This version of your code works perfectly (as shown by the output at the end):

#!/usr/bin/perl

#use DBI;
use POSIX;
#use Data::Dumper;
#use Fcntl ':flock';
use strict;
use warnings;
use threads;
use threads::shared;
#use "some IPAM system's package name";

my $host = "1.1.1.1";
my $database = "some_db";
my $user = "some_user";
my $pswd = "some_pswd";

my @threads;

#my $dbh = DBI->connect("DBI:mysql:$database;host=$host", $user, $pswd
+ ,) || die "Could not connect to database: $DBI::errstr";
#$dbh->{'mysql_auto_reconnect'} = 1;

my $sql = qq{
    #a select statement
};

#my $sth = $dbh->prepare($sql);
#$sth->execute();
my $rows = 0;
my @uni_array;

#while(my @request = $sth->fetchrow_array())
for( 1 .. 10 )
{

    #initiated IPAM session


    my @retrieved_objs = ( 1..10 ); #searching for some results

    push @uni_array, @retrieved_objs;

    foreach(@retrieved_objs)
    {
        $rows++;
    }
}

my $number = $rows/10;
my $ceil = ceil($number);

for ( my $count = 1; $count <= $ceil; $count++) {
        my $t = threads->new(\&sub1, $count);
        push(@threads,$t);
}

foreach (@threads) {

        my $num = $_->join();
        print "done with $num\n";
}

print "End of main program\n";

sub sub1 {
        my $num = shift;

        print "started thread $num\n";
        #some code

        sleep($num);
        print "done with thread $num\n";
        return $num;
}
#$sth->finish();
#$dbh->disconnect;
__END__
C:\test>junk28
started thread 1
started thread 2
started thread 3
started thread 4
started thread 5
started thread 6
started thread 7
started thread 8
started thread 9
started thread 10
done with thread 1
done with 1
done with thread 2
done with 2
done with thread 3
done with 3
done with thread 4
done with 4
done with thread 5
done with 5
done with thread 6
done with 6
done with thread 7
done with 7
done with thread 8
done with 8
done with thread 9
done with 9
done with thread 10
done with 10
End of main program
[download]

Which means that the problem lies not with the threading, but with that you've omitted (ie.#some code), and since we are not clairvoyant, we can't really help with that!

(My guess would be that this package: "some IPAM system's package name" is not thread-safe; but it is just a guess.)

Thank you. Now, I know where to debug :)

Just in addition to what BrowserUK said, if you are unable to modify the package causing the problem, then move it from a use statement in the parent thread to a require statement in the child threads - Chances are good this will resolve your issue (assuming you don't need access to the package in the main thread)

Keep in mind that while DBI itself may be thread safe, many DB drivers aren't.