Re: thread related issue

hi all,
i am having one problem with threading

i created one dialog based application whose work is to read the data
from serial port and display it.so i created one thred for this work.

means now i got two threads one is application thread and other is
serial communication thread which is created in OnInitDialog.

now everything is working i mean the thread got created it read some
bytes
from port and now it wants to show the data so need to send this data
to main
thread. so i am doing this with ::SendMessage() but it is giving access
violation. i don't know why this is happening and currently i am not
sending the data also i.e. buffer so please help me
below is code (stepwise)

1)In Oninitdialog
THREADPARAM *ptp = new THREADPARAM;
       if(ptp)
       {
           memset(ptp->array,0,30);
           strcpy(ptp->array,"Harshal");
           ptp->appHandle = this->m_hWnd;
           hSerialThread = CreateThread( NULL,

                                   0,
                                   (LPTHREAD_START_ROUTINE)
SerialCommunication,

                                   (LPVOID) NULL,

                                   0,
                                   &dwSerialThreadID);
       }

2)Thread function
UINT SerialCommunication(LPVOID pParam)

{
   int write_req=0;
   THREADPARAM *ptp = (THREADPARAM *)pParam;
   while(1)
   {
       if(write_req == 2)// send write request and read it
       {
           DWORD length=0;
           DWORD dwRead=0;
           if (WriteFile(hCom,
                 SEND_CMD, // pointer to data to write to
file
                 NOOFBYTE, // number of bytes to write
                 &length, // pointer to number of bytes
written
                 NULL) == 0)
           {// write failed
               write_req = 0;
               continue;
           }
           // writefile succeeded issue readfile
           char buffer[MAX_MESSAGE];
               memset(buffer,0,MAX_MESSAGE);
               if (!ReadFile(hCom, buffer, MAX_MESSAGE, &dwRead,
NULL))
               {
                   write_req = 0;
                   continue;
               }
               if(dwRead > 0)
               {
                   //MessageBox(NULL,buffer,"Data with packet",MB_OK);

                   ::SendMessage(ptp->appHandle,MY_SHOW_DATA,0,0);//
error is here

3) Sent message function

LRESULT CReadDataDlg::OnShowDataMessage(UINT wParam, LONG lParam)