Saturday 29 January 2011

Strawberries and a Python through the Looking Glass

How do we get OpenPGM on Windows?  This is an obvious question popular with new developers.  The stumbling blocks tend to be that OpenPGM is written to the ANSI C99 specification and Microsoft's Visual C++ 2010 compiler only supports ANSI C89 or C++ 2003.

Convexing Cross-Compiling of C

Microsoft hasn't the only C compiler vendor targeting Windows, and it also isn't necessary that the compiler actually runs on Windows, by a process called cross-compiling the Windows platform can be targeted from another.  This also tends to be scary for many Windows developers as they need a second operating system, learn how to use a new compiler, and finally you have additional compiler dependencies when bringing back the library on Windows.

Priceless Princely Patch for Progress

As it so happens cross-compilation has its pros and cons, on the plus side it means one code base and one build system; on the negative side it means the resultant library brings in additional libraries for the cross-compiler and its compatibility layers, and debugging is made rather inconvenient.

So the benefits of a native build are strong but how much effort is required to modify C99 code to get it working in a C89 compiler and how difficult is a native build system?  Well the differences from one compiler to the next can be managed with a patch cluster.  The build system is similar to Automake and SConscript build components as the Autoconf comparables are constant to Windows XP SP3.  We choose a build system that can target agnostic to Visual Studio compiler version for greatest compatibility to minimize maintenance overhead.

CMake Make Make

With Microsoft Visual C++ 2010 installed we need to install some extra software to start, first the build system called CMake which has a simple Win32 installer with minimal options, it is recommended to allow it to update your system PATH so you can use immediately.  Next are two critical build dependencies for OpenPGM, we need both the Perl and Python 2 scripting languages both of which offer x86 and x64 builds depending on your platform architecture.

Extract the source for the latest OpenPGM archive into somewhere convenient, for example C:\>

CMake generating Makefile.
By default CMake is creating a Makefile with debugging enabled, you can use cmake-gui to update the parameter for a release build.

CMake-GUI updating configuration parameters and regenerating Makefile.
With a successfully generated Makefile we can start the build process using Microsoft's standard command line tools.

Generating C89-compatible source files.
The build process continues automatically by first patching all the source files for C89 compatibility,  the C89-compatible source files are fed into the compiler, finally the object files are linked together into the native library.

Generating object files and final libpgm library.
Now complete we can start to use the library to build the example applications and start development.  An additional feature of the CMake system is called CPack which allows us to create a Windows installer we can use to install OpenPGM binaries on other systems.

First download the latest NSIS package and install with full options, then simply run cmake package to produce the Windows installer.

Building an OpenPGM Windows installer with CPack and NSIS.

What is PGM? What is OpenPGM?

Well lets start by saying PGM is the name of a internet, lower-case "i", communications protocol, and OpenPGM is an implementation of that protocol.  A communications protocol being the definition of how two or more computers or electronic devices communicate with each other.  For example you just enjoyed a good slice of cherry pie and damn fine cup of coffee and you wanted to tweet it to your friends, you tap the message into your phone and hit a button, then by magic the message appears on your microblog.  Between your phone's Twitter app' and the Twitter website your tweet message has been sent following a predefined communications protocol.

There is a subtle difference between the Internet, upper-case "I", and an internet, lower-case "i", the former is the name for the public network where we can access Facebook and Twitter, the latter is the generic term for a group of interconnected networks.  This means we could find PGM on the Internet or we could find it on other non-public networks such as within a stock exchange's trading system or communicating physics of the Higgs Boson at the Large Hadron Collider.

So what is special about PGM?

The erhu is a Chinese two-stringed bowed musical instrument and not commonly found in Western music.  If you wanted to listen to a recital of Sanmen Capriccio a convenient choice might be to watch a performance by Yang Ying on YouTube.  For a live performance you might tune in the radio and listen alongside other fans of huqin.  On the Internet you may find an Internet radio station to listen on but there is fundamental limitation on how many fans can be plugging in.  Say Girls Generation announced a online concert tonight the stampede from eager fans may overload the site and crash the network as the concert site has to stream a duplicate copy of the event to each and every listener.  The PGM protocol allows one sent stream of data to be received by multiple recipients, the fan-out of the stream to each recipient being managed by the network instead of say the host concert site.

Why should I choose OpenPGM?

So PGM is the protocol on paper, digitally at least, you need an actual implementation for something to start looking like it will work.  There are a selection of vendors providing commercial solutions, including Microsoft, IBM, and TIBCO,  and a variety of open source projects as long as your preferred platform is FreeBSD.  So an open source implementation that works on multiple platforms, is compatible with existing vendor solutions, and is even faster and more flexible sounds like a good choice, then have a look at OpenPGM.