I am writing a program which will allow the user to create a system of pipes in a text file, which can then be interpreted and executed, with a bunch of processes, and one or more inputs and one output for each process, which may be linked to STDIN, STDOUT, another process, or nowhere. (I'm planning to include possibilities for more than one output for each process, capturing / outputting to STDERR, etc. but I need to fix this version before adding anything.) However, deadlock is occurring for no apparent reason. The relevant code: 
$water = {
map
{
    my $process = $_;
    my @inputs = @ {$processes{$process}[1]};
    $_, {
    prerequisites => [ @inputs ],
    oo_output =>
        sub
        {
        my ($data) = shift;
        my ($pid, @fh, $active);
        @fh = map { $data->get($_) } @inputs;
                push @fh, \*STDIN if ((defined $start) and $start eq $
+process);
                $active = scalar @fh;
        local (*IN, *OUT, $/, $\);
        $/ = 1;
        $\ = '';
        open2 \*OUT, \*IN, $processes{$process}[0];
        select(IN);
        for (;;)
        {
            my $piece = join '', map { (eof $_) ? "\0" : <$_> } @fh;
            (grep { not eof $_ } @fh) ? (print $piece) : (last);
        }
        close (IN);
        return \*OUT;
            } } } keys %processes };

tie %river, 'Data::Flow', $water;
{
    my $output = $river{$final};
    local $/ = undef;
    local $_;
    $_ = <$output>;
    print;
}
exit 0;

[download]
... where the Data::Denter patterns of the variables are approximately: 
# \%processes
%
    <name> => @
        <command>
        @
            <inputs' names, one per element>

# \@pipes
@
    @
        <from>
        <to>

# $start
<which process connects to STDIN>
# $final
<which process connects to STDOUT>
... and the data file: 
process 1stcat perl -spew ..\gismu.text
process 2ndcat perl -spew ..\cmavo.text
process 3rdcat perl -spew
pipe 1stcat 3rdcat
pipe 2ndcat 3rdcat
final 3rdcat
... and a prompt transcript under Win32 (#s are special actions): 
C:\premchai21\perl>perl multipipe.pl -f pipes
#hang #
#kill.#
-p destination: Broken pipe
-p destination: Broken pipe
#hang #
#kill!#
C:\premchai21\perl>
I tried it in the Perl debugger too, but it was rather unhelpful. What is going wrong? Running ActiveState Perl 5.6.0, build 623, on Win98.

In reply to Deadlock occurring, reason unknown by premchai21

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