Thursday, 14 August 2008

Lambda Expressions and Differentiation (continued)

Today, I made a presentation about the first article that I've posted on this blog. Since then I did some improvements on the code.

The one extra feature that I implemented was a parser for lambda expressions. One of the first things that I did when I started fiddling with lambda expression was trying to generate one from a string. To my disappointment, there's not such a feature included in the .NET Framework. So, I coded a humble one using CodeDom.

I'm sharing the last source code that I have. You're free to play with it with one condition. You have to share enhancements with me. :P

Also, I would like to let a challenge here. If you want to learn Lambda Expressions and don't have an idea to implement, try making code to simplify a polynomial function.

Finally, as always, please, let your comment here.

Friday, 8 August 2008

WebSphere MQ API (or MQAL)

WebSphere MQ (or simply "MQ") is a messaging system made by IBM. If you've never used any message-oriented middleware, it might be a good idea to take a look at wikipedia first. Anyway, the basic problems that I had to solve in the component I'm posting are not specific to MOM systems. Thus, I hope you can extract some value from it in any case.

So, let me introduce you to the problem. About one year ago, I had to develop an application that extensively uses MQ to exchange messages with other applications. This technology was kind of new to me and I had to learn the basics. To oversimplify, the idea is to connect to a queue manager, then connect to a queue, and finally put (or get) a message to (or from) the queue. The way that this process is made using the MQ API for .NET seemed very awkward to me. Then, I decided to write a component to encapsulate it and provide a simpler interface.

Fisrt, I've tried to find a design pattern to fit the component in and I choosed to follow the way that database connections are handled in the .NET framework. Then, I've started to make some analogies. To start, a queue manager connection could work pretty much like a database connection. Both of them have parameters like server, port, user name, password, and database name / queue manager name. To summarize, here are some of the analogies I've made:
- A queue manager is like a database;
- A queue manager connection is like a database connection;
- A queue manager connection parameters is like a database connection string;
- A queue is like a table (or a view);
- A queue connection is like an database command;
- A message is like a table row;
- A put message action is like an execute insert command;
- A get message action is like an execute select and delete command;
- A browse message action is like an execute select command.

Ok, you must have gotten the general idea. I won't get in much detail here, but let me list some of the problems I had to solve in order to implement this:
- Translating a queue connection string into queue manager connection parameters. I solved this by coding a connection string parser using regular expressions;
- Implement queue transactions. This wasn't a requisite at the time, but MQ provides transactions and I felt like I had to offer a way to use them;
- Inherently use a queue connection pool under the covers. The tests that I've made using the MQ API showed that it doesn't had a connection pool. I would had to either make the user of my component keep connections for longer (in order to avoid opening and closing them too frequently) or code a connection pool and let the user enjoy all its benefits. This was pretty interesting to do and probably deserves a post of itself. For now I'll let you with the source code.

By the way, I didn't touched this code for awhile now and I see that I've let some items on a TODO list, so I won't say it's a final version. Anyway, it's running in a production environment somewhere for months and it have not failed once.

Feel free to download the source code here.