BazB and I had some very interesting discussions on and off, in the chat room, and through MessageBox, now we come to an agreement that, the pipe() function introduced in perlipc would be a good solution to connect IO handlers between processes.

He suggested me to post a reply to complete this thread, and I am doing so now. A piece of sample attached:

use IO::Handle;

use strict;

$| ++;
pipe(PARENT_READER, CHILD_WRITER);
pipe(CHILD_READER, PARENT_WRITER);
PARENT_WRITER->autoflush(1);
CHILD_WRITER->autoflush(1);

my $pid;
if ($pid = fork()) {
    close(CHILD_READER);
    close(CHILD_WRITER);
    my $buffer;
    print PARENT_WRITER 1;
    while (1) {
        sysread(PARENT_READER, $buffer, 100);
        print "parent revd: $buffer, and reply with ", $buffer + 1, "\
+n";
        sleep(1);
        print PARENT_WRITER $buffer + 1;
    }
} else {
    close(PARENT_READER);
    close(PARENT_WRITER);
    my $buffer;
    while (1) {
        sysread(CHILD_READER, $buffer, 1000);
        print "child revd: $buffer, and reply with ", $buffer + 1, "\n
+";
        sleep(1);
        print CHILD_WRITER $buffer + 1;
    }
}
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