C#•2y 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 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);
            }

22 Replies

ero•2y ago

what is Stopwatch exactly? the methods GetTimestamp and GetElapsedTime don't exist on System.Diagnostics.Stopwatch

Deleted User 07v456ee0OP•2y ago

yeah they do

Deleted User 07v456ee0OP•2y ago

im just using the Stopwatch from system.diagnostics

ero•2y ago

ah, they're static methods 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);

then you literally measured the time from long startTime = Stopwatch.GetTimestamp(); to TimeSpan elapsedTime = Stopwatch.GetElapsedTime(startTime); which is basically non-existent actually, nevermind, not thinking well today it seems are you sure LinearSearch takes that long? and it's not something else? what do you actually want to measure here?

Saber•2y ago

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

ero•2y ago

a normal stopwatch instance would make this easier stopwatches are also inaccurate in general and should not be used to benchmark code

Deleted User 07v456ee0OP•2y ago

im measuring linear search here, and even if i wasn't genItems doesn't take long (i know this from before manual timing) i was using one lol but i had the same issue so I tried this and it didn't work either what should I use instead because I need to measure the amount of time it takes for some data collection

ero•2y ago

can you show more context?

Deleted User 07v456ee0OP•2y ago

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

ero•2y ago

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

Deleted User 07v456ee0OP•2y ago

        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;
        }

its just a simple for loop

ero•2y ago

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

MODiX•2y ago

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

Deleted User 07v456ee0OP•2y ago

okay ill take a look thanks

ero•2y ago

i mean, is the item to find potentially very early in the array? if it's found instantly, then of course it's gonna take no time at all

Saber•2y ago

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

ero•2y ago

(also that)

MODiX•2y ago

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

00:00:00.0011020

00:00:00.0011020

Compile: 548.432ms | Execution: 49.352ms | React with ❌ to remove this embed.

ero•2y ago

that's 1.1ms

Deleted User 07v456ee0OP•2y ago

i tried it on 30k and counted the seconds, it was 3, and the code gave out 0.0278 ms

ero•2y ago

then it isn't LinearSearch that takes that long

Deleted User 07v456ee0OP•2y ago

im gonna try moving the timestamp turns out it was genItems lol, a small change I made made it take a lot longer thanks for the help 👍

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Stopwatch not giving accurate times