dll not found exception when c++ methods are call from multiple threads

I have tried creating a simple c++ dll which has only few methods. I noticed that some very simple methods (which does not involve pointers) work fine in multi-threading with unity.

However when I call a method which creates a new Int and then call another method which deletes this Int (in c++), this throws exception under multi threading.

I am posting this sample code.

c++ methods:

 // simpledll.cpp : Defines the exported functions for the DLL application.
 //
 
 #include "stdafx.h"
 #include <vector>
 #ifdef __cplusplus
 extern "C" 
 #endif
 __declspec(dllexport) float __stdcall  blankfloat()
 {
     return (5) ;
 }
 #ifdef __cplusplus
 extern "C" 
 #endif
 __declspec(dllexport) void* __stdcall  blankpointer()
 {
     return (void*)(NULL) ;
 }
 #ifdef __cplusplus
 extern "C" 
 #endif
 __declspec(dllexport) void* __stdcall  createIntPointer()
 {
     return (void*)(new int()) ;
 }
 #ifdef __cplusplus
 extern "C" 
 #endif
 __declspec(dllexport) void __stdcall  deleteIntPointer(void* intPtr)
 {
     delete (int*)intPtr;
 }

c# code: using UnityEngine; using System.Collections.Generic; using System.Threading; using System; using System.IO; using System.Runtime.InteropServices;

 public class $$anonymous$$ultiThreadTest : $$anonymous$$onoBehaviour {
     
     [DllImport ("simpledll", EntryPoint="blankpointer")]
     private static extern IntPtr blankpointer ();
     
     [DllImport ("simpledll", EntryPoint="blankfloat")]
     private static extern float blankfloat ();
     
     [DllImport ("simpledll", EntryPoint="createIntPointer")]
     private static extern IntPtr createIntPointer ();
     
     [DllImport ("simpledll", EntryPoint="deleteIntPointer")]
     private static extern void deleteIntPointer (IntPtr ptr);
     
     List<Thread> threadList = new List<Thread>();
     bool alive = true;
     int numOfThreads = 2; 
     
     StreamWriter file;
     // Use this for initialization
     void Start () {
         
         file = new StreamWriter(Application.strea$$anonymous$$gAssetsPath + "/threadlog.log");
         file.AutoFlush = true;
         
         print(blankfloat().ToString());
         
         for(int i = 0; i < numOfThreads; i++)
         {
             Thread newThread =  new Thread(new ThreadStart(ReadThreaded));
             
             threadList.Add(newThread);
             
             newThread.Start();
         }
     }
     
     void ReadThreaded()
     {
         while(alive)
         {
             try
             {
                 
                 IntPtr ptr = createIntPointer();
         
                 
                 
                 deleteIntPointer(ptr);
                 
             }
             catch(Exception exp)
             {
                 lock(this)
                 {
                     file.WriteLine("Exception $$anonymous$$essage: " + exp.$$anonymous$$essage);
                     
                     if(exp.GetBaseException() != null)
                     {
                         file.WriteLine("Base Exception: " + exp.GetBaseException().$$anonymous$$essage);
                     }
                     if(exp.InnerException != null)
                     {
                         file.WriteLine("Inner Exception: " + exp.InnerException.$$anonymous$$essage);
                     }
                 }
             }
         }
     }
     // Update is called once per frame
     void Update () {
     
     }
             
     void OnDestroy()
     {
         alive = false;
         foreach(Thread t in threadList)
         {
             t.Join();
         }
                 
         threadList.Clear();
     }
 }
 

Just to add, I used the above c++ dll code in a Visual C# (.net) project. I was able to run 20 parallel threads with no exceptions at all.

I am not using any Unity functionality in the above threads. This makes me think whether this problem is related to $$anonymous$$ono.