I would need to see exactly what you are trying in order to comment. I created the following script:

#!/usr/bin/perl -w
use strict;
use IO::File;

my $fifo = "fifo";
sysopen(FIFO, $fifo, O_RDONLY) or die "can't read $fifo: $!";
close FIFO;
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I kicked off your script in background, where it hung. When I run this script, the original script (the one you previously posted) exits, indicating that the open completed.