Is there generally a noticeable performance hit when calling PInvoke on Win32 / COM methods?

Question

I'm wondering whether anyone has a decent explanation or overview on the negative aspects of using DLLImport / PInvoke on Win32 methods from managed .Net code?

I plan to make use of various Win32 methods and would like to have a greater understanding on the negative implications of doing so.

Thanks,

Brian.

Answer 1

According to MSDN - Calling Native Functions from Managed Code

PInvoke has an overhead of between 10 and 30 x86 instructions per call. In addition to this fixed cost, marshaling creates additional overhead. There is no marshaling cost between blittable types that have the same representation in managed and unmanaged code. For example, there is no cost to translate between int and Int32.

In my experience, there definitely is an overhead when P/Invoking native functions, but usually the performance hit isn't worth worrying about. The marshaling cost is something to keep in mind. If you are passing in large structures, strings, etc. then the performance costs will quickly show.

For P/Invoked functions that are called very frequently, you may want to consider adding [SuppressUnmanagedCodeSecurity] to your P/Invoke function definitions (see MSDN - SuppressUnmanagedCodeSecurityAttribute). This stops the runtime from doing a stack walk to ensure the caller has UnmanagedCode permission. Of course, make sure you understand the security ramifications before adding this attribute.