monitor.py

'''
Code change monitor for use with Apache WSGI module

Source: http://code.google.com/p/modwsgi/wiki/ReloadingSourceCode
'''

import os
import sys
import time
import signal
import threading
import atexit
import Queue

_interval = 1.0
_times = {}
_files = []

_running = False
_queue = Queue.Queue()
_lock = threading.Lock()

def _restart(path):
	_queue.put(True)
	prefix = 'monitor (pid=%d):' % os.getpid()
	print >> sys.stderr, '%s Change detected to \'%s\'.' % (prefix, path)
	print >> sys.stderr, '%s Triggering process restart.' % prefix
	os.kill(os.getpid(), signal.SIGINT)

def _modified(path):
	try:
		# If path doesn't denote a file and were previously
		# tracking it, then it has been removed or the file type
		# has changed so force a restart. If not previously
		# tracking the file then we can ignore it as probably
		# pseudo reference such as when file extracted from a
		# collection of modules contained in a zip file.

		if not os.path.isfile(path):
			return path in _times

		# Check for when file last modified.

		mtime = os.stat(path).st_mtime
		if path not in _times:
			_times[path] = mtime

		# Force restart when modification time has changed, even
		# if time now older, as that could indicate older file
		# has been restored.

		if mtime != _times[path]:
			return True
	except:
		# If any exception occured, likely that file has been
		# been removed just before stat(), so force a restart.

		return True

	return False

def _monitor():
	while 1:
		# Check modification times on all files in sys.modules.

		for module in sys.modules.values():
			if not hasattr(module, '__file__'):
				continue
			path = getattr(module, '__file__')
			if not path:
				continue
			if os.path.splitext(path)[1] in ['.pyc', '.pyo', '.pyd']:
				path = path[:-1]
			if _modified(path):
				return _restart(path)

		# Check modification times on files which have
		# specifically been registered for monitoring.

		for path in _files:
			if _modified(path):
				return _restart(path)

		# Go to sleep for specified interval.

		try:
			return _queue.get(timeout=_interval)
		except:
			pass

_thread = threading.Thread(target=_monitor)
_thread.setDaemon(True)

def _exiting():
	try:
		_queue.put(True)
	except:
		pass
	_thread.join()

atexit.register(_exiting)

def track(path):
	if not path in _files:
		_files.append(path)

def start(interval=1.0):
	global _interval
	if interval < _interval:
		_interval = interval

	global _running
	_lock.acquire()
	if not _running:
		prefix = 'monitor (pid=%d):' % os.getpid()
		print >> sys.stderr, '%s Starting change monitor.' % prefix
		_running = True
		_thread.start()
		_lock.release()