Benchmark_ParallelismInFileSystemEnumerations.ps1

#requires -Version 7

# Download and define function `Time-Command` on demand (will prompt).
# To be safe, inspect the source code at the specified URL first.
if (-not (Get-Command -ErrorAction Ignore Time-Command)) {
  $gistUrl = 'https://gist.github.com/mklement0/9e1f13978620b09ab2d15da5535d1b27/raw/Time-Command.ps1'
  if ((Read-Host "`n====`n  OK to download and define benchmark function ``Time-Command```n  from Gist ${gistUrl}?`n=====`n(y/n)?").Trim() -notin 'y', 'yes') { Write-Warning 'Aborted.'; exit 2 }
  Invoke-RestMethod $gistUrl | Invoke-Expression 3>$null
  if (-not ${function:Time-Command}) { exit 2 }
}

Write-Verbose -Verbose 'Preparing benchmarks...'

# In subfolder ./tf, create 200 subfolders with 10 *.txt files each.
$tf = new-item -force -type directory tf
1..200 | % { 
  $f = new-item -force -type directory "$tf/$_" 
  1..10 | % { $null = new-item -force "$f/$_.txt" }
}

Write-Verbose -Verbose 'Running benchmarks...'

$path = $tf.FullName

# Collect the names of all *.txt files in the subfolders.
Time-Command {                  # foreach statement, no parallelism
  $allFileNamesOfInterest =
    foreach ($dir in [System.IO.DirectoryInfo]::new($path).GetDirectories()) {
      $dir.GetFiles('*.txt').Name
    }
},
{                               # ForEach-Object, no parallelism
  $allFileNamesOfInterest =
   [System.IO.DirectoryInfo]::new($path).GetDirectories() | ForEach-Object {
     $_.GetFiles('*.txt').Name
  }
},
{                               # ForEach-Object -Parallel, up to 5 threads by default.
  $allFileNamesOfInterest =
   [System.IO.DirectoryInfo]::new($path).GetDirectories() | ForEach-Object -Parallel {
     $_.GetFiles('*.txt').Name
  }
}

Write-Verbose -Verbose 'Cleaning up...'

Remove-Item -LiteralPath $path -Recurse