using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace FileProcessor

{

    public class Program

    {

        const int maxThreads = 16;

​

        public static void Main()

        {

            Task.Run(async () => await ProcessFiles()).GetAwaiter().GetResult();            

        }

​

        public async static Task ProcessFiles()

        {

            var runningTasks = new List<Task>();

​

            var fileQueue = new Queue<string>();

​

            while (fileQueue.Count > 0)

            {

                // queue up files to process;

                while (runningTasks.Count < maxThreads && fileQueue.Count > 0)

                {

                    runningTasks.Add(ProcessFileAsync(fileQueue.Dequeue()));

                }

​

                var completedTask = await Task.WhenAny(runningTasks).ConfigureAwait(false);

                runningTasks.Remove(completedTask);

            }

​

            await Task.WhenAll(runningTasks).ConfigureAwait(false);

        }

​

        public static async Task ProcessFileAsync(string fileName)

        {

            var fileData = await ReadFileAsync(fileName).ConfigureAwait(false);

            var updatedFileData = await Task.Run(() => UpdateFileAsync(fileData)).ConfigureAwait(false);

            await WriteFileAsync(fileName, updatedFileData).ConfigureAwait(false);

        }

​

        private static async Task WriteFileAsync(string fileName, byte[] updatedFileData)

        {

            using (var fs = new System.IO.FileStream(fileName, System.IO.FileMode.Truncate, System.IO.FileAccess.Write, System.IO.FileShare.Write, 16384, true))

            {

                await fs.WriteAsync(updatedFileData, 0, updatedFileData.Length).ConfigureAwait(false);

            }

        }

​

        private static  byte[] UpdateFileAsync(byte[] fileData)

        {

            // do work here;

            return fileData;

        }

​

        private static async Task<byte[]> ReadFileAsync(string fileName)

        {

            byte[] buff = null; 

​

            using (var fs = new System.IO.FileStream(fileName, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.Read, 16384, true))

            {

                buff = new byte[fs.Length];

                await fs.ReadAsync(buff, 0, (int)fs.Length).ConfigureAwait(false);

            }

​

            return buff;

        }

    }

}

​