#!/usr/bin/perl

use strict;
use warnings;
use IO::BufferedSelect;

my $fh1;
my $fh2;

my $bs = new IO::BufferedSelect($fh1, $fh2);
while(1)
{
    my @canBeRead = $bs->read_line();
    foreach (@canBeRead) 
    { 
        my ($fh, $line) = @$_;
        my $fh_name = ($fh == $fh1 ? "fh1" : "fh2");
        print "fh_name: $line\n";
    }
}
[download]

... This worked for me.

Really?  It doesn't for me — at least not with the file handles being opened to regular text files.

Buffering is only one of the problems here. The deeper issue is that with respect to select, regular disk files are defined to always be readable (even though the operation might block for a few milliseconds until the read head of the disk is positioned). In other words, if the file pointer is at the end of the file, select would still indicate that the file is readable. And because ->getline() reads until the next newline or eof, you could get partial lines (not terminated by a newline).

So, while the following sort of works, it doesn't fulfill the OP's requirement to read entire lines.

#!/usr/bin/perl
use strict;
use warnings;
use IO::Handle;
use IO::Select;

my ($fname1, $fname2) = qw(1.txt 2.txt);
open my $fh1, $fname1 or die $!;
open my $fh2, $fname2 or die $!;

my $slct = IO::Select->new();
$slct->add($fh1, $fh2);

while (1) {
    my @canBeRead = $slct->can_read(); 
    foreach my $fh (@canBeRead) { 
        my $line = $fh->getline();
        if (defined $line) {
            my $fname = $fh == $fh1 ? $fname1 : $fname2;
            print "$fname: $line\n"
        } else {
            sleep 1;  # be nice
        }
    }
}
[download]

It's effectively the same as

use IO::Handle;

my ($fname1, $fname2) = qw(1.txt 2.txt);
open my $fh1, $fname1 or die $!;
open my $fh2, $fname2 or die $!;

while (1) {
    foreach my $fh ($fh1, $fh2) { 
        my $line = $fh->getline();
        if (defined $line) {
            my $fname = $fh == $fh1 ? $fname1 : $fname2;
            print "$fname: $line\n"
        } else {
            sleep 1;  # be nice
        }
    }
}
[download]

Problem is that if you try to read from a file which has no new data in it, then the io->getline() function will get blocked

That's not true. It will return end-of-file. Or are you reading from something other than a plain file?

See File::Tail

The file that I am readnig from is constantly being written to by some other source, so its not a static file. At times getline will block when there is no new data, and at times it won't when there is new data.

At times getline will block when there is no new data

I'll repeat: No, it won't.

$ perl -le'$|=1; for (;;) { print "poke"; sleep 1; }' > file & perl -M
+IO::Handle -e'sleep 3; print while $_ = STDIN->getline; print "exited
+ instead of blocking\n"' < file ; fg
[1] 29483
poke
poke
poke
poke
exited instead of blocking
perl -le'$|=1; for (;;) { print "poke"; sleep 1; }' > file
^C

$ cat file ; rm file
poke
poke
poke
poke
poke
poke
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Options: open a pipe to xtail, use POE::Wheel::FollowTail, roll your own working program/library with select, write and upload a File::Xtail (no, that last link doesn't work).

when initiating the function call to the threaded function, I pass the file descriptors as well,

You shouldn't have to work with file descriptors. Pass the file name to the thread.

This is how I am opening up the file to read, not sure what do I need to do to read the text files as a socket instead, and how that would help.

my $io = new IO::Handle;
open (my $fh, '<', $FILE) or die $!;

if ($io->fdopen(fileno($fh), "r")) {
...
[download]

It's not immediately clear from the docs, but just saying use IO::Handle entitles you to call IO::Handle methods on normal file handles like your already opened $fh.  In other words, your snippet could be simplified as follows:

use IO::Handle;
open (my $fh, '<', $FILE) or die $!;

# then simply call method from IO::Handle
$fh->getline();
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This doesn't answer the question how to make a socket out of a regular file, but I thought it's worth mentioning nevertheless...

Thanks for the feedback, but anyone know a working solution to this problem.

File::Tail won't work with select, so that only leaves one of the options your provided.