So I've been messing around with this a bit too much over the last few days, and I'd like to understand why this is failing. Corion attempted to provide some insight over CB a few days ago, but his insight did not translate into much insight for me. When I execute the following:

#!/usr/bin/perl -w
use strict;
use IPC::Open3;
use Symbol 'gensym';

my @queue = ("Line 1\nThis is the first line\n",
             "Line 2\nThis is the second line\n",
             "Line 3\nThis is the third line\n",
             );

single_thread(@queue);

sub single_thread {
    open my $oldout, ">&", \*STDOUT or die "Can't dup STDOUT: $!";
    
    for (@_) {
        local *STDOUT;
        open STDOUT, '>', \my $stdout or die "Can't redirect STDOUT: $
+!";

        test($_);

        print $oldout "STDOUT: $stdout\n" if defined $stdout;
        close STDOUT;
    }
}

sub test {
    my $line = shift;

    my $pid = open3(my $wtr, my $rdr, undef, 'cat', '-v');
    print $wtr $line;
    close $wtr;

    my $content=do{local $/;<$rdr>};

    local $\;
    print STDOUT $content;
    
    waitpid( $pid, 0 );
}
[download]

I get the output

Line 1
This is the first line
Line 2
This is the second line
Line 3
This is the third line
[download]

This means that when I do the redirect, it mucks up the capture for some reason. If I change sub test to

sub test_mod {
    my $line = shift;

    my $content = `echo '$line'`;

    local $\;
    print STDOUT $content;
}
[download]

I get the expected

STDOUT: Line 1
This is the first line


STDOUT: Line 2
This is the second line


STDOUT: Line 3
This is the third line
[download]

and as well if I swap sub single_thread to

sub single_thread {
    for my $line (@_) {
        my $pid = open3(my $wtr, my $rdr, undef, 'cat', '-v');
        print $wtr $line;
        close $wtr;

        my $content=do{local $/;<$rdr>};

        local $\;
        print "STDOUT: $content\n";
    }
}
[download]

I get

STDOUT: Line 1
This is the first line

STDOUT: Line 2
This is the second line

STDOUT: Line 3
This is the third line
[download]

Any suggestions, other than don't do that? As the subroutine name implies, this is ultimately intended for a multithreaded environment. Essentially, I would like to wrap a subroutine that runs an external command so that it transparently supports threads while maintaining contiguity between each thread's output. I've had this working with backticks for a while, but now I have to modify it to separate the streams and I just don't understand why a core module would show such strange behavior.

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