Access Unity Script Function From External Program

Hello,

I've been trying to create a simple, external C++ program that executes a specific script function in Unity. Using various example found on the forums, I started by creating a native plugin (c++ dll) and I'm able to execute a function in the plugin from Unity, but the only way I've been able to execute a Unity script function from the plugin is if Unity initiates the function call. I'll post the code, hopefully you can see what I'm doing:

.dll header

 #pragma once
 
 #if TESTDLL_EXPORTS
     #define API extern "C" __declspec(dllexport) 
 #else 
     #define API extern "C" __declspec(dllimport) 
 #endif
 
 typedef void(__stdcall* UnitySendMessageFunc)(const char* gameObjectName, const char* methodName, const char* message);
 UnitySendMessageFunc UnitySendMessage;
 
 API void __stdcall SetUnitySendMessageCallback(UnitySendMessageFunc sendMessageCallback);
 
 API int test();
 
 typedef int(__stdcall *ANSWERCB)();
 static ANSWERCB cb;
 API void TakesCallback(ANSWERCB fp);

.dll cpp:

 //UnitySendMessage = nullptr;
 
 API void __stdcall SetUnitySendMessageCallback(UnitySendMessageFunc sendMessageCallback)
 {
     UnitySendMessage = sendMessageCallback;
 }
 
 API int test()
 {
     std::cout << "test";
     return 34;
 }
 
 API void TakesCallback(ANSWERCB fp)
 {
     UnitySendMessage("Sphere", "CallTest", "123456789"); //This only works if Unity calls TakesCallback
     cb = fp;
 }

Here is the Test.cpp that is to execute the Unity Function:

 #include "stdafx.h"
 #include "testdll.h"
 #include <iostream>
 #include <future>
 #include <windows.h>
 //#pragma comment (lib,"testdll.lib")
 
 int main()
 {
     while (true)
     {
         std::this_thread::sleep_for(std::chrono::milliseconds(3000));
         std::cout << clock() / 1000 << " seconds have passed" << std::endl;
 
         UnitySendMessage("Sphere", "CallTest", "123456789"); //This Creates the Access Violation error/crash
         //TakesCallback(cb);
 
         //std::cout << test();
     }
 
     return 0;
 }

And finally the Unity Script:

 public class UnityPlugin2 : MonoBehaviour
 {
     public delegate int myCallbackDelegate();
 
     int myCallback()
     {
         return 234;
     }
 
     public delegate void UnitySendMessageDelegate([MarshalAs(UnmanagedType.LPStr)]string gameObjectName, [MarshalAs(UnmanagedType.LPStr)]string methodName, [MarshalAs(UnmanagedType.LPStr)]string message);
 
     private static UnitySendMessageDelegate s_SendMessageDelegate;
 
     [DllImport("testdll")]
     private static extern void SetUnitySendMessageCallback(UnitySendMessageDelegate sendMessage);
     [DllImport("testdll")]
     private static extern void TakesCallback(myCallbackDelegate fp);
 
     // Use this for initialization
     void Start ()
     {
         s_SendMessageDelegate = UnitySendMessageWrapper;
         SetUnitySendMessageCallback(s_SendMessageDelegate);
 
 
         TakesCallback(new myCallbackDelegate(this.myCallback));
 
 
         System.Diagnostics.Process.Start("C:\\Users\\vferguson\\Downloads\\UnityPlugin-master\\UnityPluginTest\\Assets\\Plugins\\Test.exe");
     }
 
     private static void UnitySendMessageWrapper(string gameObjectName, string methodName, string message)
     {
         Debug.Log("This Happend"); //This should always get hit when message comes through
         var gameObject = GameObject.Find(gameObjectName);
         if (gameObject != null)
         {
             //gameObject.SendMessage(methodName, message);
         }
     }
 
     void Awake()
     {
 
     }
 
     // Update is called once per frame
     void Update ()
     {
     
     }
 }

The test.cpp program will crash at "UnitySendMessage", but when Unity calls "TakesCallback" then "UnitySendMessage" works like its suppose to. I might be going about doing this all wrong, any help would be appreciated.

Thanks