For e.g , input file is: (called "a_file")

8

7

6

5

4

3

2

1
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If 3 processes are running in parallel or serially, the final file will be:

1

2

3

4

5
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I wrote:

 

#! /usr/local/bin/perl

 

chomp($pid  = $$);

$LOCK_EXCLUSIVE = 2;

$UNLOCK         = 8;

$fifo             = "ENV{HOME}/a_file";

 

popup($fifo);

 

sub popup

{

        my($fifo) = @_;

        while (! -e "$fifo.lock")

        {

                open (LOCK, "> $fifo.lock") || die "problem opening $f
+ifo\n";

                flock LOCK , $LOCK_EXCLUSIVE;

                print LOCK $pid;

 

                open (FILE, "< $fifo") || die "problem opening $fifo\n
+";

                @lines = <FILE>;

                close(FILE) || warn "update queue file exited $?\n";;

 

                open (FILE, "> $fifo") || die "problem opening $fifo\n
+";

 

                @sorted = sort @lines;

                $pop = shift @sorted;

                print "$hostname is poping $pop\n";

                print FILE "@sorted\n";

 

                close(FILE) || warn "update queue file exited $?\n";;

                close(LOCK) || warn "lock file exited $?\n";;

                $str=`cat $fifo.lock`;

 

                flock LOCK, $UNLOCK;

        }

        if ($pid eq $str)

        {

                print "PID lock file is going to be removed\n" ;

                system("rm $fifo.lock");

 

        }

}
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