how to use global vars after forking()

gjoshi has asked for the wisdom of the Perl Monks concerning the following question:

Hello All,

I have one loop and in there i am forking and calling one function which is calling DB handle defined as global variable. Below is the code.

     foreach my $hostname (@host)
     {
         my $thr = fork();
         if($thr) {
             #parent
             push(@childsall, $thr);
             next;
         }
         else
         { 
            connecttohost($hostname);
         }
     }
      foreach my $child_pid (@childsall) {
         my $tmp = waitpid($child_pid, 0);
      }

sub connecttohost
{
   my($hname) = @_;
    my $query = sprintf("SELECT * FROM $DbName WHERE ue_id='$hname');
    my $hash_ref = $::dbh->selectrow_hashref($query);
}
[download]

dbh is defined as global variable. Now my question is how to keep global variable values in case of fork?

thanks --girija

Comment on how to use global vars after forking() Download Code

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Re: how to use global vars after forking() by Corion (Patriarch) on Oct 15, 2015 at 09:43 UTC
Have you read about what DBI has to say about `fork`? Usually, I consider it better to connect to the database only after the call to `fork`, because that way you can be certain that the state of the database library is consistent with the outside world.	[reply] [d/l] [select]
Re: how to use global vars after forking() by nikosv (Deacon) on Oct 15, 2015 at 10:12 UTC
on top of that using DBI with fork is pretty involved,see DBI, fork, and clone.,isn't that a fork-bomb!,although a finite one? (since it runs until the end of the foreach loop)	[reply]
Re: how to use global vars after forking() by shmem (Chancellor) on Oct 15, 2015 at 16:30 UTC
To expand what nikosv wrote: yes, I know this is stripped down example code - but in the child branch, you MUST exit `foreach my $hostname (@host) { my $thr = fork(); if($thr) { #parent push(@childsall, $thr); next; } else { connecttohost($hostname); exit; # <---- here } } foreach my $child_pid (@childsall) { my $tmp = waitpid($child_pid, 0); }` [download] because otherwise each child resumes the loop at its current state, spawning child processes which spawn child processes which spawn child processes which spawn child processes which spawn... perl -le'print map{pack c,($-++?1:13)+ord}split//,ESEL'	[reply] [d/l]
Re^2: how to use global vars after forking() by gjoshi (Sexton) on Oct 16, 2015 at 08:43 UTC
yes I am exiting in child branch. I got the answer. I can use IPC shareable and it works fine	[reply]