Archive for the ‘CodeProject’ Category

TCP/IP Parameter Tuning for Rapid Client Connections

Wednesday, February 17th, 2010

Applications that open and close a large number of client TCP/IP sockets run the risk of running out of available socket ports.  This can happen in a load and performance testing scenario using a tool like LISA Test from iTKO, or it could happen in a production environment if an active application simply needs to rapidly open and close a large number of outbound connections.

On the .NET platform, the exception raised reads “System.Net.Sockets.SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted <host>:<port>“. 

In Java, the exception is “java.net.BindException: Address already in use: connect“. 

Both exceptions are misleading because they are generally associated with server socket conflicts – not outbound client socket connections.  However, a better understanding of the TCP state machine sheds some light on this behavior – and a solution.

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The .NET Asynchronous I/O Design Pattern

Thursday, February 11th, 2010

Asynchronous operations allow a program to perform time consuming tasks on a background thread while the main application continues to execute.  For example, consider when a program makes a request to a remote system.  In a single-threaded scenario, the call is made and the CPU goes idle as the caller waits on the server’s processing time and the network latency.  If this waiting time can be delegated to a separate thread of execution, the program can complete other tasks until it receives notification the background work is complete.

However, managing multiple threads and cross-thread communication adds complexity to your code.  Fortunately, the .NET Framework has a useful design pattern applied to its I/O classes which easily enables asynchronous calls.  Let’s take a look at an example.

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Understanding SSL – Part 1: Certificates and Keys

Wednesday, October 14th, 2009

The technology behind Secure Sockets Layer (SSL) network connections is often perceived as a bit of “black magic” – smoke and mirrors securing our Internet connections from snooping.  When banking and shopping online, even a novice user understands their browser sets up an HTTPS connection (which is simply HTTP over SSL) to protect the transaction.  It’s easy to simply surf to a secure URL and know that, somehow, SSL is magically keeping you safe.

Developing software that uses SSL is an entirely different matter.  The simplicity quickly fades, and the developer must confront the complexities of certificate management, trust stores, handshaking, and a host of other details that must be perfectly aligned to make the secure communication work.  In Part 1, we’ll cover a very high level of SSL concepts.  In subsequent posts, we’ll take a deeper dive into making these connections happen in both Java and C#.

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C# Decimal and Java BigDecimal Solve Roundoff Problems

Tuesday, November 6th, 2007

Roundoff problems have been the bane of programmers since computers started handling floating point numbers. Floating point numbers are represented by a finite number of bytes. This limits the precision of numbers that may be represented – you only get so many significant digits. More subtly, however, finite length floating point numbers limit which numbers may be represented accurately. Repeating decimals (which, in a sense, require an infinite number of significant digits) cannot be represented precisely. You may only store the nearest value representable by the computer. This is the origin of annoying roundoff problems found in floating point arithmetic.

The C# and Java 4-byte float data type provides 7 significant digits of precision, while the 8-byte double type provides 15. Using the higher precision double data type helps minimize the roundoff error, but it must still be addressed.

So, when I encountered the C# 12-byte decimal data type with its 28 significant digits, and Java’s arbitrary size BigDecimal data type, I figured these were simply ways of further minimizing the problem with a wider floating point type. Only after digging deeper did I realize that the implementation behind both of these data types is a stroke of genius.

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NHibernate in a Medium Trust Environment

Tuesday, August 21st, 2007

I’ve recently started experimenting with NHibernate – the C#/.NET version of the Hibernate O/R matpping tool that was originally developed for Java. The Java version is very powerful, and I’m a huge fan of it. The C#/.NET version is, for the most part, a straight port of the Java code base (and an ugly port, in some ways). Nevertheless, it appears to be just as robust as its predecessor.

Be warned, however, that the NHibernate DLLs require a high level of trust in the ASP.NET environment they’re deployed to. I spent an entire weekend beating my head against a wall trying to get a simple app up on my GoDaddy account. I suspect NHibernate probably wasn’t designed with a medium trust environment in mind. I was able to make a few tweaks to get the code running with fewer permissions requirements. However, the permissions required to enable dynamic proxies – a fundamental part of the NHibernate architecture – are non-negotiable.

I learned from GoDaddy tech support that their Deluxe Windows plan, a shared host environment, simply doesn’t allow those permissions. I’d need to upgrade to a dedicated server, and that’s just a little too pricey for an environment simply for experimentation. I was able to get NHibernate working without any hacks at Webhost4life, but I thought I’d share what I tried first at GoDaddy just to help you understand the permissions implications if you’re in a medium trust environment — and how you might need to address them on your own projects.


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C#, GPS Receivers, and Geocaching: Vincenty’s Formula

Monday, August 6th, 2007

Vincenty’s Formula is an iterative solution for calculating the distance and direction between two points along the surface of Earth. For clarity, I’ve stripped out portions of the code I’ve put up for discussion, but you can download the entire C# source code from here. If you prefer Java, please see the Java version of this discussion.

Several years ago, I stumbled on a great pastime called “geocaching.” It’s a worldwide treasure hunting game where participants use handheld GPS receivers to find hidden “caches” – small boxes filled with prizes, trinkets, and “travel bugs“. The caches are hidden by other participants who post nothing more than the latitude and longitude on a website like Geocaching.com. My children and I have had a blast. It’s a great way for a grown man to justify playing in the woods (and buying an expensive gadget!) under the pretense of “playing with the kids.” With over 420,000 caches in 222 countries on all continents (including Antarctica!) there are bound to be several near you.

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C# Grief With Overloaded Operators

Tuesday, July 31st, 2007

Here’s a nasty bug that crept into one of my team’s projects recently. When will equivalent C# objects fail to compare as equal? The answer is “when operator== doesn’t work as expected.”

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Intercepting Add and Remove of C# Event Delegates

Wednesday, July 25th, 2007

All you geniuses and rocket scientists out there probably already know this, but I just stumbled on it, and I think it’s kind of cool. Did you know you can customize the adding and removing of C# event handlers? I didn’t.

I’m going to end this post with the question “Yes, but what’s it good for?” You folks with the Ph. D. in C#, feel free to scroll to the bottom and post your answers. For my fellow mortals out there, let me recap what I’m talking about.

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