Playing with the .NET JIT Part 3

Integrating unmanaged code into the managed platform is one of the problem areas with the managed world. Often times the exact costs of calling into unmanaged code is unknown. This obviously leads to some confusion as to when it is appropriate to mix in unmanaged code to help to improve the performance of our application.

PInvoke

There are three ways to access an unmanaged function from managed code. The first is to use the PInvoke capabilities of the language. In C# this is done by declaring a method with external linkage and indicating (using the DllImportAttribute attribute) in which DLL the method may be found. The second way would be to obtain a pointer to the function (using LoadLibrary/GetProcAddress/FreeLibrary), and marshal that pointer to a managed delegate using Marshal.GetDelegateForFunctionPointer. Finally you can write an unmanaged wrapper around the function, using C++/CLI, and invoke that managed method, which will in turn call the unmanaged method.

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