Parallel iteration in C#?

Question

Is there a way to do foreach style iteration over parallel enumerables in C#? For subscriptable lists, I know one could use a regular for loop iterati

Answer 1

Would this work for you?

public static class Parallel
{
    public static void ForEach(IEnumerable[] sources,
                                  Action action)
    {
        foreach (var enumerable in sources)
        {
            ThreadPool.QueueUserWorkItem(source => {
                foreach (var item in (IEnumerable)source)
                    action(item);
            }, enumerable);
        }
    }
}

// sample usage:
static void Main()
{
    string[] s1 = { "1", "2", "3" };
    string[] s2 = { "4", "5", "6" };
    IEnumerable[] sources = { s1, s2 };
    Parallel.ForEach(sources, s => Console.WriteLine(s));
    Thread.Sleep(0); // allow background threads to work
}

For C# 2.0, you need to convert the lambda expressions above to delegates.

Note: This utility method uses background threads. You may want to modify it to use foreground threads, and probably you'll want to wait till all threads finish. If you do that, I suggest you create sources.Length - 1 threads, and use the current executing thread for the last (or first) source.

(I wish I could include waiting for threads to finish in my code, but I'm sorry that I don't know how to do that yet. I guess you should use a WaitHandle Thread.Join().)