Adapting a native code DLL to be called from a Store or Universal Windows app

Next, I kept getting DLLNotFound exceptions. OK, so you have to add the DLL as content in your C# project, and make sure it is set to copy to your output. I still got DLLNotFound exceptions. It turns out that you get this exception even when the DLL is present, if there is a dependency in the DLL which is not found. What dependency was not found? I downloaded the Sysinternals Process Monitor utility and set the filter to monitor my C# game. I excluded SUCCESS results. Then I tried to load the DLL. This told me that it was looking for the file msvcr120_app.dll (the Windows Runtime version of the Visual C++ runtime library). My first thought was to add runtime libraries from the appx deployment packages, in:

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.1\ExtensionSDKs\Microsoft.VCLibs\12.0


Then I discovered that all you need to do is to add a reference to the Visual C++ runtime packages, much easier. That fixed DLLNotFound.

Next, I had some problems calling the 64-bit DLL with Platform Invoke (PInvoke) from C#. I found it easier to compile both my C# app and the DLL itself as 32-bit code. I may go back to the 64-bit option later.

Concurrency issues

Now I had everything working; except that my DDS port was far inferior to the standard one because it was single-threaded. The original used QueueUserWorkItem which is not available in a Windows Runtime DLL. I searched for what to do, and came across this MSDN article which recommends using RunAsync, WorkItemHandler and IAsyncAction. However my DLL was not currently compiled using /ZW for “Consume Windows Runtime Extension”. I could add that of course; but then my DLL would have a dependency on the Windows Runtime and if I wanted to use the code for, say, Windows 7, it would not work. or not without yet more #ifdef blocks. No big deal perhaps; but my preference was to avoid this dependency.

There may be other solutions, but the one that I found was to use the Concurrency Runtime. Previously, QueueUserWorkItem was called in a for loop. I simply modified this to use a parallel_for loop instead, using the example here for guidance. I also added:

#include <ppltasks.h>

using namespace concurrency;

to the top of the code. It works well, speeding performance by about three times on my quad-core desktop. Of course I was greatly helped by the fact that the code was already written with concurrency in mind.


The effect is spoiled by the time it takes to load the DLL but fortunately you can get DDS to solve multiple boards in one call though I have yet to experiment with this.

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