Timing C# code using Timer

Question

Even though it is good to check performance of code in terms of algorithmic analysis and Big-Oh! notation i wanted to see how much it takes for the code to execute in my PC. I had initialized a List to 9999count and removed even elements out from the them. Sadly the timespan to execute this seems to be 0:0:0. Surprised by the result there must be something wrong in the way i time the execution. Could someone help me time the code correct?

        IList<int> source = new List<int>(100);
        for (int i = 0; i < 9999; i++)
        {
            source.Add(i);
        }

        TimeSpan startTime, duration;
        startTime = Process.GetCurrentProcess().Threads[0].UserProcessorTime;

        RemoveEven(ref source);
        duration = Process.GetCurrentProcess().Threads[0].UserProcessorTime.Subtract(startTime);

        Console.WriteLine(duration.Milliseconds);
        Console.Read();

Marc Gravell · Accepted Answer · 2012-05-30 06:33:43Z

7

The most appropriate thing to use there would be Stopwatch - anything involving TimeSpan has nowhere near enough precision for this:

var watch = Stopwatch.StartNew();
// something to time
watch.Stop();
Console.WriteLine(watch.ElapsedMilliseconds);

However, a modern CPU is very fast, and it would not surprise me if it can remove them in that time. Normally, for timing, you need to repeat an operation a large number of times to get a reasonable measurement.

Aside: the ref in RemoveEven(ref source) is almost certainly not needed.

answered May 30, 2012 at 6:33

Marc Gravell

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2 Comments

Deeptechtons Over a year ago

So my code was correct but the tool used for measurement was wrong? So are classes passed always by reference in c#?

Marc Gravell Over a year ago

@Deeptechtons any variable/parameter/field to a class instance is a reference, so you are passing a reference. By adding a ref, you are passing a reference, by-reference - which is only useful if you reassign the list in the method.

David Brabant · Accepted Answer · 2012-05-30 06:42:06Z

4

In .Net 2.0 you can use the Stopwatch class

IList<int> source = new List<int>(100);
for (int i = 0; i < 9999; i++)
{
    source.Add(i);
}

Stopwatch watch = new Stopwatch();

watch.Start();
RemoveEven(ref source);
//watch.ElapsedMilliseconds contains the execution time in ms
watch.Stop()

edited May 30, 2012 at 6:42

answered May 30, 2012 at 6:35

David Brabant

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1 Comment

user57508 Over a year ago

the shorthand of var stopwatch = new Stopwatch(); stopwatch.Start(); is var stopwatch = Stopwatch.StartNew();

Răzvan Flavius Panda · Accepted Answer · 2012-05-30 12:04:22Z

1

Adding to previous answers:

var sw = Stopwatch.StartNew();

// instructions to time

sw.Stop();

sw.ElapsedMilliseconds returns a long and has a resolution of:

1 millisecond = 1000000 nanoseconds

sw.Elapsed.TotalMilliseconds returns a double and has a resolution equal to the inverse of Stopwatch.Frequency. On my PC for example Stopwatch.Frequency has a value of 2939541 ticks per second, that gives sw.Elapsed.TotalMilliseconds a resolution of:

1/2939541 seconds = 3,401891655874165e-7 seconds = 340 nanoseconds

answered May 30, 2012 at 12:04

Răzvan Flavius Panda

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