Зависание программы из-за COM порта

int COMOpen(String portname)
{
 
 DCB dcb;
 COMMTIMEOUTS timeouts;
 String COMportNAME = " " + portname;
 
 COMport = CreateFile(AnsiString(COMportNAME.c_str()).c_str(),GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);
 
 if(COMport == INVALID_HANDLE_VALUE)
  {
 
   Form1->Memo1->Lines->Add("Com port can't open");
   return 1;
  }
 
if(!SetupComm(COMport, 2048, 2048)) {Form1->Memo1->Lines->Add("error (((");return 1; }
 
 dcb.DCBlength = sizeof(DCB);
 
 if(!GetCommState(COMport, &dcb))
  {
 
   COMClose();
 
String qq = "error DCB, "; qq +=String(GetLastError());
   Form1->Memo1->Lines->Add(qq);
   return 1;
  }
 
 dcb.BaudRate = 115200*20;//115200*28;  //115200*16; = 1843200 = 184'320 byte/s = 1'474'560 bit/s;
 dcb.fBinary = TRUE;
 dcb.fOutxCtsFlow = FALSE;
 dcb.fOutxDsrFlow = FALSE;
 dcb.fDtrControl = DTR_CONTROL_DISABLE;
 dcb.fDsrSensitivity = FALSE;
 dcb.fNull = FALSE;
 dcb.fRtsControl = RTS_CONTROL_DISABLE;
 dcb.fAbortOnError = FALSE;
 dcb.ByteSize = 8;
 dcb.Parity = 0;
 dcb.StopBits = 0;
 
 if(!SetCommState(COMport, &dcb))
  {
   COMClose();
   Form1->Memo1->Lines->Add("error DCB");
   return 1;
  }
 
 timeouts.ReadIntervalTimeout = 5000; //100; 
 timeouts.ReadTotalTimeoutMultiplier = 1000;//15;
 timeouts.ReadTotalTimeoutConstant = 5000;//100;
 timeouts.WriteTotalTimeoutMultiplier = 1000;//15; 
 timeouts.WriteTotalTimeoutConstant = 5000;//100; 
 
 if(!SetCommTimeouts(COMport, &timeouts))
  {
   COMClose();
   Form1->Memo1->Lines->Add("error");
   return 1;
  }
 
 SetupComm(COMport,2000,2000);
 PurgeComm(COMport, PURGE_RXCLEAR);
 
 reader = CreateThread(NULL, 0, ThreadRead, NULL, 0, NULL);
 return 0;
}

DWORD WINAPI ThreadRead(LPVOID lpParam)                                         //ThreadRead
{
 
 COMSTAT comstat;
 DWORD btr, temp, mask, signal;
 unsigned char bufrd_rez[1024];
 
 overlapped.hEvent = CreateEvent(NULL, true, true, NULL);
 SetCommMask(COMport, EV_RXCHAR);
 while(1)
  {
   WaitCommEvent(COMport, &mask, &overlapped);
   signal = WaitForSingleObject(overlapped.hEvent, INFINITE);
   if(signal == WAIT_OBJECT_0)
    {
     if(GetOverlappedResult(COMport, &overlapped, &temp, true))
      if((mask & EV_RXCHAR)!=0)
       {
        ClearCommError(COMport, &temp, &comstat);
        btr = comstat.cbInQue;
        if(btr)
        {
         ReadFile(COMport, bufrd_rez, btr, &temp, &overlapped);
 
          if (btr != 0) {
            DWORD cnt=0;
            for (cnt = 0; cnt < btr; cnt++) {
                        unsigned char RxDtat = (bufrd_rez[cnt]&0xFF);
 
            }
            }
        }
       }
    }
  }
 
}