Fast Track Visual C++ 6.0 Programming
(Publisher: John Wiley & Sons, Inc.)
Author(s): Steve Holzner
ISBN: 0471312908
Publication Date: 09/01/98

Our program is complete. Run it now, as shown in Figure 9.2, and select the “Find max and min” item in the File menu. This launches the two threads, MaxThread and MinThread.

MaxThread finds the maximum of the array and sets the event that MinThread waits for. MinThread then continues and finds the minimum of the array. The result appears in the view, as shown in Figure 9.2.

Now we’re coordinating multiple threads, which is an important part of true multitasking.

The code for this example, DoubleThreadsView.h and DoubleThreadsView.cpp, appears in Listing 9.2.

// DoubleThreadsView.h : interface of the CDoubleThreadsView class
//
/////////////////////////////////////////////////////////////////////////////

#if !defined(AFX_DOUBLETHREADSVIEW_H__A880E565_A6EB_11D1_887F_D42B07C10710__INCLUDED_)
#define AFX_DOUBLETHREADSVIEW_H__A880E565_A6EB_11D1_887F_D42B07C10710__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

UINT MaxThreadProcedure(LPVOID pParam);
UINT MinThreadProcedure(LPVOID pParam);

struct SData
{
    int array[5];
    int max;
    int min;
    HANDLE flag;
    HWND NotifyWindow;
};

class CDoubleThreadsView : public CView
{
protected: // create from serialization only
    CDoubleThreadsView();
    DECLARE_DYNCREATE(CDoubleThreadsView)

// Attributes
public:
    CDoubleThreadsDoc* GetDocument();
    SData data;
    CWinThread* MaxThread;
    void OnMaxFound(WPARAM wParam, LPARAM lParam);
    CWinThread* MinThread;
    void OnMinFound(WPARAM wParam, LPARAM lParam);

// Operations
public:

// Overrides

    // ClassWizard generated virtual function overrides
    //{{AFX_VIRTUAL(CDoubleThreadsView)
    public:
    virtual void OnDraw(CDC* pDC);  // overridden to draw this view
    virtual BOOL PreCreateWindow(CREATESTRUCT& cs);
    protected:
    virtual BOOL OnPreparePrinting(CPrintInfo* pInfo);
    virtual void OnBeginPrinting(CDC* pDC, CPrintInfo* pInfo);
    virtual void OnEndPrinting(CDC* pDC, CPrintInfo* pInfo);
    //}}AFX_VIRTUAL

// Implementation
public:
    virtual ~CDoubleThreadsView();
#ifdef _DEBUG
    virtual void AssertValid() const;
    virtual void Dump(CDumpContext& dc) const;
#endif

protected:

// Generated message map functions
protected:
    //{{AFX_MSG(CDoubleThreadsView)
    afx_msg void OnFileFindmaxandmin();
    //}}AFX_MSG
    DECLARE_MESSAGE_MAP()
};

#ifndef _DEBUG  // debug version in DoubleThreadsView.cpp
inline CDoubleThreadsDoc* CDoubleThreadsView::GetDocument()
   { return (CDoubleThreadsDoc*)m_pDocument; }
#endif

/////////////////////////////////////////////////////////////////////////////

//{{AFX_INSERT_LOCATION}}
// Microsoft Visual C++ will insert additional declarations immediately
before the previous line.


#endif //!defined(AFX_DOUBLETHREADSVIEW_H__A880E565_A6EB_11D1_887F_D42B07C10710__INCLUDED_)


// DoubleThreadsView.cpp : implementation of the CDoubleThreadsView class
//

#include “stdafx.h”
#include “DoubleThreads.h”

#include “DoubleThreadsDoc.h”
#include “DoubleThreadsView.h”

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif


/////////////////////////////////////////////////////////////////////////////
// CDoubleThreadsView

IMPLEMENT_DYNCREATE(CDoubleThreadsView, CView)

BEGIN_MESSAGE_MAP(CDoubleThreadsView, CView)
    //{{AFX_MSG_MAP(CDoubleThreadsView)
    ON_COMMAND(ID_FILE_FINDMAXANDMIN, OnFileFindmaxandmin)
    ON_MESSAGE(WM_MAX, OnMaxFound)
    ON_MESSAGE(WM_MIN, OnMinFound)
    //}}AFX_MSG_MAP
    // Standard printing commands
    ON_COMMAND(ID_FILE_PRINT, CView::OnFilePrint)
    ON_COMMAND(ID_FILE_PRINT_DIRECT, CView::OnFilePrint)
    ON_COMMAND(ID_FILE_PRINT_PREVIEW, CView::OnFilePrintPreview)
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////////
// CDoubleThreadsView construction/destruction

CDoubleThreadsView::CDoubleThreadsView()
{
    data.flag = CreateEvent(NULL, FALSE, FALSE, NULL);
}

CDoubleThreadsView::~CDoubleThreadsView()
{
}

BOOL CDoubleThreadsView::PreCreateWindow(CREATESTRUCT& cs)
{
    // TODO: Modify the Window class or styles here by modifying
    //  the CREATESTRUCT cs

    return CView::PreCreateWindow(cs);
}

/////////////////////////////////////////////////////////////////////////////
// CDoubleThreadsView drawing

void CDoubleThreadsView::OnDraw(CDC* pDC)
{
    CDoubleThreadsDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);

    pDC->TextOut(0, 0, pDoc->text);
}

/////////////////////////////////////////////////////////////////////////////
// CDoubleThreadsView printing

BOOL CDoubleThreadsView::OnPreparePrinting(CPrintInfo* pInfo)
{
    // default preparation
    return DoPreparePrinting(pInfo);
}

void CDoubleThreadsView::OnBeginPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{
    // TODO: add extra initialization before printing


}

void CDoubleThreadsView::OnEndPrinting(CDC* /*pDC*/, CPrintInfo* /*pInfo*/)
{
    // TODO: add cleanup after printing
}

/////////////////////////////////////////////////////////////////////////////
// CDoubleThreadsView diagnostics

#ifdef _DEBUG
void CDoubleThreadsView::AssertValid() const
{
    CView::AssertValid();
}

void CDoubleThreadsView::Dump(CDumpContext& dc) const
{
    CView::Dump(dc);
}

CDoubleThreadsDoc* CDoubleThreadsView::GetDocument() // non-debug version is inline
{
    ASSERT(m_pDocument->IsKindOf(RUNTIME_CLASS(CDoubleThreadsDoc)));
    return (CDoubleThreadsDoc*)m_pDocument;
}
#endif //_DEBUG

/////////////////////////////////////////////////////////////////////////////
// CDoubleThreadsView message handlers

void CDoubleThreadsView::OnFileFindmaxandmin() 
{
    // TODO: Add your command handler code here
    data.array[0] = 0;
    data.array[1] = 1;
    data.array[2] = 2;
    data.array[3] = 3;
    data.array[4] = 4;

    data.max = 0;

    data.NotifyWindow = m_hWnd;
    MaxThread = AfxBeginThread(MaxThreadProcedure, &data);
    ResetEvent(data.flag);

    MinThread = AfxBeginThread(MinThreadProcedure, &data);

}

UINT MaxThreadProcedure(LPVOID pParam)
{
    SData* pData = (SData*)pParam;

    for(int loop_index = 0; loop_index <= 4; loop_index++){
        if(pData->array[loop_index] > pData->max)
            pData->max = pData->array[loop_index];
    }

    ::PostMessage(pData->NotifyWindow, WM_MAX, 0, 0);

    SetEvent(pData->flag);
    return 0;
}

UINT MinThreadProcedure(LPVOID pParam)
{
    SData* pData = (SData*)pParam;

    WaitForSingleObject(pData->flag, INFINITE);

    pData->min = pData->max;

    for(int loop_index = 0; loop_index <= 4; loop_index++){
        if(pData->array[loop_index] < pData->min)
            pData->min = pData->array[loop_index];
    }

    ::PostMessage(pData->NotifyWindow, WM_MIN, 0, 0);


    return 0;
}

void CDoubleThreadsView::OnMaxFound(WPARAM wParam, LPARAM lParam)
{
    CDoubleThreadsDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);

    char FormattedString[100];
    wsprintf(FormattedString, “Maximum value in array = %d, ”, data.max);
    pDoc->text = FormattedString;

    TerminateThread(MaxThread, 0);

    Invalidate();
}

void CDoubleThreadsView::OnMinFound(WPARAM wParam, LPARAM lParam)
{
    CDoubleThreadsDoc* pDoc = GetDocument();
    ASSERT_VALID(pDoc);

    char FormattedString[100];
    wsprintf(FormattedString, “minimum value in array = %d ”, data.min);
    pDoc->text += FormattedString;

    TerminateThread(MinThread, 0);

    Invalidate();
}

What’s Ahead

In the next chapter, we begin exploring an exceptionally powerful aspect of working with Windows: Dynamic Link Libraries (DLLs). Just about all Windows users have seen DLLs, and in the next chapter, we see how they can be useful to us and how to create them.