C. Varela, RPI1 Distributed Computing with Python Carlos Varela Rensselaer Polytechnic Institute

C. Varela, RPI2 Distributed Computing with Python Using standard TCP/IP (or UDP) sockets Using high-level libraries for remote method invocation –XML-RPC –Pyro (PYthon Remote Objects)

C. Varela, RPI3 Networking with Python Sockets Resembles C socket API Can use UDP (datagrams) or TCP (streamed connections) Does not require “non-standard” libraries Low-level, yet relatively easy to use and portable Enables more efficient communication and is programming language independent. New features require protocol extensions

C. Varela, RPI4 Sockets: An Echo Server from socket import * def main(): s = socket(AF_INET, SOCK_STREAM) s.bind((‘’, 50007)) # port number s.listen(1) conn, (remotehost, remoteport) = s.accept() print 'connected by', remotehost, remoteport while 1: data = conn.recv(1024) # buffer size if not data: break conn.send(data) conn.close() main()

C. Varela, RPI5 Sockets: An Echo Client from socket import * def main(): s = socket(AF_INET, SOCK_STREAM) s.connect((‘localhost’, 50007)) # port number s.send(‘Hello World’) data = s.recv(1024) # buffer size s.close() print data main()

C. Varela, RPI6 Remote Procedure Calls with Python XML-RPC library XML-RPC is programming-language/O.S. independent Uses XML as message format for parameters and return values, e.g.: Hello World Uses HTTP as the transport protocol. Enabling technology for building “web services”. Example requires downloading xmlrpcserver.py library:

C. Varela, RPI7 XML-RPC: An Echo Server import SocketServer; import xmlrpcserver; import xmlrpclib class EchoReqHandler(xmlrpcserver.RequestHandler): def call(self, method, params): print "Dispatching: ", method, params try: server_method = getattr(self, method) except: raise AttributeError, ”No method: %s" % method return server_method(params) def echo(self, value): return xmlrpclib.dumps(value) server = SocketServer.TCPServer(('', 8000), EchoReqHandler) server.serve_forever()

C. Varela, RPI8 XML-RPC: An Echo Client import xmlrpclib echosvr = xmlrpclib.Server(" print echosvr.echo("Hello World") print echosvr.echo(10)

C. Varela, RPI9 Distributed Computing with Python Remote Objects (PYRO) Resembles Java RMI: Server Daemon, Client Proxy To find remote objects: –By name, e.g., “PYRONAME://echo”, requires name server –By location, e.g., “PYROLOC://localhost:7766/echo” –By URI, e.g., “PYRO:// :7766/7f b1892e90a71” Method arguments, return values, and exceptions marshalled (“pickled”) over the network Example code requires downloading and installing Pyro at:

C. Varela, RPI10 Pyro: An Echo Server import Pyro.core class Echo(Pyro.core.ObjBase): def __init__(self): Pyro.core.ObjBase.__init__(self) def echo(self, string): return string; Pyro.core.initServer() daemon=Pyro.core.Daemon() uri=daemon.connect(Echo(),"echo-object") print "The object's uri is:",uri daemon.requestLoop()

C. Varela, RPI11 Pyro: An Echo Client import Pyro.core echoProxy = Pyro.core.getProxyForURI( "PYROLOC://localhost:7766/echo-object") print echoProxy.echo("Hello World")

C. Varela, RPI12 Python Remote Objects (PYRO) Python programming language-dependent Event server for publish-subscribe communication Mobile code, but BEWARE: No security guarantees!

C. Varela, RPI13 Exercises 1.Compare the round trip time of the Echo application using: TCP/IP XML-RPC Pyro 2.Use the XML-RPC client in Python to connect to an existing web service (e.g., Google) 3.Modify the echo example in Pyro to use the name service. What are alternative ways to get to the name server? 4.Does Pyro support distributed garbage collection?