Message-oriented Communication

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Transcript Message-oriented Communication

CIS007-3 Comparative Integrated
Systems
Communication including Message
Oriented Middleware
(Remote Procedure Call, Message and
Stream-Oriented Communication)
Sue Brandreth
1
Outline
• Introduction
• Fundamentals: Layered Protocols, Middleware,
Types of Communication
• (Remote Procedure Call (RPC))
• Message-Oriented Communication
– Transient communication
– Persistent communication
• (Stream-Oriented Communication)
2
INTRODUCTION
3
Review
• In a distributed system, processes
– run on different machines
– exchange information through message
passing
• Successful distributed systems depend on
communication models that hide or
simplify message passing
4
Interprocess Communication
• Modern distributed systems consist of thousands
or even millions of processes scattered across a
network such as the Internet
– To study distributed systems we need to examine how
processes on different machines exchange information
– Challenge: the underlying network is unreliable!
• Interprocess communication is at the heart of all
distributed systems
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Interprocess Communication
• How can processes on different remote machines
exchange information?
– No primitives based on shared memory (like in nondistributed parallel systems)
• Communication in distributed systems
– Based on low-level message passing
– Offered by the underlying network
– Harder than using shared memory
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Three Models for Communication
Three widely used models for communication:
• Remote Procedure Call (RPC)
– Hide most of the intricacies of message passing
– Ideal for client/server applications
• Message-Oriented Middleware (MOM)
– High-level message queuing model, similar to email
– Communication does not follow the rather strict pattern of
client/server interaction.
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Three Models for Communication
• Data Streaming (Stream Oriented Communication)
– Used in multimedia distributed systems
– Provides support for communication of continuous media, such as
audio and video
– Stream: continuous flow of messages
– Subject to various timing constraints
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Layered Protocols; Middleware; Types of
Communication
FUNDAMENTALS
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Layered Protocols: OSI Model
Layers, interfaces, and protocols in the OSI model.
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Layered Protocols: Headers
A typical message as it appears on the network.
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What is Middleware?
• An application that logically lives (mostly) in the
application layer
• Contains many middleware protocols
– General purpose
– Application independent
• “Glue” between actual applications and lower-level layers
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What is Middleware?
•
•
•
•
•
•
Provides a communication infrastructure for application
On top of a distributed system
Provides an API
Data transformation
Error handling
Localization and identification of client and server
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Types of Middleware
• Remote Procedure Call (RPC)
– Historic interest
• Object-Oriented Middleware (OOM)
– Java RMI
– CORBA
• Message-Oriented Middleware (MOM)
– Java Message Service
– IBM MQSeries
– Web Services
• Event-Based Middleware
• Transaction Processing Monitors (TPM)
• Object Request Brokers (ORB)
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Message Oriented Middleware
Message Oriented Middleware (or “MOM”) is one
particular form of middleware, which is capable of
facilitating the transportation of asynchronous
messages from one component to another.
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Middleware Protocols
• Used for establishing various middleware services
• Example Middleware protocols:
– Authentication and authorisation protocols
• Not closely tied to any specific application, but a general
service
– Distributed commit protocol
• All processes carry out an operation or the operation is not
carried out at all
– Distributed locking protocol
• Shared resource can be protected against simultaneous
access by a collection of processes being distributed across
multiple machines
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Middleware Communication Protocols
• Support high-level communication services, ie.
– Call a procedure or invoke an object on a remote machine
(in a highly transparent way)
– Message-passing services (comparable to those offered by
the transport layer).
– Reliable multicast-services
• Scale to thousands of receivers across a wide-area network
• Must be implemented with application requirements in mind
(hence in Middleware rather than in transport layer)
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Adapted Communication Reference Model
An adapted reference model for networked communication.
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COMMUNICATION MODELS
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Classification based on type of content:
• Events
• Commands
• Data
• Streams
Quiz Time
Quiz Time
Quiz Time
Quiz Time
Quiz Time
Quiz Time
Quiz Time
Quiz Time
Types of Communications
• Middleware offers the various alternatives in
communication to applications
• Types of communication can be classified along
several dimensions:
– Persistent vs. transient
– Synchronous vs. asynchronous
– Discrete vs. streaming
• Various combinations are possible
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Persistent vs. Transient
Communication
• Persistent communication
– Message stored by the communication middleware as long
as it takes to deliver it
– Sender can terminate after executing send. Sending
application does not need to continue execution after
submitting the message (allows for asynchronous
communication)
– Receiving application need not be executing when the
message is submitted. Receiver will get message next time
it runs.
– Example: email systems
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Persistent vs. Transient
Communication
• Transient communication
– Message is stored by the communication system only as
long as the sending and receiving applications are
executing.
– Communication errors or inactive receiver cause the
message to be discarded
– Transport-level communication is transient
– If the middleware cannot deliver a message due to a
transmission interrupt, or because the recipient is
currently not active, the message will simply be discarded
– Example: transport-level communication services (being
built upon traditional store-and-forward routers – if the
router can’t deliver, it drops the message)
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Persistent vs. Transient
Communication
Persistent communication: A message is stored at a
communication server as long as it takes to deliver
it to the receiver.
Transient communication: A message is discarded
by a communication server as soon as it cannot be
delivered at the next server, or at the receiver.
Asynchronous vs. Synchronous
Communication
• Asynchronous communication
– Sender continues execution immediately after it has
submitted its message to the middleware software
– Message is (temporarily) stored immediately by the
middleware upon submission
– Non-blocking
• Synchronous communication
–
–
–
–
Sender is blocked until its request is known to be accepted ie.
The OS or middleware notifies acceptance of the message, or
The message has been delivered to the receiver, or
The receiver processes it and returns a response
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Synchronous Communication
Some observations: 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
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)
Synchronous Communication:
Three Synchronization Points
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Asynchronous Communication:
Messaging
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 ensures fault tolerance
Discrete vs. Streaming
Communication
• Discrete
– All communicating parties communicate by
messages
• Each message forms a complete unit of information
• Streaming
– Messages are related to each other
• By the order they are sent
• By their temporal relationship
• One-way communication; a “session” consists of
multiple messages from the sender that are related
either by send order (TCP streams), temporal
proximity (multimedia streams), etc.
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Combinations
Various combinations of persistent/transient with
asynchronous/synchronous communications exist in
practice, ie.
• Persistence combined with synchronisation at
request submission
– a common scheme for many message-queuing systems
• Transient communication with synchronisation
after the request has been fully processed
– a scheme for Remote Procedure Calls
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Messaging Combinations
Important…..
• RPC supports access transparency, but is not
always appropriate
• RPC is usually synchronous, and is transient
• Message-oriented communication is more flexible
MESSAGE-ORIENTED
COMMUNICATION
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Message-Oriented Middleware (MOM)
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•
•
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Communication using messages
Messages stored in message queues
Message servers decouple client and server
Various assumptions made about message content
Client App.
Server App.
Message
Servers
local message
queues
message
queues
local message
queues
Network
Network
Network
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Forms of MOM
Forms of MOM:
• Message Queuing
• Publish-Subscribe
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Message-Oriented Persistent
Communication
Message Queuing Systems or Message-Oriented
Middleware (MOM)
• Important class of message-oriented middleware
services
• Persistent asynchronous communication
• Offer intermediate-term storage capacity for messages
• No need for either the sender or receiver to be active
during message transmission
• Support message transfers that are allowed to take
minutes.
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Properties of MOM
Asynchronous interaction
– Client and server are only loosely coupled
– Messages are queued
– Good for application integration
Support for reliable delivery service
– Keep queues in persistent storage
Processing of messages by intermediate message
server(s)
– May do filtering, transforming, logging, …
– Networks of message servers
Natural for database integration
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Message-Queuing Model
• Basic idea: applications communicate by inserting
messages in specific queues
• Messages forwarded over a series of communication
servers before being finally being delivered to the
destination
• Receiver can be down when message was sent
• No need for the sender to be executing when a message
is picked up by the receiver
• Sender is offered the guarantee that its message will
eventually be inserted into the recipient’s queue, but
no guarantee about when
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Message-Oriented Middleware
• Persistent. Processes
communicate through
message queues
– Queues are maintained
by the message-queuing
system
– Sender appends to
queue, receiver removes
from queue
– Neither the sender nor
receiver needs to be online when the message is
transmitted
Synchronous Communication
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Synchronous Communication
Also known as ‘Rendevouz’
• Tightly coupled
Pros:
• Client is informed about message delivery
• No buffering necessary
Cons:
• Sender and receiver have to run on the same time
• Direct connection necessary
• Client is blocked
• Lower degree of parallelity
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Asynchronous (Persistent)
Communication
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Asynchronous (Persistent)
Communication
• Loosely coupled
Pros:
• Higher degree of parallelity
• Enables faster sending than transmitting
• May compensate speed deviation between sender and
receiver (but not speed differences)
• Sender and receiver have not to run on the same time
Cons:
• Complicates synchronisation
• Sender has no information about message delivery
• Possible buffer overflows
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Asynchronous (Persistent)
Communication
• Asynchronous data transport between processes
• Data is transmitted in messages
• Based on queues
– Sender puts messages into a queues
– Message is transmitted to receiver
– Receiver reads message from queues
• Usually FIFO
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Queues
• Are named message destination that serve as an
intermediate between sender and receiver
• Allow processes to execute and fail independently
• Can mask process failures and communication
failures
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Message Priorities – Highest
Priority First
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Message Priorities – Weighted Fair
Scheduling
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Message Oriented Middleware
• Additional / Optionally
–
–
–
–
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Support of multiple Messaging models
Queue management
Connection Management
Quality-of-Service (QoS)
Data transformation
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Queue Manager
• Is a specialized kind of database
• Provides queuing functionality via an API to
applications
• Provides means for administration
–
–
–
–
Creation/deletion of queues
Allows to start and to stop queues
Alter properties of existing queues
Allows monitoring of performance, failures, and
recoveries
• Often queue managers can be configured to forward
messages to other queue managers
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Additional / Optional Queue Manager
Functionality
• Often called Message Broker
• Message Transformation
– Primary function = Reformatting data/information
– “Rosetta stone” of the system -> universal translation
– Understands the structure/formats of sources and targets
• Intelligent Routing
– Flow control
– See ‘Content based routing’
– Message Dictionary
•
•
•
•
Rules Engine
Repository
Filtering
Access control
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MOM – Message Oriented
Middleware
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Time Decoupling by Queues
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Location Decoupling by Queues
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Types of Message Based
Communication
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Asynchronous Persistent
• Most important Quality of Service is guaranteed delivery
• Possible failures:
– Receiver is not running.
– No connection to receiver.
• Guaranteed delivery by persistent storage on
intermediate nodes
– ie. as a file or in database
• If the receiver is up again or if the connection is available,
message is delivered.
• Guaranteed delivery but not always in time.
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Queuing Messaging Pattern
• One-to-One
– One sender, one receiver
– Point-to-Point
– Message Passing (MP)
• One-to-Many
– One sender, many receivers
• Many-to-One
– Many senders, one receiver
• Many-to-Many
– Many senders, many receivers
– -> Publish and Subscribe
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Message Passing / Point-to-Point
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Publish and Subscribe
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Publish/Subscribe Model
• One important and common use of a Message Broker is to
help form the Publish/Subscribe model (paradigm)
• In such a model, a broker is responsible not only for
converting messages but also for matching applications
based on the messages that are being exchanged
• Applications may publish a message on topic X by sending
it to the broker
• Applications with interest in messages on topic X can
subscribe to these messages, and will then receive them
from the broker
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Publish and Subscribe Example
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Request/Reply with Queues
• Correlation ID used to match request with corresponding
reply at the client
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Message Based Systems / MOM Products
•
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Canonical example: IBM MQSeries
(Sockets) – Berkeley Sockets
OpenJMS
Apache ActiveMQ (maintained by Fusesource)
IBM WebSphere MQ (IBMs MQSeries)
Amazon Simple Queue Service (SQS)
TIBCO TIBCO Rendezvous
Oracle Advanced Queuing
Microsoft Microsoft Message Queuing (MSMQ)
SUN Sun ONE Message Queue (JMS)
RabbitMQ
JBoss HornetQ
What is IBM WebSphere?
• WebSphere provides software for SOA environments
that enables dynamic, interconnected business
processes, and delivers highly effective application
infrastructures for all business situations.
• WebSphere is IBM's application and integration software
platform, and includes the entire middleware
infrastructure, including servers, services, and tools,
needed to create, deploy, run, and monitor round-theclock, enterprise-wide web applications and crossplatform, cross-product solutions.
https://www.ibm.com/developerworks/websphere/newt
o/
WebSphere MQ (IBM)
•
•
•
•
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•
Cross Platform
Dominant Messaging software – 70% of market
Messaging API same on all platforms
Guaranteed one-time delivery
Two-Phase Commit
Wide EAI industry support
MQ Series API (Basic)
•
•
•
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Connect to a Queue Manager
Open a queue
Put or get messages
Close a queue
Commit or roll back
Disconnect
MQ Series API (Advanced Features)
• Triggering – automatically starting an application
to process a message
• IMS and CICS Bridges – reusing legacy
transactions without modification
• Confirmation of message arrival, delivery
• Grouping of messages
• Load balancing
Local Queuing
Distributed Queuing
MQSeries
Distributed Queuing
MS Message Queue (MQ)
• Deployed in its Windows Server operating
systems since Windows NT 4 and Windows 95
• .NET: System.Messaging
• Create Queues via computer administration
– Queue name:
„Computername\private$\Queuename“
What is MSMQ?
• Message Queuing (MSMQ) technology enables
applications running at different times to
communicate across heterogeneous networks and
systems that may be temporarily offline.
• Applications send messages to queues and read
messages from queues. The following illustration
shows how a queue can hold messages that are
generated by multiple sending applications and read
by multiple receiving applications.
https://msdn.microsoft.com/enus/library/ms711472%28v=vs.85%29.aspx
MSMQ Features
•
•
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Point-to-point messaging
Persistent
Transactional
Trigger
Normal send/receive APIs
Very similar to IBM MQ Series
– Supports IP multicast as well…
MSMQ Queue Types
Application Queues
• Destination Queues
– Private
• ComputerName\private$\QueueName\
• private$\QueueName
– Public
• Response Queues
• Temporary / Local Queues
MSMQ Queue Types
Application Queues
• Destination Queues
– Private
• ComputerName\private$\QueueName\
• private$\QueueName
– Public
• Response Queues
• Temporary / Local Queues
System Queues
• Mediation Queues
• Dead Letter Queues
• Journal Queues
Amazon SQS
• Part of the AWS Cloud Computing Infrastructure
– Amazon Elastic Compute Cloud (Amazon EC2)
– Amazon Simple Storage Service (Amazon S3)
– Amazon Elastic BlockStore
– Amazon CloudFront
– Amazon SimpleDB
– …
– Amazon Simple Queue Service (Amazon SQS™)
Amazon SQS
Amazon SQS Features
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Multiple consumers and producers
Configurable Message Queues
Unlimited number of queues and messages
SOAP – APIs
Language support
– Java, PHP, Ruby, .NET
• At-Least-Once delivery
• No guarantee of message order
Amazon SQS Operations
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CreateQueue
ListQueues
DeleteQueue
SendMessage
ReceiveMessage
DeleteMessage
SetQueueAttributes
GetQueueAttributes
Amazon SQS
• Queues and Message Identifier
• – Queue URL
http://queue.amazonaws.com/123456790815/queue42
• – Message ID
• – Receipt Handler
MbZj6wDWli+JvwwJaBV+3dcjk2YW2vA3+STFFljTM8tJJg6
HRG6PYSasuWXPJB+Cw
Lj1FjgXUv1uSj1gUPAWV66FU/WeR4mq2OKpEGYWbnLm
pRCJVAyeMjeU5ZBdtcQ+QE
auMZc8ZRv37sIW2iJKq3M9MFx1YvV11A2x/KSbkJ0=
Amazon SQS
Amazon SQS
Java Message Service (JMS)
• Interface specification by Sun Microsystems to define
access to MOM
• Defines syntax and semantics
• First published in 1988
• Current specification: ???
• JMS supports:
– Point-to-Point
– Publish-and-Subscribe
– Request/Reply
Java Message Service (JMS)
• Two roles:
– JMS Provider = MOM Server = Queue Manger =
Message Broker
– JMS Client = Sender = Receiver
• Messages
• Administrative Objects published by the JMS provider
using JINI
– ConnectionFactory
– DestinationFactory
JMS Features
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Transacted sessions
Persistent/nonpersistent delivery
Durable / non durable subscriber
TTL
Message Priorities
Message selectors
SQL-like syntax to access header fields:
– subscriber = session.createSubscriber(topic, “priority > 6 AND
type = ‘alert’ ”);
• JMS can be used as a transport layer for SOAP
• Message Consumption
– Synchronously
– Asynchronously
JMS Example
JMS Example - HelloWorld
// Use JNDI to get ConnectionFactory and Queue
QueueConnectionFactory connectionFactory =
QueueConnectionFactory) ctx.lookup
("QueueConnectionFactory");
// Create connection and session
QueueConnection queueConnection
connectionFactory.createQueueConnection();
QueueSession queueSession
queueConnection.createQueueSession(...);
Queue queue = (Queue) ctx.lookup ("myQueue");
QueueSender sender = queueSession.createSender(queue);
// Create and send a message
Message message = queueSession.createTextMessage();
message.setText("Hello World");
queueSender.send(message);
Apache ActiveMQ
• Leading Open Source messaging platform
• Multi-Language Support
– Clients and Protocols from C, C++, C#, Ruby, Perl, Python, PHP
– Supported Java Standards: JMS 1.1, J2EE 1.4, JCA 1.5
• Multi-Protocol Support: TCP, NIO, UDP, SSL,
HTTP/S, STOMP
Apache ActiveMQ Features
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•
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Failover
High Availability
Clustering
Wide area deployment
Management
Security
Apache ActiveMQ: Failover
failover:(tcp://broker1:61616,tcp://broker2:6
1616,tcp://broker3:61616)?initialReconnectDela
y=100
failover://(tcp://masterhost:61616,tcp://slaveh
ost:61616)?randomize=false
Apache ActiveMQ: Synchronous
Consumer
public class MyConsumer {
...
public void doCreateConsumer() {
Destination destination =
consumer.getSession().createQueue("JOBS." + job);
MessageConsumer messageConsumer =
consumer.getSession().createConsumer(destination);
while ((message = consumer.receive(timeout)) !=
null)
{
processMessage(message);
}
}
Apache ActiveMQ: Asynchronous
Consumer
public class MyConsumer {
...
public void doCreateConsumer() {
Destination destination =
consumer.getSession().createQueue("JOBS." +
job);
MessageConsumer messageConsumer =
consumer.getSession().createConsumer(destination
);
messageConsumer.setMessageListener(new
MyMessageListener(job));
}
...
}
APPENDIX
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IBM MQSeries (1/3)
Basic concepts:
• Application-specific messages are put into, and removed from
queues
• Queues always reside under the regime of a queue manager
• Processes can put messages only in local queues, or through an
RPC mechanism
Message transfer:
• Messages are transferred between queues
• Message transfer between queues at different processes,
requires a channel
• At each endpoint of channel is a message channel agent (MCA)
– Setting up channels using lower-level network communication
facilities (e.g., TCP/IP)
– (Un)wrapping messages from/in transport-level packets
– Sending/receiving packets
IBM MQSeries (2/3)
• Channels are inherently unidirectional
• MQSeries provides mechanisms to automatically start MCAs
when messages arrive, or to have a receiver set up a channel
• Any network of queue managers can be created; routes are set
up manually (system administration)
IBM MQSeries (3/3)
Routing: By using logical names, in combination with name resolution to
local queues, it is possible to put a message in a remote queue
Question: What’s a major problem here?
Message Broker
Observation: Message queuing systems assume a common messaging protocol:
all applications agree on message format (i.e., structure and data
representation)
Message broker: Centralized component that takes care of application
heterogeneity in a message-queuing system:
• Transforms incoming messages to target format, possibly using
intermediate representation
• May provide subject-based routing capabilities
• Acts very much like an application gateway
IBM MQSeries
• One-to-one reliable message passing using queues
– Persistent and non-persistent messages
– Message priorities, message notification
• Queue Managers
– Responsible for queues
– Transfer messages from input to output queues
– Keep routing tables
• Message Channels
– Reliable connections between queue managers
• Messaging API:
MQopen
Open a queue
MQclose
Close a queue
MQput
Put message into opened queue
MQget
Get message from local queue
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Java Message Service (JMS)
• API specification to access MOM implementations
• Two modes of operation *specified*:
– Point-to-point
• one-to-one communication using queues
– Publish/Subscribe
• cf. Event-Based Middleware
•
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JMS Server implements JMS API
JMS Clients connect to JMS servers
Java objects can be serialised to JMS messages
A JMS interface has been provided for MQ
pub/sub (one-to-many) - just a specification?
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