System.Diagnostics.StopWatch elapsed time affected by user changing computer's date/time by Strilanc

Hi Strilanc!

Thanks for bringing up this issue. We are always grateful when customers point towards potential concerns - this helps us ensuring the quality of the .NET Framework and driving the product into the right direction.

Indeed, your analysis is correct. Unfortunately, we cannot address this issue in the immediate future.
However, we have logged it and we will continue thinking about addressing issue in a future release.

I thank you for your time and your contribution.

Greg
(Software Engineer on the .NET Base Class Libraries team)

Thanks for your update. We are rerouting this issue to the appropriate group within the Visual Studio Product Team for triage and resolution. These specialized experts will follow-up with your issue.

Here is test code. Put it inside the main class of a new C# console project.

The code periodically prints out elapsed time as measured by StopWatch, TickCount, and Date.UtcNow. If you change the date of the test machine then the Date measure will be affected and, if the system doesn't have a high resolution timer, so will the StopWatch measure (this is the bug). To make things easier the code prints out if a high resolution timer is found.

        [System.Runtime.InteropServices.DllImport("kernel32.dll")]
        private static extern bool QueryPerformanceCounter(out long freq);

        static void Main(string[] args) {
            long x;
            var hasHighRes = QueryPerformanceCounter(out x);
            Console.WriteLine("High res timer available: " + hasHighRes);
            if (hasHighRes) Console.WriteLine("Issue only appears WITHOUT high res timer");

            var s = System.Diagnostics.Stopwatch.StartNew();
            var starttick = Environment.TickCount;
            var startdate = DateTime.UtcNow;
            while (true) {
                System.Threading.Thread.Sleep(1000);
                unchecked {
                    var dtick = (uint)(Environment.TickCount - starttick);
                    var ddate = DateTime.UtcNow - startdate;
                    Console.WriteLine(String.Format(
                        "stopwatch: {0:0.0}s, tickcount: {1:0.0}s, datedif: {2:0.0}s",
                        s.Elapsed.TotalSeconds,
                        dtick/1000.0,
                        ddate.TotalSeconds));
                }
            }
        }

Thank you for your feedback. In order to efficiently investigate and reproduce this issue, we are requesting additional information outlined below.

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Microsoft Visual Studio Connect Support Team

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