using System;

using System.Linq;

using System.Collections.Concurrent;

using System.Collections.Generic;

using System.Threading.Tasks;

using System.Diagnostics;

​

public class Program

{

    private const int ITEMS_COUNT = 10;

    private const int MAX_DEGREE_OF_PARALLELISM = 1;

    private static readonly TimeSpan IODuration = TimeSpan.FromMilliseconds(10);

    private static IDictionary<string, string> _database = new ConcurrentDictionary<string, string>();

    public static void Main()

    {

        _database = new ConcurrentDictionary<string, string>();

        var timer = Stopwatch.StartNew();

        Insert();

        timer.Stop();

        ValidateDatabase(_database);

        Console.WriteLine("Sequencial: {0} ms", timer.ElapsedMilliseconds);

        _database = new ConcurrentDictionary<string, string>();

        timer = Stopwatch.StartNew();

        InsertBulkParallel();

        timer.Stop();

        ValidateDatabase(_database);

        Console.WriteLine("Parallel Library: {0} ms", timer.ElapsedMilliseconds);

        _database = new ConcurrentDictionary<string, string>();

        timer = Stopwatch.StartNew();

        InsertBulkAsync();

        timer.Stop();

        ValidateDatabase(_database);

        Console.WriteLine("Async Library: {0} ms", timer.ElapsedMilliseconds);

    }

​

    public static void Insert()

    {

        var list = GenerateItems();

        var count = list.Count();

        for (var i = 0; i < count; i++)

        {

            InsertInDatabaseAsync($"{i}", list.ElementAt(i)).GetAwaiter().GetResult();

        }

    }

​

    public static void InsertBulkParallel()

    {

        var list = GenerateItems();

        var count = list.Count();

        var options = new ParallelOptions{MaxDegreeOfParallelism = MAX_DEGREE_OF_PARALLELISM};

        Parallel.For(0, count, options, (i) =>

        {

            InsertInDatabaseAsync($"{i}", list.ElementAt(i)).GetAwaiter().GetResult();

        });

    }

​

    public static void InsertBulkAsync()

    {

        var list = GenerateItems();

        var count = list.Count();

        ForEachAsync(list, (item, index) => InsertInDatabaseAsync($"{index}", item)).GetAwaiter().GetResult();

    }

​

    private static async Task InsertInDatabaseAsync(string index, string item)

    {

        await Task.Delay(IODuration);

        _database[index] = item;

    }

​

    private static IEnumerable<string> GenerateItems()

    {

        var list = new List<string>();

        for (var i = 0; i < ITEMS_COUNT; i++)

        {

            list.Add($"{{\"id\":\"{i}\" }}");

        }

        return list;

    }

​

    private static void ValidateDatabase(IDictionary<string, string> dict)

    {

        if (dict.Count != ITEMS_COUNT)

        {

            throw new Exception("Items count wrong");

        }

        for(var i = 0; i < dict.Count; i++)

        {

            //Console.WriteLine($"dict[{i}] = {dict[i.ToString()]}");

            if(!dict.ContainsKey($"{i}"))

            {

                throw new Exception("Key not found");

            }

        }

    }

​

    private static async Task ForEachAsync<T>(IEnumerable<T> enumerable, Func<T, int, Task> asyncFunc)

    {

        var itemsCount = enumerable.Count();

        var tasks = new Task[itemsCount];

        int i = 0;

        foreach (var t in enumerable)

        {

            tasks[i] = asyncFunc(t, i);

            i++;

        }

        await Task.WhenAll(tasks);

    }

}