C#でParallelを使った画像読み込みのサンプルプログラム。

Program.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;

namespace SamplePleject
{
    class Program
    {
        static void Main(string[] args)
        {
            SingleTask();

            MaltiTask();

            Console.ReadLine();
        }

        public static void SingleTask()
        {
            Console.WriteLine($"SingleTask Start.");

            var path = Path.GetFullPath(@".\img");
            var files = Directory.EnumerateFiles(path);
            List<Bitmap> list = new List<Bitmap>(files.Count());
            var stopWatch = Stopwatch.StartNew();
            foreach (var x in files)
            {
                using (var fs = new FileStream(x, FileMode.Open, FileAccess.Read, FileShare.Read))
                {
                    var sw = Stopwatch.StartNew();
                    Bitmap b = new Bitmap(fs);
                    list.Add(b);
                    Console.WriteLine($"{sw.ElapsedMilliseconds}ms: {new FileInfo(x).Name}");
                }
            }
            Console.WriteLine($"{stopWatch.ElapsedMilliseconds}ms");
            list.Clear();
            Console.WriteLine($"SingleTask End.");
        }

        public static void MaltiTask()
        {
            Console.WriteLine($"MaltiTask Start.");

            var path = Path.GetFullPath(@".\img");
            var files = Directory.EnumerateFiles(path);
            List<Bitmap> list = new List<Bitmap>(files.Count());
            var stopWatch = Stopwatch.StartNew();
            Parallel.ForEach(files, x =>
            {
                using (var fs = new FileStream(x, FileMode.Open, FileAccess.Read, FileShare.Read))
                {
                    var sw = Stopwatch.StartNew();
                    Bitmap b = new Bitmap(fs);
                    list.Add(b);
                    Console.WriteLine($"{sw.ElapsedMilliseconds}ms: {new FileInfo(x).Name}");
                }
            });
            Console.WriteLine($"end. {stopWatch.ElapsedMilliseconds}ms");
            list.Clear();
            Console.WriteLine($"MaltiTask End.");
        }
    }
}