Re: Starting a timer from a worker thread

=?Utf-8?B?U3RlcGg=?= <steph@newsgroups.nospam>
Mon, 14 May 2007 06:34:01 -0700
Thanks Joe, I shall take a look at Multimedia timers.

However, I have actually implemented this in my code and the timer does
fire, despite not having a message pump. I was originally asking in case I
could not rely on this behaviour, but now I am confused as to why it works at
all. Any ideas?

BTW what are your thoughts on using a boolean flag around the time consuming
function? Is that a bad idea?

Best regards,

"Joseph M. Newcomer" wrote:

You can use a multimedia timer (which executes in yet another thread). You cannot use
SetTimer or a timer callback because these require a message pump in the thread, and you
have a worker thread. You can *call* SetTimer, but nothing at all will *happen* because
there is no message pump to dispatch the callback.

On Mon, 14 May 2007 05:48:01 -0700, Steph <steph@newsgroups.nospam> wrote:


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.


void CMyDlg::startThread()
   m_pThread = AfxBeginThread(MyThreadBegin, (LPVOID)this,

UINT CMyDlg::MyThreadBegin(LPVOID pParam)
   CMyDlg* dlgDialog = (CMyDlg *) pParam;
   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

   // stop timer

   // 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

Joseph M. Newcomer [MVP]
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