Producer/consumer based on BlockingCollection with a max number of outstanding tasks

example_loop.cs

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

namespace ExampleLoop
{
    class Program
    {
        const int maxQueuedItems = 10;
        const int maxRunningTasks = 5;

        public static void Main()
        {
            using (var bc = new BlockingCollection<int>(maxQueuedItems))
            {
                Task.WaitAll(Sender(bc), Receiver(bc));
            }

            Console.WriteLine("Done!");
        }

        private static async Task Sender(BlockingCollection<int> collection)
        {
            for (int i = 0; i < 100; ++i)
            {
                collection.Add(i);
                // simulate delay
                await Task.Delay(TimeSpan.FromSeconds(0.1));
            }

            collection.CompleteAdding();
        }

        private static async Task Receiver(BlockingCollection<int> collection)
        {
            using (var semaphore = new SemaphoreSlim(maxRunningTasks))
            {
                while (collection.TryTake(out var item, Timeout.Infinite))
                {
                    await semaphore.WaitAsync();

                    // spin off new task
                    Task.Run(
                        async () =>
                        {
                            try
                            {
                                // simulate long processing
                                await Task.Delay(TimeSpan.FromSeconds(1));
                                Console.WriteLine(item);
                            }
                            finally
                            {
                                semaphore.Release();
                            }
                        });
                }

                for (int i = 0; i < maxRunningTasks; ++i)
                {
                    // wait for all outstanding tasks to finish
                    await semaphore.WaitAsync();
                }
            }
        }
    }
}