SF.net SVN: fclient:[818] trunk/fclient/src/fclient/impl/lib/qt4ex/ singleapp.py

[<jU...@us...>]

Revision: 818
          http://fclient.svn.sourceforge.net/fclient/?rev=818&view=rev
Author:   jUrner
Date:     2008-07-30 10:47:21 +0000 (Wed, 30 Jul 2008)

Log Message:
-----------
add a module to control single application stuff

Added Paths:
-----------
    trunk/fclient/src/fclient/impl/lib/qt4ex/singleapp.py

Added: trunk/fclient/src/fclient/impl/lib/qt4ex/singleapp.py
===================================================================
--- trunk/fclient/src/fclient/impl/lib/qt4ex/singleapp.py	                        (rev 0)
+++ trunk/fclient/src/fclient/impl/lib/qt4ex/singleapp.py	2008-07-30 10:47:21 UTC (rev 818)
@@ -0,0 +1,106 @@
+"""making resonably shure only one appliaction is running at a time""" 
+ 
+
+import socket
+import thread
+#**********************************************************************
+#
+#**********************************************************************
+class ErrorCanNotConnect(Exception):
+	"""exception raised in cace SignleApp can not connect to the socket or something unexpected happens in the communication"""
+	
+class ErrorOtherAppIsRunning(Exception):
+	"""exception raised when SingleApp detects another application is already running"""
+	
+
+class SingleApp(object):
+	"""Class doing its best to enshure only one instance of an application
+	is running at the same time
+	
+	@note: the class uses a socket to exchange data in between applications. firewalls
+	(...) may not like this. 
+	@note: a carefuly chosen magic string to exchange may help to reduce the chance
+	of accidential collisions with other applications
+	@note: race conditions? yes
+	"""
+	
+	def __init__(self, host=None, port=None, magicToSend=None, magicToRespond=None, userData=None):
+		"""
+		@param host: host to establish the connection to
+		@param port: port to use for the connection
+		@param magicToSend: magic string a client should send to the server
+		@param magicToRespond: magic string the server should send in response
+		@param userData: any data you want to associate to the SignleApp object
+		"""
+				
+		if host is None or port is None or magicToSend is None or magicToRespond is None:
+			raise ValueError('All keyword arguments except userData are mandatory. This is just for better looks')
+		self.host = host
+		self.port = port
+		self.magicToSend = magicToSend
+		self.magicToRespond = magicToRespond
+		self.isServerRunning = False
+		self.socket = None
+		self.userData = userData
+			
+	
+	def _runServer(self):
+		# start server and listen to incoming connections
+		while True:
+			self.socket.listen(1)
+			conn, addr = self.socket.accept()
+			# NOTE: my best guess here is that we can not loop here to make shure we
+			# get some data. mybe the other end of the pipe plays dead
+			data = conn.recv(len(self.magicToSend))
+			if data == self.magicToSend:
+				self.onOtherAppIsStarting()
+				conn.send(self.magicToRespond)
+			conn.close()
+		self.socket.close()
+		self.socket = None
+		self.isServerRunning = False
+	
+		
+	def start(self):
+		"""starts SingleApp
+		
+		@raise ErrorCanNotConnect:
+		@raise ErrorOtherAppIsRunning:
+		"""
+		# try to bind socket as server
+		self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+		self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+		try:
+			self.socket.bind((self.host, self.port))
+		except socket.error, details:
+			# assume address is already in use, try to connect to it
+			try:
+				self.socket.connect((self.host, self.port))
+			except socket.error, details:
+				# ups, neither way works. we give up here
+				raise ErrorCanNotConnect(details)
+			try:
+				# try to find out who is serving
+				self.socket.settimeout(0.5)	
+				self.socket.sendall(self.magicToSend)
+				# NOTE: my best guess here is that we can not loop here to make shure we
+				# get some data. mybe the other end of the pipe plays dead 
+				data = self.socket.recv(len(self.magicToRespond))
+				if data == self.magicToRespond:
+					raise ErrorOtherAppIsRunning()
+			except socket.timeout:
+				raise ErrorCanNotConnect(details)
+			finally:
+				self.socket.close()
+				self.socket = None
+		else:
+			self.isServerRunning = True
+			thread.start_new_thread(self._runServer, ())
+						
+	def onOtherAppIsStarting(self):
+		"""called when another application using the same magic string is conncting to our server"""
+		print 'another app of the same kind is connecting to us'
+	
+	
+		
+	


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