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Asked: 2026-05-10T22:10:27+00:00

public Int64 ReturnDifferenceA() { User[] arrayList; Int64 firstTicks; IList<User> userList; Int64 secondTicks; System.Diagnostics.Stopwatch watch;

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public Int64 ReturnDifferenceA() {   User[] arrayList;   Int64 firstTicks;   IList<User> userList;   Int64 secondTicks;   System.Diagnostics.Stopwatch watch;    userList = Enumerable               .Range(0, 1000)               .Select(currentItem => new User()).ToList();    arrayList = userList.ToArray();    watch = new Stopwatch();   watch.Start();    for (Int32 loopCounter = 0; loopCounter < arrayList.Count(); loopCounter++)   {      DoThings(arrayList[loopCounter]);   }    watch.Stop();   firstTicks = watch.ElapsedTicks;    watch.Reset();   watch.Start();   for (Int32 loopCounter = 0; loopCounter < arrayList.Count(); loopCounter++)   {      DoThings(arrayList[loopCounter]);   }   watch.Stop();   secondTicks = watch.ElapsedTicks;    return firstTicks - secondTicks; }

As you can see, this is really simple. Create a list of users, force to an array, start a watch, loop the list through and call a method, stop watch. Repeat. Finish up by returning the difference from the first run and the second.

Now I’m calling with these:

differenceList = Enumerable                  .Range(0, 50)                  .Select(currentItem => ReturnDifferenceA()).ToList(); average = differenceList.Average();  differenceListA = Enumerable                   .Range(0, 50)                   .Select(currentItem => ReturnDifferenceA()).ToList(); averageA = differenceListA.Average();  differenceListB = Enumerable                   .Range(0, 50)                   .Select(currentItem => ReturnDifferenceA()).ToList(); averageB = differenceListB.Average();

Now the fun part is that all averages are positive by a relatively large amount, ranging from 150k to 300k ticks.

What I don’t get is that I am going through the same list, the same way, with the same method and yet there is such a difference. Is there some kind of caching going on?

Another interesting thing is that if I iterate through the list BEFORE the first stop watch section, the averages are around 5k or so.

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1 Answer

  1. by the way, using IEnumerable.Count() on an Array is hundreds of times slower than Array.Length… Although this doesn’t answer the question at all.

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