sendarp with multithreading function is not working for whole subnet (wifi environment)

I was trying to fetch Mac addrs of all the devices present in WiFi environment(whole subnet).

Initially when i ran the code approx it took 10 mins to get the result for whole subnet so in order to reduce the time i used multithreaded concept in windows machine but this method is not at all working.

I am pasting the code snippet below. Even i tried different logic like running 255, 100, 50 ,2 threads at a time but still it failed.

I suspect synchronization issue in this but i don't have any idea to resolve this, so please help me in this getting done.

DWORD WINAPI GetMacAddrOfSubNet(LPVOID lpParam)
{

   DWORD dwRetVal;
   IPAddr DestIp = 0;
   IPAddr SrcIp = 0;       /* default for src ip */
   ULONG MacAddr[2];       /* for 6-byte hardware addresses */
   ULONG PhysAddrLen = 6;  /* default to length of six bytes */
   char look[100];

   strcpy(look ,(char *)lpParam);
   DestIp = inet_addr(look);

   memset(&MacAddr, 0xff, sizeof (MacAddr)); 
   /*Pinging particular ip and retrning mac addrs if response is thr*/
   dwRetVal = SendARP(DestIp, SrcIp, &MacAddr, &PhysAddrLen);
   if (dwRetVal == NO_ERROR) 
   {
       /**/ 
   } 
   return 0;
}

extern "C" __declspec(dllexport) int __cdecl PopulateARPTable(char *IpSubNetMask)
{

   char ipn[100];
   char buffer[10];
   unsigned int k;
   DWORD   dwThreadIdArray[260];
   HANDLE  hThreadArray[260]; 

   /*Run 255 threads at once*/
   for (k=1; k<255; k++)
   {
       itoa(k, buffer, 10);
       strcpy(ipn, IpSubNetMask);
       strcat(ipn, "."); 
       strcat(ipn, buffer);

       /*Thread creation */
       hThreadArray[k] = CreateThread( NULL, 0, GetMacAddrOfSubNet, ipn, 0, &dwThreadIdArray[k]);
       if (hThreadArray[k] == NULL) 
       {           
          //ExitProcess(3);
       }
   }
   WaitForMultipleObjects(255, hThreadArray, TRUE, INFINITE);

   return 0;

}

The ipn buffer only exists once. You are using and modifying it as parameter for your (up to) 255 threads. And you expect that the statement strcpy(look ,(char *)lpParam) in the thread will be performed before the main thread modifies ipnagain for calling the next thread. But this is not the case, at least it's not guaranteed. So your threads may use wrong parameters.

Either use different buffers for each thread, or implement a synchronization, that ensures that the parameter has been copied by the thread before main thread modifies the buffer again.

sendarp with multithreading function is not working for whole subnet (wifi environment)

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