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#!/usr/bin/perl
#
use POSIX qw(:signal_h :sys_wait_h);

$SIG{CHLD} = \&handler;

# hold SIGCHLD here
my $sigset = POSIX::SigSet->new;
my $blockset = POSIX::SigSet->new(SIGCHLD);
sigprocmask(SIG_BLOCK, $blockset, $sigset) || die "ERROR: could not block SIGCHLD: $!\n";

my $pid = fork();

if(! defined($pid)) { # failed fork()
	die "ERROR: fork() failed: $!\n";
} elsif($pid == 0) {	# child
	# do stuff 
	exit(0);
}

# parent
print STDERR "DEBUG: in parent after first fork(), pid == $pid\n" if $debug;

# release SIGCHLD here
sigprocmask(SIG_SETMASK, $sigset) || 
	die "ERROR: could not restore SIGCHLD signal: $!\n";


exit 0;

sub handler {
	my $signame = shift;
	my $pid; 

	print STDERR "DEBUG: received SIG$signame\n" if $debug;

	if($signame eq "CHLD") {
		while(($pid = waitpid(-1, &WNOHANG)) > 0) {
			# do cleanup stuff
		}
	} # might want to handle sigTERM and shutdown children here
	  # don't forget to waitpid() on any children that you kill

}