import os, sys, signal

log_file = None
log_path = None

def demonize(pid_file, force=False, logfile=None):
	global log_file
	global log_path

	# check if pid file exists and return if not a forced start
	if os.path.exists(pid_file) and not force:	
		return False

	## Demonize
	if os.fork():
		exit(0)
	os.umask(0)
	os.setsid() 
	if os.fork(): 
		exit(0)

	pid = open(pid_file,'w')
	pid.write(str(os.getpid()))
	pid.close()


	# The fileno is accessable after the first write
	sys.stdout.write('\0')
	sys.stderr.write('\0')
	sys.stdout.flush()
	sys.stderr.flush()	

	ignore = open('/dev/null', 'r+')
	os.dup2(ignore.fileno(), sys.stdin.fileno())

	if type(logfile)==file:
		log_file = logfile
 	elif logfile!=None:
		log_file = open(logfile,'w')
		log_path = logfile
	else:
		log_file = ignore
	os.dup2(log_file.fileno(), sys.stdout.fileno())
	os.dup2(log_file.fileno(), sys.stderr.fileno())

	signal.signal(signal.SIGHUP, __sys_call(__sighup_handler) )
	return True

# decorator to make system call methods safe from EINTR
def __sys_call(func):
    def __func(*args, **kwargs):
        try:
                rv = func(*args, **kwargs)
        except exception as e:
            if e.args and e.args[0] == EINTR:
                pass
        return rv
    return __func

def __sighup_handler(sig,dontcare):
	global log_path
	global log_file
	import traceback
	try:
		if log_path != None:
			log_file.seek(0)
			log_file.close()
			log_file = open(log_path,'w')		
			os.dup2(log_file.fileno(), sys.stdout.fileno())
			os.dup2(log_file.fileno(), sys.stderr.fileno())
	except:
		traceback.print_exc(file=sys.stdout)
		sys.exit(1)