Why do I get a \'pinvokestackimbalance\' Exception in Visual Studio 2010?

PinvokeStackImbalance Exception: Understanding and Resolution in Visual Studio 2010

In Visual Studio 2010, certain calls to C DLLs may result in a "pinvokestackimbalance" exception. This exception was disabled by default in Visual Studio 2008, but is enabled by default in Visual Studio 2010.

Cause of the Exception

The "pinvokestackimbalance" exception is not actually an exception but a managed debugging assistant (MDA). It detects inconsistencies in the calling convention between managed and unmanaged code when using platform invoke (P/Invoke).

Incorrect Calling Convention

In the provided code example, the C# code uses the [DllImport] attribute with the default CallingConvention.WinApi, which is equivalent to CallingConvention.StdCall for x86 desktop code. However, the C code uses the __cdecl calling convention.

Resolution

To resolve this issue, the CallingConvention attribute in the [DllImport] attribute must be explicitly set to CallingConvention.Cdecl to match the calling convention used in the C code. The updated code would look like:

<code class="csharp">[DllImport("ImageOperations.dll", CallingConvention = CallingConvention.Cdecl)]
static extern void FasterFunction(
    [MarshalAs(UnmanagedType.LPArray)] ushort[] inImage, 
    [MarshalAs(UnmanagedType.LPArray)] byte[] outImage, 
    int inTotalSize, int inWindow, int inLevel);</code>

Additional Note

The "pinvokestackimbalance" MDA is only active in debug mode. In release mode, it will not trigger the exception. Therefore, if the issue is only occurring in debug mode, setting the CallingConvention attribute correctly should resolve it.

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