Why is ConcurrentBag so slow in .Net (4.0)? Am I doing it wrong?

Question

Before I started a project, I wrote a simple test to compare the performance of ConcurrentBag from (System.Collections.Concurrent) relative to locking & lists. I am extr

Answer 1

You basically have very few concurrent writes and no contention (Parallel.For doesn't necessarily mean many threads). Try parallelizing the writes and you will observe different results:

class Program
{
    private static object list1_lock = new object();
    private const int collSize = 1000;

    static void Main()
    {
        ConcurrentBagTest();
        LockCollTest();
    }

    private static void ConcurrentBagTest()
    {
        var bag1 = new ConcurrentBag();
        var stopWatch = Stopwatch.StartNew();
        Task.WaitAll(Enumerable.Range(1, collSize).Select(x => Task.Factory.StartNew(() =>
        {
            Thread.Sleep(5);
            bag1.Add(x);
        })).ToArray());
        stopWatch.Stop();
        Console.WriteLine("Elapsed Time = {0}", stopWatch.Elapsed.TotalSeconds);
    }

    private static void LockCollTest()
    {
        var lst1 = new List(collSize);
        var stopWatch = Stopwatch.StartNew();
        Task.WaitAll(Enumerable.Range(1, collSize).Select(x => Task.Factory.StartNew(() =>
        {
            lock (list1_lock)
            {
                Thread.Sleep(5);
                lst1.Add(x);
            }
        })).ToArray());
        stopWatch.Stop();
        Console.WriteLine("Elapsed = {0}", stopWatch.Elapsed.TotalSeconds);
    }
}