C / C++ / MFC

Terminating Threads! [modified]

16-Sep-10 10:39

overloaded Name wrote:
how do I get the names of the available devices in a TAPI app??

Wouldn't that be up to the app to provide you with that information? Confused | :confused:

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Caslen16-Sep-10 3:21

16-Sep-10 3:21

I have an MFC MDI app in which I have included a docking control bar (Cristi Posea - CSizingControlBar - a resizable control bar) The controlbar has a dialog associated with it which, amongst other things, continuously grabs data from a PCI A/D card using a worker thread.

I have the following code,
first initialise the control bar and associated dialog:-

in MainFrm.h:-

class CMainFrame : public CMDIFrameWnd
{
	DECLARE_DYNAMIC(CMainFrame)
public:
	CMainFrame();

	CMainControlBar	m_MCB;			//the control bar
	CDataControls	m_GrabDataDialog; 	//the dialog attached to the control bar

//other stuff...
.
.
.
}

then in MainFrm.cpp:-

int CMainFrame::EnableControlBar()
{

	if (!m_MCB.Create(_T("Data Window"), this, 50))
	{
		TRACE0("Failed to create Data Window\n");
		return -1;
	}
	m_MCB.SetBarStyle(m_MCB.GetBarStyle() | CBRS_TOOLTIPS | CBRS_FLYBY | CBRS_SIZE_DYNAMIC );
	m_MCB.EnableDocking(CBRS_ALIGN_ANY);

#ifdef _SCB_REPLACE_MINIFRAME
    m_pFloatingFrameClass = RUNTIME_CLASS(CSCBMiniDockFrameWnd);
#endif 

	DockControlBar(&m_MCB, AFX_IDW_DOCKBAR_LEFT);
	
	//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	//~~~~  Attach Controls Dialog  
	//~~~~  to  Window if possible
	//~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
	if (!m_DataDialog.Create(IDD_MAINCONTROLS,&m_MCB))
	{
		TRACE0("Failed to create instant bar child\n");
		return -1;		// fail to create
	}

	//show the bar!
	m_DataDialog.ShowWindow(SW_SHOW);

	return 0;
}

Next, set up the thread:-

class CDataControls : public CDialog
{
// Construction
public:
	virtual ~CDataControls();
	CDataControls(CWnd* pParent = NULL);   

	CGraphDraw m_Graph; //the custom control
	void DoDataDraw(); //passes data to the custom control
	void DoDataGrab(); //grabs data from an A/D converter

	BOOL m_TerminateThreads; 	//flag to terminate the thread
	CWinThread *pDataGrabThread; 	//thread pointer

	double	Sig[1024];

//other stuff...
.
.
.
};

and:-

BOOL CDataControls::OnInitDialog() 
{
	CDialog::OnInitDialog();
	
	//Initialise Custom Control
	m_Graph.Initialise();

	//Setup Grab Thread
	pDataGrabThread = AfxBeginThread(DataGrabThread,this,THREAD_PRIORITY_NORMAL, 0, CREATE_SUSPENDED);		
        if(pDataGrabThread==NULL)
		AfxMessageBox(L"Crap Thread");

	pDataGrabThread->m_bAutoDelete=FALSE;
	pDataGrabThread->ResumeThread();
	
	
	return TRUE;
}

Now the actual thread:-

UINT DataGrabThread(LPVOID me)
{
	CDataControls *self = (CDataControls *)me;

	while(self->m_TerminateThreads!=0)
	{
		self->DoDataGrab(); 	//go and grab the data
		Sleep(100);		//don't hog the CPU
	}
	return 0;
}

To close the thread when the controlbar closes I have:-

void CDataControls::OnClose() 
{
	m_TerminateThreads=FALSE;  	//Signal terminate the thread

	WaitForSingleObject(pDataGrabThread->m_hThread,10000); //give it chance to stop
	delete pDataGrabThread; 	//then delete it
	
	CDialog::OnClose();
}

Now I assumed that when I close the main application that it would take care of closing the controlbar sensibly via CDataControls::OnClose() but it doesn't - CDataControls::OnClose() isn't called at all, and I get 'MFC Application has encountered a problem...' error.

So now I have the following in the MainFrm.cpp:-

void CMainFrame::OnClose() 
{
	::SendMessage(m_ControlsDialog,WM_CLOSE,0,0);  //send a message to close the dialog and thread
	
	CMDIFrameWnd::OnClose();
}

This now works perfectly! No errors, no memory leaks just apparently a nice clean finish. My question then, is this the correct way to go about this? I haven't had much experience with threads and although this seems to work well and I'm fairly happy with it I would like to know if it is the right way to do it and if not how else might I go about closing a thread running in a non-modal dialog when the main application is closed?

modified on Thursday, September 16, 2010 11:02 AM

Cool_Dev16-Sep-10 5:26

Cool_Dev

16-Sep-10 5:26

i think its not a safe practice to access the m_TerminateThread variable in main UI thread from another thread, without using any locking mechanisms. Better to use an Event object, which is initially non-signalled, set it to signaled in CDataControls::OnClose(), and wait on thread handle. And in Thread function,

//m_hEvent is the Event handle in CDataControls
while(WAIT_OBJECT_0 != WaitForSingleObject(self->m_hEvent,0))
{
	self->DoDataGrab(); 	//go and grab the data
	Sleep(100);		//don't hog the CPU
}

or,

while(WAIT_OBJECT_0 != WaitForSingleObjectself->m_hEvent,100))
{
	self->DoDataGrab(); 	//go and grab the data
}

Roger Allen16-Sep-10 5:50

Roger Allen

16-Sep-10 5:50

Actually it is safe in this particular case. As the worker thread only ever reads the state of the variable, but he has to make sure it is reading the changes on each loop, i.e. it must be declared [code]mutable[/code] elase a compiler optimisation step may remove the follow on reads.

As long as multiple threads are not read/writing it should be fine.

If you vote me down, my score will only get lower

Luc Pattyn16-Sep-10 6:14

Luc Pattyn

16-Sep-10 6:14

IMO it needs to be no wider than what can be handled atomically (hence 32-bit) AND declared volatile. Then it does not matter how many readers there are, as long as there is only one writer all is fine. With several writers, it most often needs a lock of some kind.

Smile | :)

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Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.

Caslen16-Sep-10 5:59

16-Sep-10 5:59

Cool_Dev wrote:
Better to use an Event object,

Thanks, I tried this - it works ok but I still need the WaitForSingleObject() in the CDataControls::OnClose() (see below) Why is this?

void CDataControls::OnClose() 
{	
	SetEvent(g_Event);	
	WaitForSingleObject(pDataGrabThread>m_hThread,1000); //give it chance to stop	delete pDataGrabThread; 	//then delete it	

	CDialog::OnClose();
}

image processing toolkits | batch image processing

C^hris L^osinger16-Sep-10 6:02

C^hris L^osinger

16-Sep-10 6:02

because you need to give the thread a chance to see the event and react to it.

Caslen16-Sep-10 6:08

16-Sep-10 6:08

Thanks! Sometimes it's good to know why, not just that it works Smile | :)

David Crow16-Sep-10 5:53

16-Sep-10 5:53

Caslen wrote:
::SendMessage(m_ControlsDialog,WM_CLOSE,0,0); //send a message to close the dialog and thread

You've not shown how m_ControlsDialog was declared. I assume it's safe to send a message to. If it's a modeless dialog, why not just call DestroyWindow()?

Caslen wrote:
while(self->m_TerminateThreads!=0)

This loop is suspect if m_TerminateThreads is not declared as volatile. Otherwise, it may or may not execute, or it may fail to end. Because m_TerminateThreads is not being changed within the loop, the compiler would likely optimize it out.

A better way of having the secondary thread end is to have the primary thread signal an event.

Caslen16-Sep-10 6:04

16-Sep-10 6:04

I already figured out the 'volatile' thing - I was more concerned about why I had to 'SendMessage' from CMainFrame::OnClose() - why wasn't CDataControls::OnClose() automatically closed when the App is closed?

David Crow16-Sep-10 6:45

16-Sep-10 6:45

Caslen wrote:
...why wasn't CDataControls::OnClose() automatically closed when the App is closed?

Because it was in the secondary thread, which was not terminating, perhaps? To test this, change your code to:

WaitForSingleObject(pDataGrabThread->m_hThread, INFINITE);

Caslen16-Sep-10 22:31

16-Sep-10 22:31

Ok, that is probably it - but it's correct to use SendMessage() from CMainframe to close it though?

David Crow17-Sep-10 2:56

17-Sep-10 2:56

Caslen wrote:
...but it's correct to use SendMessage() from CMainframe to close it though?

Is the dialog modeless?

Caslen17-Sep-10 3:04

17-Sep-10 3:04

Yes it is.

David Crow17-Sep-10 3:09

17-Sep-10 3:09

Then just call DestroyWindow().

Roger Allen16-Sep-10 5:54

Roger Allen

16-Sep-10 5:54

Note that you should declare m_TerminateThreads as ~~mutable~~ volatile as a compiler optimisation could break your code.
These lines

while(self->m_TerminateThreads!=0)
{
self->DoDataGrab(); 	//go and grab the data

could be interpreted as the compiler as:

if (self->m_TerminateThreads!=0)
{
for (;;)
{
self->DoDataGrab();

If you vote me down, my score will only get lower

Line Drawing

Benjamin Bruno16-Sep-10 1:17

Benjamin Bruno

16-Sep-10 1:17

Hi I want to draw line on OnMouseMove function of a dialog class.I want to draw
the line in one color(fixed color not inverse color ),but it is showing in
different/inverse color. If I omit SetROP2 the line will get spread.

<code>
CDC* pDC = this->GetDC();
int nR2 = pDC->SetROP2( R2_NOTXORPEN );

pDC->MoveTo(m_StartPoint);
pDC->LineTo(m_Previouspoint);

m_Previouspoint = point;
pDC->MoveTo(m_StartPoint);
pDC->LineTo(point);

</code>
How to solve it? Sniff | :^)

thanks

Re: Line Drawing

Shivanand Gupta16-Sep-10 1:28

Shivanand Gupta

16-Sep-10 1:28

Please find previous thread.
that will help you

Re: Line Drawing

David Crow16-Sep-10 5:45