A thread, a custom object...
Michel Robert -- michero@login.net
Friday, May 03, 1996
Win95, VC4.0, MFC
Problem: a custom object of mine (non mfc) has a function that does a very
long computation and writes to disk. I placed this call in a thread (using
globals mostly). If the user closes the window, the main thread uses another
of the object's function to set a member flag which the long computation
polls on each iteration. About 1 time out of 3, the program hangs and I must
give it the 3 finger salute. I don't have a clue why this is happening.
There are no AfxMessageBox calls. Suggestions will be appreciated. Some
code follows:
void CMainFrame::OnClose()
{
/* if the object's long computation function is in progress */
if(bInProgress)
{
//sets a member flag which is polled during long computations
mpeObject.AbortBuild();
}
/* even if not bInProgress, the thread could still be running */
if(pthread)
{
g_eventKill.SetEvent();
/* wait for the thread to acquiesce */
while(!bCancel);
}
CFrameWnd::OnClose();
}
UINT MyThread(LPVOID pParam)
{
HWND hw = (HWND)pParam;
CStatic* wndStatic;
wndStatic = (CStatic*)CWnd::FromHandle(hw);
wndStatic->SetWindowText("banzaiiiiiiiiiiii");
// the object's function will also grab the static and use it to blabber
wndStatic->Detach();
MPermutation::Error mpeError;
NTYPE j;
for(j = 9; j < 10; j++)
{
bInProgress = TRUE;
mpeError = mpeObject.OpenSet("h:\\temp\\",j,hw,FALSE);
bInProgress = FALSE;
if(mpeError) /* object has polled the abort member flag and exited
{
// ALWAYS - this is the path I'm having trouble with
break;
}
// a loop starts here, but this is of no concern (for now...)
if(::WaitForSingleObject(g_eventKill.m_hObject,0) == WAIT_OBJECT_0)
break;
else
{
// some more processing
}
pthread = NULL;
bCancel = TRUE; // inform this thread is done
return TRUE;
}
TIA
Michel Robert
Montreal
Marty Fried -- mfried@linex.com
Saturday, May 04, 1996
[Mini-digest: 4 responses]
At 03:07 AM 5/3/96 -0400, Michel Robert wrote:
>Win95, VC4.0, MFC
>
>Problem: a custom object of mine (non mfc) has a function that does a very
>long computation and writes to disk. I placed this call in a thread (using
>globals mostly). If the user closes the window, the main thread uses another
>of the object's function to set a member flag which the long computation
>polls on each iteration. About 1 time out of 3, the program hangs and I must
>give it the 3 finger salute. I don't have a clue why this is happening.
>There are no AfxMessageBox calls. Suggestions will be appreciated. Some
>code follows:
> . . .
> /* even if not bInProgress, the thread could still be running */
> if(pthread)
> {
> g_eventKill.SetEvent();
> /* wait for the thread to acquiesce */
> while(!bCancel);
> }
> CFrameWnd::OnClose();
I haven't tried to fully analyze your code, but one thing I notice is the line
"while(!bCancel)". This is eating up unnecessary cpu time that is better used
by the thread to finish what it's doing. Better to use WaitForSingleObject with
the thread handle as the object to wait for. Also, if the thread needs any
message processing, you aren't doing it while waiting, so if this is the case,
you may need to have a fairly short timeout in the wait, and process messages
in between waits.
Hope this makes sense.
________________________________
Marty Fried (mfried@linex.com)
Marin County, California
-----From: mikeblas@interserv.com
On Fri, 3 May 1996, michero@login.net (Michel Robert) wrote:
>Win95, VC4.0, MFC
Thanks.
> if(pthread)
> {
> g_eventKill.SetEvent();
> /* wait for the thread to acquiesce */
> while(!bCancel);
> }
This is a very poor way to check for the termination of the thread. It is
poor because it sits and polls, sucking CPU time that the other thread could
be using--you could avoid that problem by using
while (!bCancel)
sleep(100);
But what you _really_ should do is use the mulitthreading features the
operating system gives you: wait for the handle of the thread. The thread
handle is unsignalled while the thread is running, and signalled when the
thread has finished.
.B ekiM
--
TCHAR szDisc[] = _T("These words are my own; I do not speak for Microsoft.");
-----From: Frank McGeough
Michel Robert wrote:
>
> Win95, VC4.0, MFC
>
> Problem: a custom object of mine (non mfc) has a function that does a very
> long computation and writes to disk. I placed this call in a thread (using
> globals mostly). If the user closes the window, the main thread uses another
> of the object's function to set a member flag which the long computation
> polls on each iteration. About 1 time out of 3, the program hangs and I must
> give it the 3 finger salute. I don't have a clue why this is happening.
> There are no AfxMessageBox calls. Suggestions will be appreciated. Some
> code follows:
>
I have a similar program that is running a pool of worker threads. The worker
threads are created by a Workbench object that is created by the Document
class. The threads are derived from CWinThread. The Workbench object keeps
the CWinThread objects and it sets a flag in the worker threads to indicate
that they should exit. The Workbench exposes a method that allows a caller to
see if the threads are running and to request them to exit. The Workbench
object checks to see if they have exited by :
VERIFY(::GetExitCodeThread(pWorkerThread->m_hThread, &dwStatus));
if (dwStatus == STILL_ACTIVE)
// we haven't exited yet
When the user chooses to close the app, I call the Workbench and ask it to
stop the threads, hide the app right away and then wait for the threads
to respond to the flag that I set (I return FALSE to the request to
close the frame & post another WM_CLOSE msg while my threads are still
running). This seems to work fine for this particular app. I haven't had
any problems with it hanging. I guess I would not have your MainFrame use
the same variable that you're using to signal the threads to stop. I would
suggest using the thread information itself and checking the exit code.
__________________________________________________
Frank McGeough fm@synchrologic.com
Synchrologic, Inc. (http://www.synchrologic.com/)
Voice: 404.876.3209 Fax: 404.876.3809
-----From: Niels Ull Jacobsen
At 03:07 03-05-96 -0400, you wrote:
>Win95, VC4.0, MFC
>
>Problem: a custom object of mine (non mfc) has a function that does a very=
=20
>long computation and writes to disk.=20
Just a note: If you're concerned about speed and the disk writes happens=
during=20
the computation (and not just at the end), you should probably put the
computation
and the writing to disk in separate threads. That way the CPU won't be kept
waiting for=20
the disk.=20
>I placed this call in a thread (using=20
>globals mostly). If the user closes the window, the main thread uses=
another=20
>of the object's function to set a member flag which the long computation=20
>polls on each iteration. About 1 time out of 3, the program hangs and I=
must=20
>give it the 3 finger salute. I don't have a clue why this is happening. =
=20
>There are no AfxMessageBox calls. Suggestions will be appreciated.
> Some code follows:
Why are you using both an abort flag and a Kill event. Wouldn't=20
a Kill event suffice? Just SetEvent() in mpeAbortBuild().=20
>
>void CMainFrame::OnClose()=20
>{
> /* if the object's long computation function is in progress */
> if(bInProgress)=20
> {
> //sets a member flag which is polled during long=
computations
> mpeObject.AbortBuild();=20
> }
> /* even if not bInProgress, the thread could still be running */
> if(pthread)
> {
> g_eventKill.SetEvent();
> /* wait for the thread to acquiesce */
> while(!bCancel);
I think your problem is here. This is busy waiting - always a bad idea.=20
If your worker thread has lower priority than the main thread, couldn't=20
this prevent it from running at all? Or, if the compiler is smart,=20
perhaps it puts bCancel in a register? Is bCancel declared volatile?=20
I'd use a WaitForSingleObject on the thread's handle with some reasonable
time-out.
> }
> CFrameWnd::OnClose();
>}
>
>
>
>UINT MyThread(LPVOID pParam)
>{
>HWND hw =3D (HWND)pParam;
>CStatic* wndStatic;
>wndStatic =3D (CStatic*)CWnd::FromHandle(hw);
>wndStatic->SetWindowText("banzaiiiiiiiiiiii");
> // the object's function will also grab the static and use it to blabber
>wndStatic->Detach();
>MPermutation::Error mpeError;
>NTYPE j;
>for(j =3D 9; j < 10; j++)
> {
> bInProgress =3D TRUE;
> mpeError =3D mpeObject.OpenSet("h:\\temp\\",j,hw,FALSE);
> bInProgress =3D FALSE;
> if(mpeError) /* object has polled the abort member flag and exited
> {
> // ALWAYS - this is the path I'm having trouble with
> break;
> }
> // a loop starts here, but this is of no concern (for now...)
> if(::WaitForSingleObject(g_eventKill.m_hObject,0) =3D=3D=
WAIT_OBJECT_0)
> break; =20
> else
> {
> // some more processing
> }
>pthread =3D NULL;
>bCancel =3D TRUE; // inform this thread is done
>return TRUE;
>}
>
>
>
>TIA
>Michel Robert
>Montreal
>
>
>
>
>
>
Niels Ull Jacobsen, Kr=FCger A/S (nuj@kruger.dk)
Everything stated herein is THE OFFICIAL POLICY of the entire Kruger group
and should be taken as legally binding in every respect. Pigs will grow
wings and fly.
David Shoots -- dshoots@lmcorp.com
Thursday, May 09, 1996
mfc-l@netcom.com,Internet writes:
>Problem: a custom object of mine (non mfc) has a function that does a very
>long computation and writes to disk. I placed this call in a thread (using
>globals mostly). If the user closes the window, the main thread uses
another
>of the object's function to set a member flag which the long computation
>polls on each iteration. About 1 time out of 3, the program hangs and I must
>give it the 3 finger salute. I don't have a clue why this is happening.
>There are no AfxMessageBox calls. Suggestions will be appreciated. Some
>code follows:
Are you using SendMessage() from your worker thread to convey information to
your main thread? This can cause the deadlock requiring an EndTask. (If
your main thread has signalled and is waiting for the thread to die, and the
thread calls SendMessage(), the worker thread will hang)
DWS
"I don't know for whom I'm speaking..."
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