C#•3y ago

Stopwatch not giving accurate times

hey everyone, im using stopwatch to measure total milliseconds, but the timing is way off. for example, when

increment

increment

increment

increment is 50k for this piece of code, i count 30 seconds irl but the console says 0.1105ms, which is not even close to correct

            List<float> uLSexI = new();
            tools.log("Unsorted Linear Search, EXISTING Item", ConsoleColor.Red);
            foreach (int increment in increments)
            {
                tools.log($"Increment {increment}");
                genItems(increment);
                item[] itemsUnsorted = items.ToArray();
                int existingQ = itemsUnsorted[random(0, itemsUnsorted.Length)].quantity;
                long startTime = Stopwatch.GetTimestamp();
                int indexFound = LinearSearch(itemsUnsorted, existingQ);
                TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);
                tools.log($"Increment {increment} complete in {(float)elapsedTime.TotalMilliseconds}ms ({elapsedTime.TotalSeconds}s)");
                uLSexI.Add((float)elapsedTime.TotalMilliseconds);
            }

            List<float> uLSexI = new();
            tools.log("Unsorted Linear Search, EXISTING Item", ConsoleColor.Red);
            foreach (int increment in increments)
            {
                tools.log($"Increment {increment}");
                genItems(increment);
                item[] itemsUnsorted = items.ToArray();
                int existingQ = itemsUnsorted[random(0, itemsUnsorted.Length)].quantity;
                long startTime = Stopwatch.GetTimestamp();
                int indexFound = LinearSearch(itemsUnsorted, existingQ);
                TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);
                tools.log($"Increment {increment} complete in {(float)elapsedTime.TotalMilliseconds}ms ({elapsedTime.TotalSeconds}s)");
                uLSexI.Add((float)elapsedTime.TotalMilliseconds);
            }

            List<float> uLSexI = new();
            tools.log("Unsorted Linear Search, EXISTING Item", ConsoleColor.Red);
            foreach (int increment in increments)
            {
                tools.log($"Increment {increment}");
                genItems(increment);
                item[] itemsUnsorted = items.ToArray();
                int existingQ = itemsUnsorted[random(0, itemsUnsorted.Length)].quantity;
                long startTime = Stopwatch.GetTimestamp();
                int indexFound = LinearSearch(itemsUnsorted, existingQ);
                TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);
                tools.log($"Increment {increment} complete in {(float)elapsedTime.TotalMilliseconds}ms ({elapsedTime.TotalSeconds}s)");
                uLSexI.Add((float)elapsedTime.TotalMilliseconds);
            }

            List<float> uLSexI = new();
            tools.log("Unsorted Linear Search, EXISTING Item", ConsoleColor.Red);
            foreach (int increment in increments)
            {
                tools.log($"Increment {increment}");
                genItems(increment);
                item[] itemsUnsorted = items.ToArray();
                int existingQ = itemsUnsorted[random(0, itemsUnsorted.Length)].quantity;
                long startTime = Stopwatch.GetTimestamp();
                int indexFound = LinearSearch(itemsUnsorted, existingQ);
                TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);
                tools.log($"Increment {increment} complete in {(float)elapsedTime.TotalMilliseconds}ms ({elapsedTime.TotalSeconds}s)");
                uLSexI.Add((float)elapsedTime.TotalMilliseconds);
            }

ero•6/11/23, 5:04 PM

what is StopwatchStopwatch exactly?

ero•6/11/23, 5:04 PM

the methods GetTimestampGetTimestamp and GetElapsedTimeGetElapsedTime don't exist on System.Diagnostics.StopwatchSystem.Diagnostics.Stopwatch

Deleted User 07v456ee0OP•6/11/23, 5:05 PM

yeah they do

Deleted User 07v456ee0OP•6/11/23, 5:06 PM

im just using the Stopwatch from system.diagnostics

ero•6/11/23, 5:06 PM

ah, they're static methods

ero•6/11/23, 5:06 PM

yeah so when you do these 3 lines

long startTime = Stopwatch.GetTimestamp();
int indexFound = LinearSearch(itemsUnsorted, existingQ);
TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);

long startTime = Stopwatch.GetTimestamp();
int indexFound = LinearSearch(itemsUnsorted, existingQ);
TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);

ero•6/11/23, 5:07 PM

then you literally measured the time from long startTime = Stopwatch.GetTimestamp();long startTime = Stopwatch.GetTimestamp(); to TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime);

ero•6/11/23, 5:07 PM

which is basically non-existent

ero•6/11/23, 5:07 PM

actually, nevermind, not thinking well today it seems

ero•6/11/23, 5:08 PM

are you sure LinearSearchLinearSearch takes that long?

ero•6/11/23, 5:08 PM

and it's not something else?

ero•6/11/23, 5:08 PM

what do you actually want to measure here?

Saber•6/11/23, 5:08 PM

if genItemsgenItems is what takes time, the start time should be defined before there

ero•6/11/23, 5:08 PM

a normal stopwatch instance would make this easier

ero•6/11/23, 5:09 PM

stopwatches are also inaccurate in general and should not be used to benchmark code

SSaber if `genItems` is what takes time, the start time should be defined before there

Deleted User 07v456ee0OP•6/11/23, 5:09 PM

im measuring linear search here, and even if i wasn't genItems doesn't take long (i know this from before manual timing)

Eero a normal stopwatch instance would make this easier

Deleted User 07v456ee0OP•6/11/23, 5:09 PM

i was using one lol but i had the same issue so I tried this and it didn't work either

Deleted User 07v456ee0OP•6/11/23, 5:10 PM

what should I use instead because I need to measure the amount of time it takes for some data collection

ero•6/11/23, 5:10 PM

can you show more context?

Deleted User 07v456ee0OP•6/11/23, 5:10 PM

and doing it manually is not possible beacause with a small number of items (less than 1000 for example) its almost instant

ero•6/11/23, 5:10 PM

we can't really tell you why LinearSearchLinearSearch is so fast if we don't know what it looks like

Deleted User 07v456ee0OP•6/11/23, 5:11 PM

        static int LinearSearch(item[] array, int target)
        {
            for (int i = 0; i < array.Length; i++)
            {
                if (array[i].quantity == target)
                {
                    return i;
                }
            }
            return -1;
        }

        static int LinearSearch(item[] array, int target)
        {
            for (int i = 0; i < array.Length; i++)
            {
                if (array[i].quantity == target)
                {
                    return i;
                }
            }
            return -1;
        }

Deleted User 07v456ee0OP•6/11/23, 5:11 PM

its just a simple for loop

ero•6/11/23, 5:11 PM

to benchmark code, you want to use a dedicated library like benchmarkdotnet

ero•6/11/23, 5:11 PM

$benchmark

Eero $benchmark

MODiX•6/11/23, 5:11 PM

Try BenchmarkDotNet if you want a sophisticated library for benchmarking https://github.com/dotnet/BenchmarkDotNet

Deleted User 07v456ee0OP•6/11/23, 5:12 PM

okay ill take a look

Deleted User 07v456ee0OP•6/11/23, 5:12 PM

thanks

DDeleted User 07v456ee0 ```cs static int LinearSearch(item[] array, int target) { ...

ero•6/11/23, 5:13 PM

i mean, is the item to find potentially very early in the array?

ero•6/11/23, 5:13 PM

if it's found instantly, then of course it's gonna take no time at all

Saber•6/11/23, 5:14 PM

even with an array of 50k items, theres no way that method would take very long

ero•6/11/23, 5:14 PM

(also that)

MODiX•6/11/23, 5:15 PM

just_ero#0000

REPL Result: Success

int[] ints = Enumerable.Range(0, 50000).ToArray();
Stopwatch sw = Stopwatch.StartNew();

for (int i = 0; i < ints.Length; i++)
{
  if (i == 49999)
    break;
}

sw.Stop();
sw.Elapsed

int[] ints = Enumerable.Range(0, 50000).ToArray();
Stopwatch sw = Stopwatch.StartNew();

for (int i = 0; i < ints.Length; i++)
{
  if (i == 49999)
    break;
}

sw.Stop();
sw.Elapsed

Result: TimeSpan