gistfile1.cs

using System;
using System.Linq;
using System.Threading.Tasks;
using System.Threading.Tasks.Dataflow;
using System.Numerics;

namespace dataflow
{
    class Message
    {
        public readonly TaskCompletionSource<BigInteger> Completion;
        public Task<BigInteger> Result { get { return Completion.Task; } }

        public readonly BigInteger N;

        public Message(BigInteger n)
        {
            Completion = new TaskCompletionSource<BigInteger>();
            N = n;
        }
    }

    class Program
    {
        static void Main()
        {
            var factorialServer = new ActionBlock<Message>(
                msg => msg.Completion.SetResult(Factorial(msg.N)),
                new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = 4 });

            var fibonacciServer = new ActionBlock<Message>(
                msg => msg.Completion.SetResult(Fibonacci(msg.N)),
                new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = 4 });

            Parallel.ForEach(Enumerable.Range(0, 1000), async i =>
            {
                var factMsg = new Message(i);
                factorialServer.Post(factMsg);

                var fibMsg = new Message(i);
                fibonacciServer.Post(fibMsg);

                Console.WriteLine("{0} -> {1}", i, Tuple.Create(await factMsg.Result, await fibMsg.Result));
            });

            factorialServer.Complete();
            factorialServer.Completion.Wait();
        }

        static BigInteger Factorial(BigInteger n)
        {
            if (n == 0)
                return 1;

            BigInteger value = 1;
            for (BigInteger i = n; i > 0; i--)
            {
                value *= i;
            }

            return value;
        }

        static BigInteger Fibonacci(BigInteger n)
        {
            BigInteger a = 0;
            BigInteger b = 1;

            for (BigInteger i = 0; i < n; i++)
            {
                BigInteger temp = a;
                a = b;
                b = temp + b;
            }

            return a;
        }
    }
}