Starting a timer from a worker thread

Hi,

I'm using a worker thread to call a time consuming function (tcf) in a dll
and want to use a timer to update a progress bar on my dialog. The dll
provides a percent complete function, which appears to throw an error if
called at an inappropriate time (i.e. outside the scope of the tcf).

In order to reduce the risk of this error being encountered I want to start
the timer in the worker thread immediately before the call and stop it
immediately after. My interval is set high at 1 second.

Are there any problems with this strategy? I know you can't access the GUI
in the thread, but haven't seen anything saying I shouldn't start or stop a
timer. Would it perhaps be better to use a volatile boolean flag set true
before the tcf and false after and have the timer check this instead of the
thread running test?

I've given some psuedo code below.

Cheers,
Steph

void CMyDlg::startThread()
{
    m_pThread = AfxBeginThread(MyThreadBegin, (LPVOID)this,
THREAD_PRIORITY_NORMAL);
}

UINT CMyDlg::MyThreadBegin(LPVOID pParam)
{
    CMyDlg* dlgDialog = (CMyDlg *) pParam;
    dlgDialog->MyThread();
    return 0;
}

void CMyDlg::MyThread()
{
    // prepare data - can't use GetPercentComplete here

    // start timer - m_intTimerID is volatile
    m_intTimerID = SetTimer(MINT_TIMERID, 1000, NULL);

    // time consuming function
    m_theDll.TimeConsumingFunction();

    // stop timer
    KillTimer(m_intTimerID);

    // tidy data - can't use GetPercentCompelete here

}

void CMyDlg::OnTimer(UINT nIDEvent)
{
    int intPercent = 0;

    // check it's our timer
    if (m_intTimerID == nIDEvent)
    {
        // if the thread is running
        if (WAIT_TIMEOUT == WaitForSingleObject(m_pThread->m_hThread, 0 ))
        {

            // update progress bar
            blnSuccess = m_theDll.GetPercentComplete(&intPercent);

            // test return value and update progress control
        }
    }
}