The issue I am facing on Windows is that when I run the slave process with its STDIN stream attached to a pipe and, after writing something, I close the perl side, the slave doesn't get the EOF.

The following program shows the issue:

open my $oldin, '<&', \*STDIN or die $!;

pipe my($r), my ($w) or die $!;
open STDIN, '<&', $r or die $!;

my $pid = system 1, 'perl -ne print';
print "pid: $pid\n";

close STDIN or die $!;
open STDIN, '<&', $oldin;

close $r or die $!;
print {$w} "hello world! ($_)\n" for 0..9;
close $w or die $!;

print "waiting for slave process\n";
waitpid $pid, 0 or die $!
[download]

If you run it you will see that the program stalls waiting for the slave to finish.

I can also reproduce the issue with IPC::Open2 open2:

use IPC::Open2 qw(open2);

my $pid = open2 ">&STDOUT", my($w), 'perl -ne print' or die $!;
print "pid: $pid\n";

print {$w} "hello world! ($_)\n" for 0..9;
close $w or die $!;

print "waiting for slave process\n";
waitpid $pid, 0 or die $!
[download]

On the other hand, when a regular file is used, everything works as expected:

open my $oldin, '<&', \*STDIN or die $!;
open STDIN, '<&', \*DATA or die $!;

my $pid = system 1, 'perl -ne print';
print "pid: $pid\n";

close STDIN or die $!;
open STDIN, '<&', $oldin;

print "waiting for slave process\n";
waitpid $pid, 0 or die $!

__DATA__
hello world! (from DATA)
[download]

my $pid = open my $w, '|-', 'perl -ne print' or die $!;
print "pid: $pid\n";

print {$w} "hello world! ($_)\n" for 0..9;
close $w or die $!;

print "waiting for slave process\n";
waitpid $pid, 0 or die $!
[download]

All that occurs to me is that the slave may be inheriting also the write side of the pipe.