demonstrated the language-level features necessary to call Map. In
other words, these implementations were primarily examples of how to do
anonymous functions as arguments. I didn't mind, because my primary machine
had only one core anyway.
Then a few weeks ago I bought a Sony Vaio SZ with a Core 2
Duo processor, and suddenly I was unhappy. A non-parallel implementation of
Map doesn't help me at all! If my primary machine has two cores, I want ways
to use both of them.
(BTW, I really like my new Vaio laptop. Highly
So I wrote a multicore library in C# using the .NET
ThreadPool. It contains several implementations of Map, customized for
(I did not implement Reduce, mostly because I didn't see
much use for it. A parallel Reduce doesn't bring as much benefit as a parallel
If you'd like to see the code, you can download it here (8KB zip). The
main file is multicore.cs. It contains the Map code as well as a bunch of
comments with additional information and URLs for related sources of
information. A Visual Studio 2005 project file is included, as well as a small
suite of NUnit tests.
I'm using this code to speed up some of the solid modeling
operations in my woodworking app. It seems to work pretty well.
- 22 October 2006: Oops! Somebody pointed out that my code
does bad things when the inputs list is empty. Fixed.
- 26 October 2006: Somebody pointed out that Map_AnyTrue
could possibly end up referencing an object after it was disposed. Fixed.