fork() and batch processing mail (was: Quicker array processing)

Hi, I was thinking of a way to improve the speed of an e-mailing script where a bottleneck has arisen because of serial SMTP sending. I'd like to "parallelize" the processing of the address array into 2-4 parallel processes, each sending via SMTP their parts of the array. How would I split processing of the @email_addresses like this? create 2-4 sub-arrays? fork the sending once the sub-array's are populated? Basically I set the e-mail message var's once (body, subject, from) and then do a foreach loop on an array of e-mail addresses, sending the message sequentially. Looking fwd to some Monk-wisdome

edited: Fri Jun 28 00:17:41 2002 by jeffa - title change

[kvale]

It sounds like you are on the right track. I'd suggest the pre-forked server design as detailed in the Perl Cookbook. Basically, you fork off a process for each mail address until you have hit your desired max number of processes. Then wait for each child to finish and start another process at that time. Repeat until done. That will get the task done as quickly as possible, at some expense in space.
From another program I wrote:

my %children = ();   # keys are current child process IDs
my $children = 0;    # current number of children

# Install signal handlers for children.
$SIG{CHLD} = \&REAPER;
$SIG{INT}  = \&HUNTSMAN;
 
# create a set of children
for (1..$max_connections) {
   my $group = shift @groups;
   bear_child( $group) if defined $group;
   last if @groups == 0;
}
 
# And maintain the population.
MAINTAIN:
while (@groups > 0) {
   sleep;    # wait for a signal (i.e., child's death)
   for (my $i = $children; $i < $max_connections; $i++) {
      my $group = shift @groups;
      bear_child( $group);   # top up the child pool
      last MAINTAIN if @groups == 0;
   }
}
 
# wait for the last of the children to complete scanning
sleep while $children > 0;

# reap any wayward children and exit cleanly
HUNTSMAN();

sub REAPER {
   $SIG{CHLD} = \&REAPER;
   my $pid = wait;
   $children--;
   delete $children{$pid};
   print "reaping child $pid\n";
}
 
# handler for SIGINT and normal exit - kill all the children
 
sub HUNTSMAN {
   local($SIG{CHLD}) = \&REAPER;   # we're going to kill our children
   kill 'INT' => keys %children;
   exit;
}

# spawn subprocesses to search groups
 
sub bear_child {
   my $group = shift;
   my $pid;
   my $sigset;
 
   # block signal for fork
   $sigset = POSIX::SigSet->new(SIGINT);
   sigprocmask( SIG_BLOCK, $sigset)
      or die "Can't block SIGINT for fork: $!\n";
 
   # fork a subprocess
   die "fork: $!" unless defined ($pid = fork);
 
   if ($pid) {
      # Parent records the child's birth and returns.
      sigprocmask( SIG_UNBLOCK, $sigset)
         or die "Can't unblock SIGINT for fork: $!\n";
      $children{$pid} = 1;
      $children++;
      return;
   } else {
      # Child process must *not* return from this subroutine.
      $SIG{INT} = 'DEFAULT';      # make SIGINT kill us as it did befo
+re
      # unblock signals
      sigprocmask( SIG_UNBLOCK, $sigset)
         or die "Can't unblock SIGINT for fork: $!\n";
 
      # open a connection to the news server
      undef $nntp;
      until ($nntp) {
         $nntp = Net::NNTP->new( $news_server, Timeout => 60);
      }
      $nntp->authinfo( $username, $password) if defined $username;
 
      print "child $$ searching $group\n";
 
      # do assigned group
      process_group( $group);
 
      # close connection to news server
      $nntp->quit;
 
      print "child $$ is done processing $group\n";
 
      exit; # make sure sub never returns
   }
}

Replace @groups wth @address, and the NNTP stuff with your own processing. Season to taste.
-Mark

[grep]

Have you looked into POE. Although I have not used it (for anything except little tests) and have only seen a demonstration on it, it looks like a good fit for your problem. You can easily feed you array to several different handlers (that will fork off for you).

The notes on the demo that I saw are at http://tilderoot.com/~tcaine/poe. This should at least give you an idea if you want to use POE



grep

Just me, the boy and these two monks, no questions asked.

[gav^]

I do something similar using Mail::Bulkmail and Parallel::ForkManager, basically:
• Create array of emails for each process you want
• Create a child (using Parallel::ForkManager) to handle each array -- see this node for info
• In each child give Mail::Bulkmail the list and the email you want to send off
Hope this helps...

gav^

[flyboy]

I just got done writing an application that does exactly what you want to do. I will give you this one bit of advice. Don't use a foreach loop, like:
for my $email (@emails){
    #fork();
}

I suggest this:
while (@emails){
    my $email = shift(@emails);
    #fork();
}

It will reduce memory usage. At least over time. I'm sure there is a better way, but it works for me.

To handle the message array processing. I set up @mime_data, @text_data array's. Then in my send code something like this:
for (@mime_data){
    s/PATTERN/$var/g;
    push(@foo,$_);
}
Net::SMTP->data("To: $email",@foo);
So I obviously use Net::SMTP. That is the only module I use, I suggest you do the same unless you want to bloat your code - or you know more than I do. :)