I've mentioned Apache Qpid a number of times in this newsletter over the past year or so. In case you're not yet familiar with Apache Qpid, it's a message queuing system which implements the Advanced Message Queuing Protocol (AMQP). Because it's open source and freely available for multiple platforms, it's an attractive choice when you need reliable, persistent message queuing.

Apache Qpid offers client APIs in a number of languages, but I work more with the C++ version, so will use that language for this example.

To lay a little groundwork, the players in AMQP that we're concerned with are:

• Client: an entity that sends and receives messages. The example in this article is a client program.
• Exchange: destination for messages that a client sends; there are a number of different exchange types which provide various message distribution mechanisms such as direct, fan-out, and publish-subscribe (pub-sub).
• Queue: holds messages that a client will receive
  
• Broker: the traffic cop; manages exchanges, queues, and the routing between them
• Connection: a data connection to the broker
• Session: an abstraction for managing a set of message transfers; Sessions operate over Connections.
  

Our example will send a message to a direct exchange. The message will have a routing key that will help the broker route the message from the exchange to any queues that are interested in this message. A subsequent example will show how to receive such a message.

Ok, let's get into it... first, the header files we need:

#include <qpid/client/Connection.h>
#include <qpid/client/Session.h>
#include <qpid/client/Message.h>

In order to anything, we need a connection to the broker and a session to use. We'll assume there's a broker on the local system and that it's listening on TCP port 5672 (the default for Qpid).

qpid::client::Connection connection;
try {
  connection.open("localhost", 5672);
  qpid::client::Session session = connection.newSession();
  qpid::client::Message message("Hello, world!", "my_key");
  session.messageTransfer(arg::content=message, arg::destination="amq.direct");
  connection.close();
  return 0;
} catch(const std::exception& error) {
   std::cout << error.what() << std::endl;
  return 1;
}

That's it. Of course, there are many fancy options for when needed, but this program sends a message and will work on all Qpid platforms. If you're interested in checking out the API details behind this, the API reference is at http://qpid.apache.org/docs/api/cpp/html/index.html.

Keep an eye on my blog for more how-to article on Qpid (and ACE). Is there something particular you want to see an example of? Let me know!