I appreciate that BrowserUK is attempting to help, I'm not knocking that at all (yes-- thank you VERY MUCH BrowserUK). As I just posted in my reply to him-- the Re^2 code is exactly what I'm using to test with:

#! perl -slw
use strict;
use threads;

sub test {
        my $t = shift;

        my $cmd = "c:/windows/system32/sort.exe test$t.dat";
        
        print "Thread $t\n";  # show things are in motion...

        sleep 1;  # kludge to insure all threads are up...

        system "$cmd >sorted$t.dat";

        open F, "<sorted$t.dat" or die $!;
        print "Via system:\n", do{ local $/; <F> };
        close F;
        
        print "Via backticks\n", `$cmd`;

        open F, "$cmd|" or die $!;
        print "Via pipe\n", <F>;
        close F;
}

sub spawnem
{
    my $t1 = async{ \&test(1); };
    my $t2 = async{ \&test(2); };
    my $t3 = async{ \&test(3); };
    my $t4 = async{ \&test(4); };

    $t1->join;
    $t2->join;
    $t3->join;
    $t4->join;
}

&spawnem;
[download]

The test1-4.dat files all contain the same two lines

And I loop the test from the DOS shell with the following .bat script:

LOOP:
perl thread2.pl
goto LOOP
[download]

A typical output I get when it hangs immediately looks like this:

Thread 1

Thread 2

Thread 3

Thread 4

Via system:
hello
world
[download]

where it just sits there and hangs until I ctl-C.

It'd be nice if the problem is a bug in my code, but I had started originally with a larger example and BrowserUK neatly reduced it to a short little thing that worked for him but didn't run multiple threads in parallel. So I modified it so that it would and that's where the code came from. Again, I may have introduced a bug and if so I'd sure like to know where my conception of how threads works is faulty...