async.ps1

rm -recurse out*
$l = @(1..100)
foreach( $i in $l) {
  mkdir out$i
}
foreach( $i in $l) {
  Start-process -file 'C:\Program Files (x86)\Windows Kits\10\bin\10.0.15063.0\x64\midl.exe' -argumentlist "Sample.idl /out out$i" -RedirectStandardError out$i/err.txt -RedirectStandardOutput out$i/out.txt
}

sync.ps1

rm -recurse out*
$l = @(1..100)
foreach( $i in $l) {
  mkdir out$i
}
foreach( $i in $l) {
  Start-process -file 'C:\Program Files (x86)\Windows Kits\10\bin\10.0.15063.0\x64\midl.exe' -argumentlist "Sample.idl /out out$i" -RedirectStandardError out$i/err.txt -RedirectStandardOutput out$i/out.txt -wait
}