Simple RDF store in ZooKeeper

simple-rdf-store.py

import zookeeper, threading, sys

ZOO_OPEN_ACL_UNSAFE = {"perms":0x1f, "scheme":"world", "id" :"anyone"};

class ZKSimpleRDFStore(object):
	SERVER_PORT = 2181

	def __init__(self):
		self.host = "localhost:%d" % self.SERVER_PORT
		self.connected = False
		self.handle = -1
		try:
			f = open('simple-rdf-store.log','w')
			zookeeper.set_log_stream(f)
		except IOError:
			print "Couldn't open logfile for writing"

	def set_up(self):
		self.callback_flag = False
		self.cv = threading.Condition()
		self.connected = False
		def connection_watcher(handle, type, state, path):
			self.cv.acquire()
			self.connected = True
			self.cv.notify()
			self.cv.release()

		self.cv.acquire()
		self.handle = zookeeper.init(self.host, connection_watcher)
		self.cv.wait(10.0)
		self.cv.release()

		if not self.connected:
			raise Exception("Couldn't connect to host -", self.host)

	def new_con(self):
		cv = threading.Condition()
		self.pending_connection = False
		def connection_watcher(handle, type, state, path):
			cv.acquire()
			self.pending_connection = True
			cv.notify()
			cv.release()

		cv.acquire()
		handle = zookeeper.init(self.host, connection_watcher)
		cv.wait(15.0)
		cv.release()

		if not self.pending_connection:
			raise Exception("Couldn't connect to host -", self.host)
		return handle

	def shut_down(self):
		if self.connected:
			zookeeper.close(self.handle)	

	def exists_ng(self, ng):
		return zookeeper.exists(self.handle, ng, None)
	
	def get_ng(self, ng):
		return zookeeper.get(self.handle, ng, None)

	# adds a named graph and overwrites the content in case it exists already
	def put_ng(self, ng, val):
		ret = None
		if self.exists_ng(ng):
			(data, stat) = self.get_ng(ng)
			zookeeper.set(self.handle, ng, val, stat["version"])
		else:
			zookeeper.create(self.handle, ng, val, [ZOO_OPEN_ACL_UNSAFE], zookeeper.EPHEMERAL)
		return self.get_ng(ng)
              
if __name__ == '__main__':
	zkSRS = ZKSimpleRDFStore()
	
	print 'Set up of Simple RDF Store ...'
	zkSRS.set_up()
	
	(data, stat) = zkSRS.put_ng('/ng-0', '<http://data.example.org/person/tim> dc:publisher "Tim" .')
	print stat
	print data
		
	print "Done"