How to get a HANDLE from a ActiveX with ATL

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ATL

I am developing an ActiveX with vs2008 (ATL9.0) project, the ActiveX didn't contain any form or control. I want to send a message from a subprocess to the main process by postmessage or sendmessage, but the function needs a handle for the main process. I want to get the main process handle and I use hCurrModul=GetModuleHandle(NULL);function to process, but get the value is invalid to possmessage.
My base code :
Add the message map
xxxxctrl.h

#define WM_GETUII WM_APP+101 //operate success
.
.
BEGIN_MSG_MAP(CRMU9xCtrl)
      MESSAGE_HANDLER(WM_GETUII, OnGetUiiResult)
END_MSG_MAP()

.
.
Subprocess function:

unsigned int __stdcall CRMU9xCtrl::threadReadUii(void * pThis)//
{
 for(int i=0;i<1000,i++)
 { 
    .....

 }
    HWND hwndMain =(HWND)pThis;  
    ::SendMessage(hwndMain,WM_GETUII,(WPARAM)0,sendMsg);
}

Main process begin thread:

STDMETHODIMP CRMU9xCtrl::_RMUConnect(BSTR sPort, BYTE crcFlag, LONG* hCom)
{
 ...
hthread=(HANDLE)_beginthreadex(NULL, 0, &CRMU9xCtrl::threadReadUii, (LPVOID)this, 0, &threadID );
...
}

Message maping function:

OnGetUiiResult(UINT /*uMsg*/,WPARAM wParam, LPARAM lParam,BOOL& /*bHandled*/)
{
    this->Fire_onGetUii(tmp);
    return 0;
}