Critical section-Updating the Dialog from Workerthread

[Lucress Carol]

Hi every one,
I have a dialog application with a start button, a slider control, an
edit box where the value of the slider control will be displayed and
another edit box where the result of some operations made from a
workerthread will be displayed. When moving the slider, the new value
of the slider should appear in the corresponding edit box and the
workerthread should be aware that the value of the slider has changed
and should update the value of the slider in the calculations being
performed.

I created a class CWorkerThreadMgr (for the thread code) which
contains the followings :
HRESULT Start (HWND hWnd) ; // from where the workerthread will
be started
HWND m_hWnd ; //Window handle to the UI dialog used to post
messages in order to update
//the result of
the calculation in the edit box
HANDLE m_hTread; //handle of the worker thread
static UINT WINAPI ThreadProc( LPVOID lptest );

HRESULT Start (HWND hWnd)
{
HRESULT hr=S_OK;
m_hWnd=hWnd;
m_hThread = (HANDLE)_beginthreadex(NULL,0,ThreadProc,
static_cast<LPVOID>(this), 0,NULL);

return hr;
}

// Implementation in the stdafx.h
#define WM_SENDCALCULATED_VALUE WM_APP + 1

// Implementation in the CStartCalculationDlg.h

CWorkerThreadMgr m_WorkerThreadMgr //instance of the
WorkerThreadMgr
CSliderCtrl m_Slider //member variable of the slider control
CString m_SliderValue // member variable of the edit box, where the
current value of the slider control will be
//displayed

CString m_Calculation // member variable of the edit box where the
calculated result from the workerthread will
//be displayed via PostMessage
afx_msg LRESULT OnSendCalculatedValue( WPARAM, LPARAM );
afx_msg void OnHScroll(UINT nSBCode, UINT nPos, CScrollBar*
pScrollBar);

// Implementation in CStartCalculationDlg.cpp

BEGIN_MESSAGE_MAP(CStartCalculationDlg, CDialog)
…
ON_WM_HSCROLL()
ON_MESSAGE(WM_SENDCALCULATED_VALUE, OnSendcalculatedValue)

void CStartCalculationDlg::OnHScroll(UINT nSBCode, UINT nPos,
CScrollBar* pScrollBar)
{
m_SliderValue.Format(_T("%d"),m_Slider.GetPos());
SetDlgItemText(IDC_SLIDER_VALUE,m_SliderValue);
}

BOOL CStartCalculationDlg::OnInitDialog()
{
m_Slider.SetRange(0,50);
m_Slider.SetTicFreq(5);
SetDlgItemText(IDC_SLIDER_VALUE,_T("0"));
}

void CStartCalculationDlg::OnBnClickedStart()
{
m_WorkerThreadMgr.Start(GetSafeHwnd());
}

static UINT WINAPI ThreadProc( LPVOID lptest )
{
CWorkerThreadMgr* pCalculateMgr = reinterpret_cast< CWorkerThreadMgr*
>( lptest);

//From the thread procedure a random number multiply by the slider
value
//should occur 40 times: rand() *m_SliderValue and the result
displayed in the edit box on the gui

for( UINT uCount = 0; uCount < 40; uCount++ ){

//Check if the slider has been moved
//if so, update the value of the slider for the calculation
...???

//pCalculateMgr-> rand()* m_SliderValue;

PostMessage(pCalculateMgr-> m_hWnd, WM_SENDCALCULATED_VALUE,0,0);
}

}

LRESULT CStartCalculationDlg::OnSendCalculatedValue( WPARAM, LPARAM )
{
// m_SliderValue and m_Slider as critical section ??

m_Calculation.Format(_T("%d"),rand()*m_SliderValue); //???
SetDlgItemText(IDC_CALCULATION, m_Calculation);

return 1;
}

So my questions are the following:
Since I’m not allowed to manipulate the control elements from the
workerthread, how can I implement the “OnSendCalculatedValue”
function?
I have to check by each iteration, if the slider value has been
changed, how can I implement it in the Threadproc or should it be
somewhere else?
How can I implement m_Slider and m_SliderValue as critical section? Or
do I need to create new variables in the CWorkerThreadMgr class?

Thank you

Carol

[scot...@mvps.org]

You're trying to multiply a CString (m_SliderValue) by the rand() result. Change things so the slider value you work with is an int. Then the thread can safely read the int, and it can provide an int result.

When the thread posts the custom message, put the int result into the wParam or lParam that is part of the message. That way the message handler function will receive the new value in the parameter.

[Lucress Carol]

> When the thread posts the custom message, put the int result into the wParam or lParam that is part of the message.  That way the message handler function will receive the new value in the parameter.- Zitierten Text ausblenden -
>
> - Zitierten Text anzeigen -



Thank you for your hint.

>>When the thread posts the custom message, put the int result into the wParam or lParam that is part of the message. That way the message handler function will receive the new value in the parameter.

I declare in the CWorkerThreadMgr class an integer member variable c
and
I post the message to the gui like this:

PostMessage (pCalculateMgr-> m_hWnd,
WM_SENDCALCULATED_VALUE,pCalculateMgr-> c,0);

and the OnSendCalculatedValue looks like this:

LRESULT CStartCalculationDlg::OnSendCalculatedValue( WPARAM, LPARAM )
{

//m_WorkerThreadMgr: instance of the CWorkerThreadMgr class and
declared as member in the
// in the CStartCalculationDlg class

m_WorkerThreadMgr.c=rand()*m_Slider.GetPos();

m_Calculation.Format(_T("%d"),m_WorkerThreadMgr.c);
SetDlgItemText(IDC_CALCULATION, m_Calculation);

return 1;
}

Is it what you meant or did I get it wrong?

thank you

[scot...@mvps.org]

No, that's not what I meant. The posted value is received in the wParam, but you are not doing anything with the received wParam.

LRESULT CStartCalculationDlg::OnSendCalculatedValue( WPARAM newvalue, LPARAM )
{
m_Calculation.Format(_T("%d"), (int) newvalue);

[Lucress Carol]

I'm not quite sure to have understood. So, you mean:

LRESULT CStartCalculationDlg::OnSendCalculatedValue( WPARAM newvalue,
LPARAM )
{

newvalue=rand()*m_Slider.GetPos();

m_Calculation.Format(_T("%d"), (int) newvalue);

...
}

and in the Thread procedure:
PostMessage (pCalculateMgr-> m_hWnd,
WM_SENDCALCULATED_VALUE,pCalculateMgr->(WPARAM)c,0);
right?

Is there a possibility to calculate in the Thread procedure the
operation rand()*m_Slider.GetPos() and send the result via PostMessage
instead of doing it in the OnSendCalculatedValue( WPARAM, LPARAM )
method? In that case, how can I access m_Slider since it's not allowed
to touch gui controls in the Thread procedure?

Thank you

[scot...@mvps.org]

In your original post you said you wanted to compute something in the thread 40 times and display the result in the GUI. So after the thread computes it should post the result in the wParam.

In your most recent post you now have the result (newvalue) shown as a parameter, but you still don't use it! Instead, you are setting newvalue to something else, then displaying the something else. The task of the OnSendCalculatedValue function should be to display the newvalue that it receives from the thread.

>> Is there a possibility to calculate in the Thread procedure the
>> operation rand()*m_Slider.GetPos()

Yes. Whenever the slider changes you get OnHScroll. Have the main thread OnHScroll store the GetPos() in an int variable. The thread can read the int value without synchronization.

[scot...@mvps.org]

In your original post you said you wanted to compute something in the thread 40 times and display the result in the GUI. So after the thread computes it should post the result in the wParam.

In your most recent post you now have the result (newvalue) shown as a parameter, but you still don't use it! Instead, you are setting newvalue to something else, then displaying the something else. The task of the OnSendCalculatedValue function should be to display the newvalue that it receives from the thread.

>> Is there a possibility to calculate in the Thread procedure the
>> operation rand()*m_Slider.GetPos()

Yes. Whenever the slider changes you get OnHScroll. Have the main thread OnHScroll store the GetPos() value in an int variable. The thread can read the int value without synchronization.

[Lucress Carol]

How can the thread read that int value? should the gui post a
PostThreadMessage to the thread with the value??

[Mikel]

How about something like this:

class CWorkerThreadMgr
{
// Your stuff

protected:
int m_pos;

public:
void SetPos(int pos) { m_pos = pos; }
int GetPos() { return m_pos; }

}

void CStartCalculationDlg::OnHScroll(UINT nSBCode, UINT nPos,
CScrollBar* pScrollBar)
{

// Whatever you have now

m_WorkerThreadMgr.SetPos(m_Slider.GetPos());

}

static UINT WINAPI ThreadProc( LPVOID lptest )
{
CWorkerThreadMgr* pCalculateMgr = reinterpret_cast<
CWorkerThreadMgr*>( lptest);

for( UINT uCount = 0; uCount < 40; uCount++ ){

int value = pCalculateMgr->rand() *pCalculateMgr.GetPos();
PostMessage(pCalculateMgr-> m_hWnd, WM_SENDCALCULATED_VALUE,
value, 0);
}
}

LRESULT CStartCalculationDlg::OnSendCalculatedValue( WPARAM v,
LPARAM )
{
m_Calculation.Format(_T("%d"), (int)v);
SetDlgItemText(IDC_CALCULATION, m_Calculation);

return 1;
}

[Lucress Carol]

> }- Zitierten Text ausblenden -
>
> - Zitierten Text anzeigen -

Thank you for the hint. I'm going to try it out ...