Changed persistent module to use shelve dictionaries

sys/persistent.py

@@ -1,49 +1,90 @@
-from ConfigParser import ConfigParser
+import shelve
-import cPickle as pickle
-import base64
 from threading import Lock
-#TODO  replace ConfigParser for better performance
 
 class PersistentContainer(object):
-	cfgparsers = dict()
+	"""A wrapper for shelve dictionaries, allowing basic transactions and namespaces
-	locks = dict()
+	Be carefull as this module returns copies but no references. This means it needs
+	careful programming:
+
+		>>> pc = PersistentContainer("ns","foobar")
+		>>> pc["num"] = 3 		 # direct access using = operators works
+		>>> pc["list"] = [1,2,3] 
+		>>> pc["num"] += 3       # this will work...
+		>>> print pc["num"]
+		6
+		>>> pc["list"].append(4) # ...but this wont.
+		>>> print pc["list"]
+		[1, 2, 3]
+		>>> tmp = pc["list"]	 # instead store a copy
+		>>> tmp.append(4)        # alter the copy
+		>>> pc["list"]=tmp       # and write it back
+		>>> print pc["list"]
+		[1, 2, 3, 4]
+	"""
+	refs = dict()
 	def __init__(self,namespace,path):
+		"""Create a PersistentContainer object
+		namespace -- the namespace in which the variables will be saved
+		path      -- path to the (n)dbm-file used to permanently store the values
+		"""
 		self.namespace = namespace
 		self.path = path
 		self.trans_cache = dict()
 		self.trans_del = []
 
-		if not path in PersistentContainer.locks:
+		if not path in PersistentContainer.refs:
-			PersistentContainer.locks[path] = Lock()		
+			ref_cnt = 0
-		self.transaction = PersistentContainer.locks[path]
+			lock = Lock()	
-
+			dic = shelve.open(path,writeback=False)
-		if not path in PersistentContainer.cfgparsers:
+			PersistentContainer.refs[path] = [ref_cnt,lock,dic]
-			PersistentContainer.cfgparsers[path] = ConfigParser()
+		ref = PersistentContainer.refs[path]
-			PersistentContainer.cfgparsers[path].read([path])
+		ref[0]+=1
-		self.cp = PersistentContainer.cfgparsers[path] 
+		self.transaction = ref[1]
-
+		self.dic = ref[2]
-		if not self.cp.has_section(namespace):
+
-			self.cp.add_section(namespace)
+	def __del__(self):
+		"""delete the object"""
+		assert self.path in PersistentContainer.refs
+		ref = PersistentContainer.refs[self.path]
+		ref[0] -= 1
+		if ref[0]==0:
+			self.dic.close()
+			del PersistentContainer.refs[self.path]
 
 	def start_transaction(self,blocking=True):
+		"""Start an atomic transaction.
+		blocking -- If True the start of the transaction will wait until the running
+	                is finished
+		"""
 		return self.transaction.acquire(blocking)
 
 	def commit_transaction(self):
+		"""Commit the values that changed during the transaction"""
 		self._write()
 		self.transaction.release()
 
 	def rollback(self):
-		for k in self.trans_cache:
+		"""Discard the values that changed during the transaction"""
+		for k in self.trans_cache.keys():
 			del self.trans_cache[k]
 		self.transaction.release()
 		
+	def keys(self):
+		"""Return the valid keys in the namespace"""
+		ret = []
+		for k in self.dict.keys():
+			if k.endswith("."+self.namespace):
+				ret.append(k[:-len("."+self.namespace)])
+		return ret
+
 	def is_owned(self):
+		"""Return True if there is an transaction running"""
 		return self.transaction.locked()
 
 	def __getitem__(self, name):	
-		if self.cp.has_option(self.namespace,name):
+		key = name+"."+self.namespace
-			b64 = self.cp.get(self.namespace,name)
+		if key in self.dic:
-			return pickle.loads(base64.b64decode(b64))
+			return self.dic[key]
 		return None
 
 	def __setitem__(self, name,val):
@@ -61,18 +102,18 @@ class PersistentContainer(object):
 
 
 	def __contains__(self,name):
-		return self.cp.has_option(self.namespace,name)
+		key = name+"."+self.namespace
+		return key in self.dic
 
 	def _write(self):
-		for k in self.trans_cache:
+		for name in self.trans_cache.keys():		
-			val = self.trans_cache[k]
+			key = name+"."+self.namespace
-			ser = pickle.dumps(val)
+			val = self.trans_cache[name]
-			self.cp.set(self.namespace,k,base64.b64encode(ser))	
+			self.dic[key]=val
+			del self.trans_cache[name]
 		while len(self.trans_del):
-			n = self.trans_del.pop()
+			name = self.trans_del.pop()
-			self.cp.remove_option(self.namespace,n)
+			key = name+"."+self.namespace
-
+			del self.dic[key]
-		f = open(self.path,'w')
+		self.dic.sync()
-		self.cp.write(f)
-		f.close()