I must say I don't understand the problems you had with segfaults. I can't reproduce them, at least not with the piece of code given here.

I wonder though if this:

BEGIN {
    if ($Config{use5005threads}) { debug( "5005 Threads\n" );

        eval 'use Thread qw(yield); use Thread::Queue';
        die $@ if $@;

        $conn = start_connection( 1 );
        $telnetprintqueue = Thread::Queue->new;
        $screenprintqueue = Thread::Queue->new;
        $connectqueue     = Thread::Queue->new;

    } elsif ($Config{useithreads}) { debug( "I-Threads\n" );

        eval 'use threads; use threads::shared; use Thread::Queue';
        die $@ if $@;

        share( $CONNECT );
        share( $PromptType );

        $telnetprintqueue = Thread::Queue->new;
        $screenprintqueue = Thread::Queue->new;
        $conn = start_connection( 2 );

    } else { debug( "No Threads\n" );

        $conn = start_connection( 0 );
    }
}
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actually works or breaks for you. I realize that in general you don't want string eval's, but these string eval's are happening once at compile time from a fixed string. And compile time itself is nothing but a string eval anyway. I guess that's the exception to the rule ;-)

Anyway, my approach feels cleaner to me, avoiding the forest of requires and imports.

Hope this helps.

Liz