From: Constantin Berhard <constantin@exxxtremesys.lu>
Date: Sun, 27 Oct 2013 10:14:59 +0000 (+0100)
Subject: concept spaceAPI + Locking
X-Git-Url: https://git.ralfj.de/saartuer.git/commitdiff_plain/faba368ee235609ed7ff9d32bbf0a892eef0ddb2?ds=inline;hp=226118cbaed9b2f092e2ae764260bf3b63951938

concept spaceAPI + Locking
---

diff --git a/concept_spaceapi.py b/concept_spaceapi.py
index 472b26d..0f251d7 100644
--- a/concept_spaceapi.py
+++ b/concept_spaceapi.py
@@ -1,24 +1,40 @@
-
+from threading import Lock
 
 class SpaceApi:
 	__init__ (self, waker):
-		self._state_to_set = None # public write
-		self._state_last_set = None # public read FIXME why? getter?
+		self._state_to_set = None
+		self._state_last_set = None
 		self._running = True
 		self.set_state = ThreadFunction(self._set_state, "Space API")
+		self._set_state_lock = Lock()
 		waker.register(self.set_state, 10.0) # re-try setting the state every 10 seconds
 	
 	def stop (self):
 		self.set_state.stop()
 	
+	# set_state is the asynchronous version of _set_state (see __init__)
 	def _set_state (self, state = None):
 		'''Sets the state, if None: leave state unchanged and re-try if previous attempts failed'''
 		if state is not None:
 			self._state_to_set = state
-		# check if there's something we need to do
-		if self._state_last_set == self._state_to_set: return
-		# take action!
-		error = do_request(stts) # TODO
-		#TODO logging
-		if not error:
-			self.state_last_set = stts
+		else:
+			# always have a local variable because of parallelism
+			state = self._state_to_set
+		
+		if not self._set_state_lock.acquire(False):
+			# we don't want many threads to wait here
+			# the next status update will fix everything anyways
+			pass
+		else:
+			# got the lock
+			try:
+				# check if there's something we need to do
+				if self._state_last_set == state: return
+				# take action!
+				error = do_request(stts) # TODO
+				#TODO logging
+				#TODO error too often -> log critical to send mails
+				if not error:
+					self.state_last_set = stts
+			finally:
+				self._set_state_lock.release()