PowerShell functions and performance

Question

I've been wondering about the performance impact of functions in PowerShell. Let's say we want to generate 100.000 random numbers using System.Random.

$ranGen = New-Object System.Random

Executing

for ($i = 0; $i -lt 100000; $i++) {
    $void = $ranGen.Next()
}

finishes within 0.19 seconds. I put the call inside a function

Get-RandomNumber {
    param( $ranGen )

    $ranGen.Next()
}

Executing

for ($i = 0; $i -lt 100000; $i++) {
    $void = Get-RandomNumber $ranGen
}

takes about 4 seconds.

Why is there such a huge performance impact?

Is there a way I can use functions and still get the performance I have with the direct call?

Are there better (more performant) ways of code encapsulation in PowerShell?

Answer 1

a function call is expensive. The way to get around that is to put as much as you can IN the function. take a look at the following ...

$ranGen = New-Object System.Random
$RepeatCount = 1e4

'Basic for loop = {0}' -f (Measure-Command -Expression {
    for ($i = 0; $i -lt $RepeatCount; $i++) {
        $Null = $ranGen.Next()
    }
    }).TotalMilliseconds

'Core in function = {0}' -f (Measure-Command -Expression {
function Get-RandNum_Core {
    param ($ranGen)
    $ranGen.Next()
    }

    for ($i = 0; $i -lt $RepeatCount; $i++) {
        $Null = Get-RandNum_Core $ranGen
    }
    }).TotalMilliseconds

'All in function = {0}' -f (Measure-Command -Expression {
    function Get-RandNum_All {
        param ($ranGen)
        for ($i = 0; $i -lt $RepeatCount; $i++) {
            $Null = $ranGen.Next()
            }
        }
    Get-RandNum_All $ranGen
    }).TotalMilliseconds

output ...

Basic for loop = 49.4918
Core in function = 701.5473
All in function = 19.5579

from what i vaguely recall [and can't find again], after a certain number of repeats, the function scriptblock gets JIT-ed ... that seems to be where the speed comes from.