using System;

using System.Collections.Concurrent;

using System.Collections.Generic;

using System.Diagnostics;

​

public class ConcurrentReadDictionary<TKey, TValue>

{

    private Dictionary<TKey, TValue> m_data = new Dictionary<TKey, TValue>();

​

    /// <remarks>

    /// Performs a lock add when requested key does not exist.

    /// </remarks>

    public TValue GetOrAdd(TKey key, TValue value)

    {

        TValue val;

        if (!m_data.TryGetValue(key, out val))

        {

            lock (m_data)

            {

                if (!m_data.TryGetValue(key, out val))

                {

                    m_data[key] = val = value;

                }

            }

        }

​

        return val;

    }

​

    public bool TryGetValue(TKey key, out TValue value) { return m_data.TryGetValue(key, out value); }

}

​

public class Program

{

    public static void Main()

    {

        const int count = 1000;

        const int loopCount = 50000;

​

        var sw = Stopwatch.StartNew();

​

        var concurrentReadDictionary = new ConcurrentReadDictionary<int, int>();

​

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

        {

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

            {

                var k = concurrentReadDictionary.GetOrAdd(j, j);

                Debug.Assert(k == j);

            }

        }

​

        sw.Stop();

​

        Console.WriteLine("ConcurrentReadDictionary for {0:#,##0} writes and {1:#,##0} took {2:#,##0} ms", count, loopCount, sw.ElapsedMilliseconds);

​

        sw.Restart();

​

        var concurrentDictionary = new ConcurrentDictionary<int, int>();

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

        {

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

            {

                var k = concurrentDictionary.GetOrAdd(j, j);

                Debug.Assert(k == j);

            }

        }

​

        sw.Stop();

​

        Console.WriteLine("ConcurrentReadDictionary for {0:#,##0} writes and {1:#,##0} took {2:#,##0} ms", count, loopCount, sw.ElapsedMilliseconds);

    }

}