EEC-681/781 Distributed Computing Systems

1. EEC-681/781Distributed Computing Systems Lecture 6 Wenbing Zhao Department of Electrical and Computer Engineering Cleveland State University wenbing@ieee.org

2. Message-Oriented Communication • Persistence and Synchronicity in Communication • Message-oriented transient communication • Berkeley sockets • Message-passing interface • Message-oriented persistent communication • Message-queuing system • Message brokers (publish/subscribe) • Java message service • A copy of JMS tutorial is available at DCS server /software/activemq/jms-tutorial.pdf EEC-681: Distributed Computing Systems

3. Synchronous Communication • Client/Server computing is generally based on a model of synchronous communication: • Client and server have to be active at the time of communication • Client issues request and blocks until it receives reply • Server essentially waits only for incoming requests, and subsequently processes them EEC-681: Distributed Computing Systems

4. Synchronous Communication • Drawbacks of synchronous communication: • Client cannot do any other work while waiting for reply • Failures have to be dealt with immediately (the client is waiting) • In many cases the model is simply not appropriate (mail, news) EEC-681: Distributed Computing Systems

5. Asynchronous Communication • Message-oriented middleware: Aims at high-level asynchronous communication: • Processes send each other messages, which are queued • Sender need not wait for immediate reply, but can do other things • Middleware often facilitates fault tolerance EEC-681: Distributed Computing Systems

6. Persistent Communication • Persistent Communication – A message that has been submitted for transmission is stored by the communication system as long as it takes to deliver it to the receiver • E.g. from postal mail to e-mail EEC-681: Distributed Computing Systems

7. Transient Communication • TransientCommunication – A message is stored by the communication system only as long as the sending and receiving application are executing • All transport-level communication services offer only transient communication • RPC/RMI EEC-681: Distributed Computing Systems

8. Message-Oriented Transient Communication • Berkeley Sockets • Message-Passing Interface EEC-681: Distributed Computing Systems

9. Berkeley Sockets EEC-681: Distributed Computing Systems

10. Berkeley Sockets Connection-oriented communication pattern using sockets EEC-681: Distributed Computing Systems

11. The Message-Passing Interface (MPI) • MPI is used to do high performance computing on multicomputers • Use high-speed interconnection networks • Come with proprietary communication libraries • Need message-passing primitives at a convenient level of abstraction • Standard APIs, hardware-independent EEC-681: Distributed Computing Systems

12. Application A Application B Message-Oriented Middleware Messaging API Messaging API Messaging Clients Messaging Clients Message-Oriented Persistent Communication Message-Oriented Middleware (MOM) EEC-681: Distributed Computing Systems

13. Receiver Sender MOM Messages Characteristics of MOM • Loosely-coupled communication: They offer intermediate storage capacity for messages, without requiring either sender or receiver to be active during message transmission • Encompasses publish/subscribe and message queuingcommunications EEC-681: Distributed Computing Systems

14. Producer Queue Consumer send(m1) send(m2) receive() m1 Message Queuing Put message into queue Consume message A message queue offers point-to-point communication: each message produced has one consumer EEC-681: Distributed Computing Systems

15. Producer Consumer Consumer Publish/Subscribe Broker publish(m1) Pass message to broker send(m1) publish(m2) send(m1) Dispatch message to all consumers send(m2) send(m2) publish(m3) Publish/subscribe offers one-to-many communication: each message published can have many subscribers EEC-681: Distributed Computing Systems

16. Message Queuing Application EEC-681: Distributed Computing Systems

17. Publish/Subscribe Application publish(“EEC693”, HW1); publish(“EEC693”, HW2); publish(“EEC681”, Lab1); publish(“EEC681”, Lab2); subscribe (“EEC681”); subscribe (“EEC693”); subscribe (“EEC681”); subscribe (“EEC693”); subscribe (“EEC681”); EEC-681: Distributed Computing Systems

18. General Architecture of Message-Queuing System • Message queueing API provides a higher abstraction to application developers • Queue-level addressing is translated to transport-level addressing in MOM EEC-681: Distributed Computing Systems

19. General Architecture of Message-Queuing System • A message can be handled by a centralized message server, or routed by multiple queue managers • Scalability • Secondary processing of messages, e.g., logging, bridging EEC-681: Distributed Computing Systems

20. Java Message Service • Standard Java API • Message delivery models • Two messaging models • Transactions • Reliability levels • Persistent messaging EEC-681: Distributed Computing Systems

21. JMS Messaging Domains • Publish and subscribe (topic) • Many consumers per message • Point-to-point (queue) • One consumer per message EEC-681: Distributed Computing Systems

22. JMS Components JMS Client JMS Client Connection Connection Session Session Producer Consumer Message Server Destination Message Message EEC-681: Distributed Computing Systems

23. Connections and Sessions • A connection connects to a message server • You can create one or more sessions within a connection JMS Client Connection Session Session Session EEC-681: Distributed Computing Systems

24. Creating Connections and Sessions JMS Client ConnectionFactory create JNDI Store Message Server Connection ConnectionFactories Destinations Session Session Session EEC-681: Distributed Computing Systems

25. JMS Message Types EEC-681: Distributed Computing Systems

26. TopicSession QueueSession createStreamMessage( ) createTextMessage( ) TextMessage StreamMessage Creating a Message EEC-681: Distributed Computing Systems

27. Automatically assigned headers JMSDestination JMSDeliveryMode JMSMessageID JMSTimestamp JMSExpiration JMSRedelivered JMSPriority Developer-assigned headers JMSReplyTo JMSCorrelationID JMSType JMS Message Headers EEC-681: Distributed Computing Systems

28. Producers, Consumers, and Destinations Producer Consumer Bind to destination Bind to destination Read message Message Server Send message Consume message Destination EEC-681: Distributed Computing Systems

29. Creating Destinations JMS Client JNDI Store Message Server Topic ConnectionFactories Destinations lookup Queue EEC-681: Distributed Computing Systems

30. Producing a Message create message Session create Message Destination MessageProducer produce message EEC-681: Distributed Computing Systems

31. MessageListener onMessage(message) MessageConsumer Message receive() Consuming Messages Incoming messages Asynchronous Message Delivery acknowledge Message Server Incoming messages acknowledge Synchronous Message Delivery EEC-681: Distributed Computing Systems

32. Filtering with Message Selector Publisher Departments.Sales JMSPriority = 2 Pipeline = 20000 not delivered Subscriber delivered Subscriber Message Server Departments.Sales Pipeline > 20000 Departments.Sales Pipeline > 15000 not delivered delivered Subscriber Subscriber Departments.Sales JMSPriority > 5 Departments.Sales JMSPriority >= 2 AND Pipeline > 10000 EEC-681: Distributed Computing Systems

33. Browsing a Queue Message1 QueueBrowser Message2 getEnumeration() Message3 Enumeration nextElement() Message4 EEC-681: Distributed Computing Systems

34. Accessing Message Content get<type>(Name) Message MapMessage TextMessage ObjectMessage StreamMessage BytesMessage getText() getObject() read<type>() EEC-681: Distributed Computing Systems