use strict;
use POSIX 'setsid';
use Apache::SubProcess;

my $r = shift;
$r->send_http_header("text/plain");

$SIG{CHLD} = 'IGNORE';
defined (my $kid = fork) or die "Cannot fork: $!\n";
if ($kid) {
    print "Parent $$ has finished, kid's PID: $kid\n";
}
else {
    $r->cleanup_for_exec(); # untie the socket
    chdir '/'                 or die "Can't chdir to /: $!";
    open STDIN, '/dev/null'   or die "Can't read /dev/null: $!";
    open STDOUT, '>/dev/null' or die "Can't write to /dev/null: $!";
    open STDERR, '>/tmp/log'  or die "Can't write to /tmp/log: $!";
    setsid                    or die "Can't start a new session: $!";

    my $oldfh = select STDERR;
    local $| = 1;
    select $oldfh;
    warn "started\n";
    
    # do something time-consuming
    sleep 1, warn "$_\n" for 1..20;
    warn "completed\n";

    CORE::exit(0); # terminate the process
}