This module is intended for use in operations that can be done in parallel where the number of processes to be forked off should be limited. Typical use is a downloader which will be retrieving hundreds/thousands of files.
The code for a downloader would look something like this:
use LWP::Simple; use Parallel::ForkManager;
...
my @links=( ["http://www.foo.bar/rulez.data","rulez_data.txt"], ["http://new.host/more_data.doc","more_data.doc"], ... );
...
my $pm = Parallel::ForkManager->new(30);
LINKS: foreach my $linkarray (@links) { $pm->start and next LINKS; # do the fork
my ($link, $fn) = @$linkarray; warn "Cannot get $fn from $link" if getstore($link, $fn) != RC_OK; $pm->finish; # do the exit in the child process} $pm->wait_all_children;
First you need to instantiate the ForkManager with the "new" constructor. You must specify the maximum number of processes to be created. If you specify 0, then NO fork will be done; this is good for debugging purposes.
Next, use $pm->start to do the fork. $pm returns 0 for the child process, and child pid for the parent process (see also perlfunc(1p)/fork()). The "and next" skips the internal loop in the parent process. NOTE: $pm->start dies if the fork fails.
$pm->finish terminates the child process (assuming a fork was done in the "start").
NOTE: You cannot use $pm->start if you are already in the child process. If you want to manage another set of subprocesses in the child process, you must instantiate another Parallel::ForkManager object!