[CONF] Apache Qpid: QMF Python Console Tutorial (page edited)

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Page Edited : qpid : QMF Python Console Tutorial QMF Python Console Tutorial has been edited by Ted Ross (Jan 28, 2009). (View changes) Content: Prerequisite - Install Qpid Messaging Synchronous Console Operations Creating a QMF Console Session and Attaching to a Broker Accessing Managed Objects Viewing Properties and Statistics of an Object Invoking Methods on an Object Asynchronous Console Operations Discovering what Kinds of Objects are Available Prerequisite - Install Qpid Messaging QMF uses Qpid Messaging as its means of communication. To use QMF, Qpid messaging must be installed somewhere in the network. Qpid can be downloaded as source from Apache, is packaged with a number of Linux distributions, and can be purchased from commercial vendors that use Qpid. Please see Download for information as to where to get Qpid Messaging. Qpid Messaging includes a message broker (qpidd) which typically runs as a daemon on a system. It also includes client bindings in various programming languages. The Python-language client library includes the QMF console libraries needed for this tutorial. Please note that Qpid Messaging has two broker implementations. One is implemented in C++ and the other in Java. At press time, QMF is supported only by the C++ broker. If the goal is to get the tutorial examples up and running as quickly as possible, all of the Qpid components can be installed on a single system (even a laptop). For more realistic deployments, the broker can be deployed on a server and the client/QMF libraries installed on other systems. Synchronous Console Operations The Python console API for QMF can be used in a synchronous style, an asynchronous style, or a combination of both. Synchronous operations are conceptually simple and are well suited for user-interactive tasks. All operations are performed in the context of a Python function call. If communication over the message bus is required to complete an operation, the function call blocks and waits for the expected result (or timeout failure) before returning control to the caller. Creating a QMF Console Session and Attaching to a Broker For the purposes of this tutorial, code examples will be shown as they are entered in an interactive python session. $ python Python 2.5.2 (r252:60911, Sep 30 2008, 15:41:38) [GCC 4.3.2 20080917 (Red Hat 4.3.2-4)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> We will begin by importing the required libraries. If the Python client is properly installed, these libraries will be found normally by the Python interpreter. >>> from qmf.console import Session We must now create a Session object to manage this QMF console session. >>> sess = Session() If no arguments are supplied to the creation of Session, it defaults to synchronous-only operation. It also defaults to user-management of connections. More on this in a moment. We will now establish a connection to the messaging broker. If the broker daemon is running on the local host, simply use the following: >>> broker = sess.addBroker() If the messaging broker is on a remote host, supply the URL to the broker in the addBroker function call. Here's how to connect to a local broker using the URL. >>> broker = sess.addBroker("amqp://localhost") The call to addBroker is synchronous and will return only after the connection has been successfully established or has failed. If a failure occurs, addBroker will raise an exception that can be handled by the console script. >>> try: ... broker = sess.addBroker("amqp://localhost:1000") ... except: ... print "Connection Failed" ... Connection Failed >>> This operation fails because there is no Qpid Messaging broker listening on port 1000 (the default port for qpidd is 5672). If preferred, the QMF session can manage the connection for you. In this case, addBroker returns immediately and the session attempts to establish the connection in the background. This will be covered in detail in the section on asynchronous operations. Accessing Managed Objects The Python console API provides access to remotely managed objects via a proxy model. The API gives the client an object that serves as a proxy representing the "real" object being managed on the agent application. Operations performed on the proxy result in the same operations on the real object. The following examples assume prior knowledge of the kinds of objects that are actually available to be managed. There is a section later in this tutorial that describes how to discover what is manageable on the QMF bus. Proxy objects are obtained by calling the Session.getObjects function. To illustrate, we'll get a list of objects representing queues in the message broker itself. >>> queues = sess.getObjects(_class="queue", _package="org.apache.qpid.broker") queues is an array of proxy objects representing real queues on the message broker. A proxy object can be printed to display a description of the object. >>> for q in queues: ... print q ... org.apache.qpid.broker:queue[0-1537-1-0-58] 0-0-1-0-1152921504606846979:reply-localhost.localdomain.32004 org.apache.qpid.broker:queue[0-1537-1-0-61] 0-0-1-0-1152921504606846979:topic-localhost.localdomain.32004 >>> Viewing Properties and Statistics of an Object Invoking Methods on an Object Asynchronous Console Operations Discovering what Kinds of Objects are Available

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