There is no point in using ConcurrentDictionary in one thread or synchronizing access if all is done in a single thread. Of course dictionary will beat ConcrurrentDictionary.
Much depends on the usage pattern and number of threads. Here is a test, that shows that ConcurrentDictionary outperforms dictionary and lock with thread number increase.
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Threading;
namespace ConsoleApp
{
class Program
{
static void Main(string[] args)
{
Run(1, 100000, 10);
Run(10, 100000, 10);
Run(100, 100000, 10);
Run(1000, 100000, 10);
Console.ReadKey();
}
static void Run(int threads, int count, int cycles)
{
Console.WriteLine("");
Console.WriteLine($"Threads: {threads}, items: {count}, cycles:{cycles}");
var semaphore = new SemaphoreSlim(0, threads);
var concurrentDictionary = new ConcurrentDictionary<int, string>();
for (int i = 0; i < threads; i++)
{
Thread t = new Thread(() => Run(concurrentDictionary, count, cycles, semaphore));
t.Start();
}
Thread.Sleep(1000);
var w = Stopwatch.StartNew();
semaphore.Release(threads);
for (int i = 0; i < threads; i++)
semaphore.Wait();
Console.WriteLine($"ConcurrentDictionary: {w.Elapsed}");
var dictionary = new Dictionary<int, string>();
for (int i = 0; i < threads; i++)
{
Thread t = new Thread(() => Run(dictionary, count, cycles, semaphore));
t.Start();
}
Thread.Sleep(1000);
w.Restart();
semaphore.Release(threads);
for (int i = 0; i < threads; i++)
semaphore.Wait();
Console.WriteLine($"Dictionary: {w.Elapsed}");
}
static void Run(ConcurrentDictionary<int, string> dic, int elements, int cycles, SemaphoreSlim semaphore)
{
semaphore.Wait();
try
{
for (int i = 0; i < cycles; i++)
for (int j = 0; j < elements; j++)
{
var x = dic.GetOrAdd(i, x => x.ToString());
}
}
finally
{
semaphore.Release();
}
}
static void Run(Dictionary<int, string> dic, int elements, int cycles, SemaphoreSlim semaphore)
{
semaphore.Wait();
try
{
for (int i = 0; i < cycles; i++)
for (int j = 0; j < elements; j++)
lock (dic)
{
if (!dic.TryGetValue(i, out string value))
dic[i] = i.ToString();
}
}
finally
{
semaphore.Release();
}
}
}
}
Threads: 1, items: 100000, cycles:10
ConcurrentDictionary: 00:00:00.0000499
Dictionary: 00:00:00.0000137
Threads: 10, items: 100000, cycles:10
ConcurrentDictionary: 00:00:00.0497413
Dictionary: 00:00:00.2638265
Threads: 100, items: 100000, cycles:10
ConcurrentDictionary: 00:00:00.2408781
Dictionary: 00:00:02.2257736
Threads: 1000, items: 100000, cycles:10
ConcurrentDictionary: 00:00:01.8196668
Dictionary: 00:00:25.5717232
