C# Example: For-loop in parallel execution and the "lock" statement

Hello,

I noticed that a lot of people coding with python are using the parallel- library, whereas I never see people using multithreading in C# or VB.

This is probably because most people don't know how to make use of the current asynchrony tools provided by dot.net's "System.Threading" library.

Here a quick example for a parallel loop:

var result = new List<object>();

System.Threading.Tasks.Parallel.For(0, points.Count, i =>
{

// do something in here

// append whatever you did to the result list like this:

lock(result)

result.Add(whatever)

}

);

the "lock"-keyword prevents simultaneous access to an object,

which is important when in asynchrony mode.

Here is a quick example:

Replies to This Discussion

Permalink Reply by David Rutten on September 14, 2016 at 4:34am

You're better off using a Concurrent collection rather than continually locking on a List<T>. You cannot guarantee that the order of items added to the list is the same as the order in which the loop runs anyway, so using a ConcurrentBag would absolve you from locking responsibilities.

I'm not surprised though that people don't use the C# parallel loops, it's one of the worst notations in the entirety of C# in my opinion. It seems to me that C# is rapidly becoming an odd sock drawer of language paradigm experiments. Unless they get their act together and start deprecating a lot of the old stuff which has been superseded by better alternatives (I'm looking at you ArrayList) we'll end up with a language too big and complicated to learn.

Permalink Reply by David Rutten on September 14, 2016 at 6:47am

Yeah I know, for all my criticism I don't really have a good solution either. I think the main problems with C# today is that core concepts such as immutability and asynchronicity are not part of the bottom-most layer of the language spec. I suspect these shortcomings prevent the compiler programmers from really implementing parallelism on a completely behind-the-scenes level.

I've designed some classes for GH2 that help multi-threading processes that operate on input/output arrays. However it requires implementors to create derived classes, so it's not anywhere near as 'light' as a loop notation.

Permalink Reply by Mateusz Zwierzycki on September 14, 2016 at 7:48am

While I consider concurrent collections, locking, Interlock class and similar quite easy to use, I totally can't get my head around multithreaded "events"... IMHO, what msdn lacks the most is a low/mid - level pseudocode of what all of those functions/classes do. This is certainly one of the most black-boxed topics there..

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