Measure time of execution in F#

Question

Please post code for displaying time in F#. I noticed that you can measure it from F# interactive with #time directive, but I don't know how to execute program from FSI

Thanks

Holleyholli

At the time of writing, this wasn't available, but don't use stopwatch and the like, it's extremely flawed. Instead, use Benchmarkdotnet for proper performance measuring, and a profiler. – Beatup

Answer 1

I would just use the .NET Stopwatch class.

let stopWatch = System.Diagnostics.Stopwatch.StartNew()
...
stopWatch.Stop()
printfn "%f" stopWatch.Elapsed.TotalMilliseconds

Birr

But if you're in FSI (F# Interactive REPL), you get more detailed information (CPU time, Real time, GC info). Adding PrivateEye gives even full profiling info from FSI, no extra programming needed. – Beatup

@Beatup Do you happen to know if PrivateEye is still available somewhere? The website is unfortunately defunct. I even contacted one of the authors, and he told me I should still be able to find the code somewhere, but then contact broke of... :( – Entropy

@sebhofer, I don't know. I only use Benchmarkdotnet nowadays, gives much info, and takes care of warmup time, averages, outliers, graphs etc etc. It's used for improving the runtime itself, it's pretty darn stable. – Beatup

When I use this with AOT in 8.0-preview5, I get Unhandled Exception: System.NotSupportedException: 'Microsoft.FSharp.Core.PrintfImpl+Specializations`3[System.IO.TextWriter,Microsoft.FSharp.Core.Unit,Microsoft.FSharp.Core.Unit].CaptureFinal1[System.Int32](Microsoft.FSharp.Core.PrintfImpl+Step[])' is missing native code. MethodInfo.MakeGenericMethod() is not compatible with AOT compilation. Inspect and fix AOT related warnings that were generated when the app was published. For more information see aka.ms/nativeaot-compatibility – Gridiron

Answer 2

From msdn:

By itself, #time toggles whether to display performance information. When it is enabled, F# Interactive measures real time, CPU time, and garbage collection information for each section of code that is interpreted and executed.

So to test you function you have to open F# interactive console and execute your function in it (one way to do it is to select your function, right click and chose Execute in Interactive) Then make a call to your function in Interactive like that for example:

// define your function first either in interactive console or in your document:

let square x = x * x

// in interactive
#time
square 10
#time

You will see how much of real time and CPU time were spent on computation and a bit of information from garbage collector

Nashville

Answer 3

Check out the timer function in the F Sharp Programming wikibook. It is defined like this:

let duration f = 
    let timer = new System.Diagnostics.Stopwatch()
    timer.Start()
    let returnValue = f()
    printfn "Elapsed Time: %i" timer.ElapsedMilliseconds
    returnValue    

Whilst being used like this:

let sample() = System.Threading.Thread.Sleep(2)

duration ( fun() -> sample() )
// or
duration sample

Provide

they are using DateTime.Now to measure time in their function, that's hardly a replacement for the Stopwatch timer. – Birr

@Birr wiki was updated a while back to use stopwatch. Included here for reference – Nosebleed

Answer 4

You could also create custom computation expression to hide actual measuring logic, e.g.:

timer {
   // your code goes here
}

See more examples here: https://fsharpforfunandprofit.com/posts/computation-expressions-bind/

Veronikaveronike