query on fork in perl

[debraj]

Hi

I am trying out a new thing to me ie. use fork(). Now my requirement
is like this :

I have a file which has quite a few numbers such as :

22,23,34 etc.
Now I have a sub-routine say sub create_page, which when passed the
above numbers does quite a few things and creates html pages in their
name, such as 22.html etc.
So instead of passing one at a time, I wanted to pass it to fork'ed
processes so that they happen all at a time. This is where I am
getting stuck. Can anyone help out please ? basically how to call the
same sub with different parameters and on different processes ? and
how to control them ?

My code :
open LIST , "file";
FORKER: while (<LIST>) {
my $newpid = fork();
if ( not defined $newpid )
{
# if return value of fork() is undef, something went wrong
die "fork didn't work: $!\n";
}
elsif ( $newpid == 0 )
{
# if return value is 0, this is the child process
$parent = $pid; # which has a parent called $pid
$pid = $$; # and which will have a process ID of its very
own
@kids = (); # the child doesn't want this baggage from the
parent
last FORKER; # and we don't want the child making babies
either
}
else
{
# the parent process is returned the PID of the newborn by
fork()
print "$$ spawned $newpid \n";
push @kids, $newpid;
$i= $#kids;
$i ++;
}

}

if ( $parent ) # if I have a parent, i.e. if I'm the child process
{
print "I am process number $pid\n";

&create_page("$kids[$i]");
print "Creating $kids[$i]\n";
exit( 0 );
}
else
{
# parent process needs to preside over the death of its kids
while ( my $kid = shift @kids )
{
print "Parent waiting for $kid to die\n";
my $reaped = waitpid( $kid, 0 );
unless ( $reaped == $kid )
{
print "Something's up: $?\n";
}
}
}

 

[Salvador Fandiño]

Hi

I am trying out a new thing to me ie. use fork(). Now my requirement
is like this :

I have a file which has quite a few numbers such as :

22,23,34 etc.
Now I have a sub-routine say sub create_page, which when passed the
above numbers does quite a few things and creates html pages in their
name, such as 22.html etc.
So instead of passing one at a time, I wanted to pass it to fork'ed
processes so that they happen all at a time. This is where I am
getting stuck. Can anyone help out please ? basically how to call the
same sub with different parameters and on different processes ? and
how to control them ?

My code :
open LIST , "file";
FORKER: while (<LIST>) {
my $newpid = fork();
if ( not defined $newpid )
{
# if return value of fork() is undef, something went wrong
die "fork didn't work: $!\n";
}
elsif ( $newpid == 0 )
{
# if return value is 0, this is the child process
$parent = $pid; # which has a parent called $pid
$pid = $$; # and which will have a process ID of its very
own
@kids = (); # the child doesn't want this baggage from the
parent
last FORKER; # and we don't want the child making babies
either
}
else
{
# the parent process is returned the PID of the newborn by
fork()
print "$$ spawned $newpid \n";
push @kids, $newpid;
$i= $#kids;
$i ++;
}

}

if ( $parent ) # if I have a parent, i.e. if I'm the child process
{
print "I am process number $pid\n";

&create_page("$kids[$i]");
print "Creating $kids[$i]\n";
exit( 0 );
}
else
{
# parent process needs to preside over the death of its kids
while ( my $kid = shift @kids )
{
print "Parent waiting for $kid to die\n";
my $reaped = waitpid( $kid, 0 );
unless ( $reaped == $kid )
{
print "Something's up: $?\n";
}
}
}

ufff!

I advise you to use Parallel::ForkManager or Proc::Queue from
CPAN to limit the number of concurrent processes running:



# limit number of child processes to 6
use Proc::Queue size => 6, qw(run_back);
use POSIX ":sys_wait_h";

sub create_page {...}

while(<>) {
my $number=$_;
chomp $number;

# fork and call create_page sub
run_back {
create_page($number)
};

# read childs
1 while waitpid(-1, WNOHANG)>0;
}

# wait for all childs to exit
1 while wait != -1;


Bye,

- Salva

 

[Greg Bacon]

: I have a file which has quite a few numbers such as :
:
: 22,23,34 etc.
: Now I have a sub-routine say sub create_page, which when passed the
: above numbers does quite a few things and creates html pages in their
: name, such as 22.html etc.
: So instead of passing one at a time, I wanted to pass it to fork'ed
: processes so that they happen all at a time. This is where I am
: getting stuck. Can anyone help out please ? basically how to call the
: same sub with different parameters and on different processes ? and
: how to control them ?

See below:

#! /usr/local/bin/perl

use warnings;
use strict;

use POSIX ":sys_wait_h";

sub do_some_work {
my $param = shift;

open my $fh, ">", "$param.html"
or die "$0: open >$param.html: $!";

print $fh map "$_\n",
"<html>",
"<head><title>Happy $param Page</title></head>",
"<body>",
"<h1>Happy $param Page</h1>",
"</body>",
"</html>";
}

## main
my %kid;

for (qw/ 22 23 24 25 /) {
my $pid = fork;

if (not defined $pid) {
warn "$0: fork (item $_): $!";
next;
}
elsif ($pid == 0) {
# child

do_some_work $_;
exit 0;
}
else {
# parent

$kid{$pid} = 1;
}
}

my $errors = 0;
while (scalar keys %kid > 0) {
my $pid = wait;

if ($pid == -1) {
warn "$0: unreaped: " . join(", " => keys %kid);
exit;
}

warn "$0: unknown kid pid $pid"
unless exists $kid{$pid};

++$errors if $? != 0;

delete $kid{$pid};
}

print "Done.\n";

exit $errors;

Hope this helps,
Greg

 

[Brian McCauley]

I am trying out a new thing to me ie. use fork(). Now my requirement
is like this :

I have a file which has quite a few numbers such as :

22,23,34 etc.
Now I have a sub-routine say sub create_page, which when passed the
above numbers does quite a few things and creates html pages in their
name, such as 22.html etc.
So instead of passing one at a time, I wanted to pass it to fork'ed
processes so that they happen all at a time.

Others have addressed how to do this in Perl but I'm not sure that
anyone has pointed out (the non-Perl issue) that unless you expect the
child procesess to be waiting on non-local resources this is probably
not a sensible thing to be doing.

--
\\ ( )
. _\\__[oo
.__/ \\ /\@
. l___\\
# ll l\\
###LL LL\\