How 'bout this:

use strict;
use warnings;
use Win32::Process;
use Win32::IPC 'wait_any';
use Win32;
use threads;
my @progs = (
 'C:\windows\system32\calc.exe',
 'C:\windows\system32\notepad.exe',
);
my @proclist;
my %proctable;

for (@progs) {
  my $ProcessObj;
  Win32::Process::Create($ProcessObj,
                  $_,
                  "",
                  0,
                  NORMAL_PRIORITY_CLASS,
                  ".")|| die ErrorReport();

  $proctable{$ProcessObj->GetProcessID}{progname} = $_;
  print "process created for $_\n";
  push @proclist, $ProcessObj;
};

$| = 1;
sub ErrorReport{
    print Win32::FormatMessage( Win32::GetLastError() );
}

sub wait_procs {
  while (@proclist) {
    my $x = wait_any(@proclist, INFINITE);
    if ($x) {
      my $proc = splice(@proclist, abs($x) - 1, 1);
      my $id = $proc->GetProcessID;
      my $program = $proctable{$id}{progname};
      print "process finished x=$x id=$id program=$program\n";
    }
  }
  print "thread exit\n";
}

my $thr = threads->create('wait_procs');


print "waiting for input\n";
$_ = <>;
print "input is $_\n";

$thr->join;
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