How expensive is the lock statement?

Question

I\'ve been experimenting with multi threading and parallel processing and I needed a counter to do some basic counting and statistic analysis of the speed of the processing.

Answer 1

The cost for a lock in a tight loop, compared to an alternative with no lock, is huge. You can afford to loop many times and still be more efficient than a lock. That is why lock free queues are so efficient.

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

namespace LockPerformanceConsoleApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            var stopwatch = new Stopwatch();
            const int LoopCount = (int) (100 * 1e6);
            int counter = 0;

            for (int repetition = 0; repetition < 5; repetition++)
            {
                stopwatch.Reset();
                stopwatch.Start();
                for (int i = 0; i < LoopCount; i++)
                    lock (stopwatch)
                        counter = i;
                stopwatch.Stop();
                Console.WriteLine("With lock: {0}", stopwatch.ElapsedMilliseconds);

                stopwatch.Reset();
                stopwatch.Start();
                for (int i = 0; i < LoopCount; i++)
                    counter = i;
                stopwatch.Stop();
                Console.WriteLine("Without lock: {0}", stopwatch.ElapsedMilliseconds);
            }

            Console.ReadKey();
        }
    }
}

Output:

With lock: 2013
Without lock: 211
With lock: 2002
Without lock: 210
With lock: 1989
Without lock: 210
With lock: 1987
Without lock: 207
With lock: 1988
Without lock: 208