If you have to migrate an existing high performance application to Windows Azure, you will probably have highly optimized C and C++ code that takes advantage of multicore hardware and SIMD instructions. A long time ago, Windows Azure Mix 09 CTP introduced the ability to run Web and/or Worker Roles in full trust. The newest Windows Azure versions allow you to make P/Invoke (short for Platform Invoke) calls to invoke native code.

C++ code is very important in high performance computing. When you have to move compute-intensive algorithms to a Windows Azure cloud-based project, a Worker Role is usually an interesting option. However, there isn't a C++ Worker Role template in Windows Azure. You can choose between C#, Visual Basic and F#, and therefore, you have to work with managed code.

In "Multicore Programming Possibilities with Windows Azure SDK 1.3," I've already explained that you can use your parallelized algorithms that exploit modern multicore microprocessors in Windows Azure. If you have single-threaded or multi-threaded code in C++, you can reuse this code to create a C++ native assembly. Then, you must enable full trust support in Windows Azure and you will be able to invoke this native assembly by making a P/Invoke call. Remember that a P/Invoke call isn't free and it adds an overhead, and therefore, you have to consider the impact of this overhead.

It is easy to run a Web Role or a Worker Role in full trust. You just have to set the enableNativeCodeExecution flag in the service definition file to true. If a Web Role calls native code, you have to run it in full trust. You can check the documentation for the basic format of a service definition file containing a Web Role here. You can find the same information for a Worker Role here.

You can include the C++ code that builds the native assembly within the Azure solution, and then you can deploy it. Microsoft provides a very simple MSDN Virtual Lab "Windows Azure Native Code." The virtual lab teaches you to include a simple C++ native assembly in a Windows Azure solution, enable full trust, and then create a simple ASP.NET Website that calls the native assembly. If you don't want to run the virtual lab, you can download the lab manual, which includes step-by-step instructions to perform the aforementioned tasks with Visual Studio 2008.

You can follow these instructions in Visual Studio 2010 with Windows Azure SDK 1.3 and you will be able to run C++ code in your Azure solutions. The lab manual is very useful because you have to perform some complex steps and configurations that might confuse an expert developer. The lab manual includes screenshots and makes it really easy to build and deploy the Azure solution that calls native code. You can use this information to migrate C and C++ code to your cloud-based solutions that target Windows Azure.