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

.net performance pinvoke marshalling dllimport
Brian Scott picture Brian Scott · Apr 8, 2011 · Viewed 7k times · Source

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

Lee Berger picture Lee Berger · Apr 8, 2011

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.

Related questions

Best way to reverse a string

I've just had to write a string reverse function in C# 2.0 (i.e. LINQ not available) and came up with this: public string Reverse(string text) { char[] cArray = text.ToCharArray(); string reverse = String.Empty; for (int i = cArray.Length - 1; …

Read More
How to create a new object instance from a Type

One may not always know the Type of an object at compile-time, but may need to create an instance of the Type. How do you get a new object instance from a Type?

Read More
What's the fastest way to read a text file line-by-line?

I want to read a text file line by line. I wanted to know if I'm doing it as efficiently as possible within the .NET C# scope of things. This is what I'm trying so far: var filestream = new System.…

Read More