understanding thread in perl

Shell Programming and Scripting
1

Hi all,

I am trying to build threads which will go to localhost and list the files in given folder.

#!/usr/bin/perl
use threads;
        my $t1 = threads->new(\&sub1, 1);
        my $t2 = threads->new(\&sub2, 2);
     push(@threads,$t1);
      push(@threads,$t2);
 
foreach (@threads) {
my $num = $_->join
} 
 
sub sub1 {
        print "-----started thread 1-----\n";
        system("ssh localhost ls -l /home/user1");
        print "*****done with thread 1*****\n";
        return 1;
sub sub2 {
        print "-----started thread 2-----\n";
        system("ssh localhost ls -l /home/user2");
        print "*****done with thread 2*****\n";
        return 2;
}

I will be very greatfull if someone can explain me the working of BOLD portion and why are they necessory.
If we remove them, perl will simply exit saying 2 threads started 0 unjoined . and will not list the files.

I am using bash Linux bash shell.

2

push (@threads, $t1) and push (@threads, $t2) ==> This will create thread objects and push its references into array @threads.

join() will give you the return value from a thread. I see that from each thread you're storing the return value into $num, but not making any use of it.

There're few errors in your program. I'm sure that was a typo-error. Here's another version of your program:

#!/usr/bin/perl
use threads;
my $t1 = threads->new(\&sub1, 1);
my $t2 = threads->new(\&sub2, 2);
push(@threads,$t1);
push(@threads,$t2);
 
foreach (@threads) {
    my $num = $_->join();
    print "$num\n";
} 
 
sub sub1 {
        print "-----started thread 1-----\n";
        system("ssh localhost ls -l /home/user1");
        print "*****done with thread 1*****\n";
        return 1;
}
sub sub2 {
        print "-----started thread 2-----\n";
        system("ssh localhost ls -l /home/user2");
        print "*****done with thread 2*****\n";
        return 2;
}
1 Like
3

thanks for your help sir,

    I did this code in linux but now i am trying to run it on sunOS and its giving me error could not find threads.pm in @INC.

    Do I have to install something so that it will run....?
4

You may need to install the threads module.

1 Like
5

This thread module needs perl 5.8 or above. Is there any way i can use threas in perl 5.6.1...???

6

There is ithreads (interpreter threads) for perl 5.6. Check the perl documentation to see if ithreads are used or the older 5.005 implementation is used in your system.

A good option is to upgrade your installation of perl. Or if you (or your task) are not so keen on performance, you may fork out another process.