#!/usr/bin/env perl
require 5.003;
use warnings;
$indent=4;

#
# Copyright by The HDF Group.
# All rights reserved.
#
# This file is part of HDF5.  The full HDF5 copyright notice, including
# terms governing use, modification, and redistribution, is contained in
# the COPYING file, which can be found at the root of the source code
# distribution tree, or in https://www.hdfgroup.org/licenses.
# If you do not have access to either file, you may request a copy from
# help@hdfgroup.org.
#

# Run program in background
#
use warnings;
use strict;

use Carp;
use Time::HiRes;
use POSIX 'setsid';

my $child_pid;
my $child_proc;
my $cmd = $ARGV[0];
my $debug = 1;

print "\nStart child process\n";
start_child();
print "\nStarted child process\n";

sub start_child {
    die "cannot execute cmd: $cmd" unless -x $cmd;
    if ($^O eq 'MSWin32') { # Windows
        require Win32::Process;
        Win32::Process::Create($child_proc, $cmd, $cmd, 0, 0, ".") || confess "Could not spawn child: $!";
        $child_pid = $child_proc->GetProcessID();
    }
    else { # Unix
        $SIG{CHLD} = 'IGNORE';
        $child_pid = fork();
        unless (defined $child_pid) {
            confess "Could not spawn child (Unix): $!";
        }
        if ($child_pid == 0) { # child
            unless ($debug) {
                open STDIN, "<", "/dev/null"   or die "Can't read /dev/null: $!";
                open STDOUT, ">", "/dev/null"  or die "Can't write /dev/null: $!";
            }
            setsid or warn "setsid cannot start a new session: $!";
            unless ($debug) {
                open STDERR, '>&STDOUT'  or die "Can't dup stdout: $!";
            }
            local $| = 1;
            unless (exec($cmd)) {
                confess "Could not start child: $cmd: $!";
                CORE::exit(0);
            }
        }
        # parent
        $SIG{CHLD} = 'DEFAULT';
    }
    # catch early child exit, e.g. if program path is incorrect
    sleep(1.0);
    POSIX::waitpid(-1, POSIX::WNOHANG()); # clean up any defunct child process
    if (kill(0,$child_pid)) {
        print "\nStarted child process id $child_pid\n";
    }
    else {
        warn "Child process exited quickly: $cmd: process $child_pid";
    }
}

sub stop_child
{
    if ($^O eq 'MSWin32') { # Windows
        Win32::Process::KillProcess($child_pid,0);
    }
    else { # Unix
        kill 9, $child_pid || warn "could not kill process $child_pid: $!";
    }
    print "Stopped child process id $child_pid\n";
}