在tornado中不阻塞创建子进程的一个工具类

process_util.py

#!/usr/bin/env python
#coding: utf-8 
import os
import shlex
import subprocess
import signal
import functools
import logging
import tornado

# Default daemon parameters.
# File mode creation mask of the daemon.
UMASK = 0

# Default working directory for the daemon.
WORKDIR = "/"

# Default maximum for the number of available file descriptors.
MAXFD = 1024

# The standard I/O file descriptors are redirected to /dev/null by default.
if (hasattr(os, "devnull")):
	REDIRECT_TO = os.devnull
else:
	REDIRECT_TO = "/dev/null"

signal.signal(signal.SIGCHLD,signal.SIG_IGN) #avoid defunct process

def fork_daemon_subprocess(cmd):
	"""Detach a process from the controlling terminal and run it in the
	background as a daemon.
	"""

	try:
		# Fork a child process so the parent can exit.  This returns control to
		# the command-line or shell.  It also guarantees that the child will not
		# be a process group leader, since the child receives a new process ID
		# and inherits the parent's process group ID.  This step is required
		# to insure that the next call to os.setsid is successful.
		pid = os.fork()
	except OSError, e:
		raise Exception, "%s [%d]" % (e.strerror, e.errno)

	if (pid == 0):	# The first child.
		# To become the session leader of this new session and the process group
		# leader of the new process group, we call os.setsid().  The process is
		# also guaranteed not to have a controlling terminal.
		os.setsid()

		# Is ignoring SIGHUP necessary?
		#
		# It's often suggested that the SIGHUP signal should be ignored before
		# the second fork to avoid premature termination of the process.  The
		# reason is that when the first child terminates, all processes, e.g.
		# the second child, in the orphaned group will be sent a SIGHUP.
		#
		# "However, as part of the session management system, there are exactly
		# two cases where SIGHUP is sent on the death of a process:
		#
		#	1) When the process that dies is the session leader of a session that
		#		is attached to a terminal device, SIGHUP is sent to all processes
		#		in the foreground process group of that terminal device.
		#	2) When the death of a process causes a process group to become
		#		orphaned, and one or more processes in the orphaned group are
		#		stopped, then SIGHUP and SIGCONT are sent to all members of the
		#		orphaned group." [2]
		#
		# The first case can be ignored since the child is guaranteed not to have
		# a controlling terminal.  The second case isn't so easy to dismiss.
		# The process group is orphaned when the first child terminates and
		# POSIX.1 requires that every STOPPED process in an orphaned process
		# group be sent a SIGHUP signal followed by a SIGCONT signal.  Since the
		# second child is not STOPPED though, we can safely forego ignoring the
		# SIGHUP signal.  In any case, there are no ill-effects if it is ignored.
		#
		# import signal			  # Set handlers for asynchronous events.
		# signal.signal(signal.SIGHUP, signal.SIG_IGN)

		try:
			# Fork a second child and exit immediately to prevent zombies.  This
			# causes the second child process to be orphaned, making the init
			# process responsible for its cleanup.  And, since the first child is
			# a session leader without a controlling terminal, it's possible for
			# it to acquire one by opening a terminal in the future (System V-
			# based systems).  This second fork guarantees that the child is no
			# longer a session leader, preventing the daemon from ever acquiring
			# a controlling terminal.
			pid = os.fork()	# Fork a second child.
		except OSError, e:
			raise Exception, "%s [%d]" % (e.strerror, e.errno)

		if (pid == 0):	# The second child.
			# Since the current working directory may be a mounted filesystem, we
			# avoid the issue of not being able to unmount the filesystem at
			# shutdown time by changing it to the root directory.
			#os.chdir(WORKDIR)
			# We probably don't want the file mode creation mask inherited from
			# the parent, so we give the child complete control over permissions.
			os.umask(UMASK)
		else:
			# exit() or _exit()?  See below.
			os._exit(0)	# Exit parent (the first child) of the second child.
	else:
		# exit() or _exit()?
		# _exit is like exit(), but it doesn't call any functions registered
		# with atexit (and on_exit) or any registered signal handlers.  It also
		# closes any open file descriptors.  Using exit() may cause all stdio
		# streams to be flushed twice and any temporary files may be unexpectedly
		# removed.  It's therefore recommended that child branches of a fork()
		# and the parent branch(es) of a daemon use _exit().
		
		# 因为这个agent进程还要继续运行，所以这里不需要exit
		# os._exit(0)	# Exit parent of the first child.
		return

	# Close all open file descriptors.  This prevents the child from keeping
	# open any file descriptors inherited from the parent.  There is a variety
	# of methods to accomplish this task.  Three are listed below.
	#
	# Try the system configuration variable, SC_OPEN_MAX, to obtain the maximum
	# number of open file descriptors to close.  If it doesn't exists, use
	# the default value (configurable).
	#
	# try:
	#	 maxfd = os.sysconf("SC_OPEN_MAX")
	# except (AttributeError, ValueError):
	#	 maxfd = MAXFD
	#
	# OR
	#
	# if (os.sysconf_names.has_key("SC_OPEN_MAX")):
	#	 maxfd = os.sysconf("SC_OPEN_MAX")
	# else:
	#	 maxfd = MAXFD
	#
	# OR
	#
	# Use the getrlimit method to retrieve the maximum file descriptor number
	# that can be opened by this process.  If there is not limit on the
	# resource, use the default value.
	#
	import resource		# Resource usage information.
	maxfd = resource.getrlimit(resource.RLIMIT_NOFILE)[1]
	if (maxfd == resource.RLIM_INFINITY):
		maxfd = MAXFD
  
	# Iterate through and close all file descriptors.
	for fd in range(0, maxfd):
		try:
			os.close(fd)
		except OSError:	# ERROR, fd wasn't open to begin with (ignored)
			pass

	# Redirect the standard I/O file descriptors to the specified file.  Since
	# the daemon has no controlling terminal, most daemons redirect stdin,
	# stdout, and stderr to /dev/null.  This is done to prevent side-effects
	# from reads and writes to the standard I/O file descriptors.

	# This call to open is guaranteed to return the lowest file descriptor,
	# which will be 0 (stdin), since it was closed above.
	os.open(REDIRECT_TO, os.O_RDWR)	# standard input (0)

	# Duplicate standard input to standard output and standard error.
	os.dup2(0, 1)			# standard output (1)
	os.dup2(0, 2)			# standard error (2)

	os.system(cmd)
	os.exit(0)

def call_subprocess_blocked(command, wait_until_exit=False):
	pipe = subprocess.Popen(shlex.split(command), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
	if wait_until_exit:
		pipe.poll()
	return (pipe.stdout, pipe.stderr, pipe.returncode)

def call_subprocess(context, command, wait_until_exit=False, callback=None):
	""" call subprocess and return (stdout,stderr,returncode) tuple to callback"""
	context.ioloop = tornado.ioloop.IOLoop.instance()
	context.pipe = p = subprocess.Popen(shlex.split(command), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
	async_callback_func = functools.partial(on_subprocess_result, context, callback, wait_until_exit)
	context.ioloop.add_handler(p.stdout.fileno(), async_callback_func, context.ioloop.READ|context.ioloop.ERROR)
 
def on_subprocess_result(context, callback, wait_until_exit, fd, result):
	""" invoke callback with (stdout,stderr,returncode) """
	try:
		if callback:
			if wait_until_exit:
				context.pipe.poll()
			callback((context.pipe.stdout, context.pipe.stderr, context.pipe.returncode))
	except Exception, e:
		logging.error(e)
	finally:
		context.ioloop.remove_handler(fd)

if __name__ == '__main__':
	import time
	os.chdir('/Users/arbow/test')
	fork_daemon_subprocess('sh ./start.sh')
	time.sleep(1)
	print 'Main process exit now'