Background Task Dialog

Sample screenshot

Introduction

Hi, my name is Mauro H. Leggieri, a Windows and Game programmer. I made a little thing that may be useful, and want to share with you.

I wrote a class named CBackgroundTaskDialog derived from the standard CDialog class. It is a wrapper for dialog boxes where you must do a long-time process, optionally showing the progress information, but you don't want your application to appear to be hung.

Using the code

The code simply creates a background thread and calls some member functions where you write your own code and have some members to control when to start/stop the background process.

To use the code in your project, first add the BackgroundTaskDialog.cpp and BackgroundTaskDialog.h files to your project.

Then, in the header file of the dialog you want to subclass, add the include "BackgroundTaskDialog.h" statement and replace all CDialog words with CBackgroundTaskDialog and add the following member declarations to the class:

class your_dialog_class : public CBackgroundTaskDialog
{
  // Class definition an so on...
  // Code that you must add to the class:

public:
  void RunBackgroundTask();
}

After this, replace in the CPP file of the dialog all CDialog words with CBackgroundTaskDialog too and add the following members code:

void your_dialog_class_name::RunBackgroundTask()
{
  //Here you should add the code for the long-term process to do
  
  //At regular intervals you should call then 
  //CheckForBackgroundTaskAbort function
  //to check for an abort signal. If the function 
  //returns TRUE, usually simply return
}

To start the background process, you must use the StartBackgroundTask function. It returns a value of 1 if all is ok or less than 0 if an error occurs. The function is usually used in the OnInitDialog function.

BOOL your_dialog_class_name::OnInitDialog()
{
  // Code added by MFC AppWizard and your own code

  // Example code to add:

  if (StartBackgroundTask() < 0)
  {
     AfxMessageBox(_T("Error"));
     PostMessage(WM_CLOSE, 0, 0);
     return TRUE;
  }

  return TRUE;
}

At last, if you want to abort the background process, call the StopBackgroundTask function.

See the example project because it has more explanations.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Mauro Leggieri

Web Developer

Argentina

Member

My name is Mauro Leggieri. I am 30 year-old, married and have a child.

I am a system engineer (UTN university) and am being programming for more than 20 years from the C64 to the PC and some microcontrollers.

Mostly of my time, I program games for Windows.

Soon, my site http://www.mauroleggieri.com.ar

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Can we achieve this without a "Dialog" [modified]

IScribe

15:25 3 Jun '07

Hello Mauro Leggieri,

Thanks for your effort. I am a newbie and this is definitely something I could use as I would like to do some background processing in my Windows Application (CWinApp)! However, can we start/stop these background tasks without a Dialog? If so, could you guide me accordingly. Thanks in advance and appreciate your response/support.

Best Wishes,
IScribe

-- modified at 21:44 Sunday 3rd June, 2007

Some remarks

cristitomi

5:54 22 Mar '07

Hi!
In functions OnBtnStartStop() and RunBackgroundTask() from the demo dialog class, try and avoid the CWnd* wnd pointer. It's useless and it's more prone to errors. The functions simply could look like this:

void CBackgroundTaskDialogDemoDlg::OnBtnStartStop() 
{
    // Check if the background process is running
    if (IsBackgroundTaskRunning() == FALSE) 
    {
	// Start background process
	if (StartBackgroundTask() < 0) 
	{
	    GetDlgItem(IDC_STC_PROGRESS)->SetWindowText(
		_T("Error: Cannot start background thread."));
	    return;
	}
 
	GetDlgItem(IDC_BTN_STARTSTOP)->SetWindowText("Stop");
    }
    else 
    {
	// Abort background process
	StopBackgroundTask();
	GetDlgItem(IDC_STC_PROGRESS)->SetWindowText(_T("Thread was 
              stopped."));
	GetDlgItem(IDC_BTN_STARTSTOP)->SetWindowText("Start");
    }
 
    return;
}

and

void CBackgroundTaskDialogDemoDlg::RunBackgroundTask()
{
    TCHAR buf[1024];
    int i;
    for (i = 0; i < 500; i++) 
    {
	// Check if I have to abort
	if (CheckForBackgroundTaskAbort() != FALSE)
	    return;
	// Update status text
	_stprintf(buf, _T("Counting %ld of 500"), i+1);
	GetDlgItem(IDC_STC_PROGRESS)->SetWindowText(buf);
	// Mini delay
	Sleep(10);
    }
    // Update status text
    GetDlgItem(IDC_STC_PROGRESS)->SetWindowText(_T("Thread has finished 
          successfully."));    	
    GetDlgItem(IDC_BTN_STARTSTOP)->SetWindowText("Start");
 
    return;
}

The code is also more readable.
Greatings,
Christian.

I am in love with VC++

Re: Some remarks

Mauro Leggieri

9:51 22 Mar '07

Hi,

I usually use the CWnd pointer when I have to call many functions in the object.

If I have to do:



GetDlgItem(IDC_STC_PROGRESS)->SetWindowText(...

GetDlgItem(IDC_STC_PROGRESS)->SendMessage(...

GetDlgItem(IDC_STC_PROGRESS)->MoveWindow(...

I prefer to do



CWnd *lpWnd;

 

lpWnd = GetDlgItem(IDC_STC_PROGRESS);

lpWnd->SetWindowText(...

lpWnd->SendMessage(...

lpWnd->MoveWindow(...

It is faster because it works like a cache avoiding asking the s.o. for the handle of the child control each time I want to access it.

Also remember that it is a demo code. Always improvements can be done.

Best regards,
Mauro.

Re: Some remarks

cristitomi

12:38 22 Mar '07

Ok! I get the point. Thanks. Best wishes, Christian. I am in love with VC++
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Re: Some remarks

Mauro Leggieri

3:35 23 Mar '07

Good luck! Mauro.
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Re: Some remarks

Member 3691

0:34 15 Mar '09

Thank you for your improved codes.

- OnBtnStartStop();
- RunBackgroundTask();

// some modified and attached to use again later.
// 1. Removed: sleep();
// 2. Added: _T() to some omitted non-unicode string. (although it is unnecessary)
// 3. Changed: "GetDlgItem()->SetWindowText()" => SetDlgItemText()

void CBackgroundTaskDialogDemoDlg::OnBtnStartStop() 
{    
    // Check if the background process is running    
    if (IsBackgroundTaskRunning() == FALSE)     
    {	
        // Start background process	
        if (StartBackgroundTask() < 0) 	
        {	    
            SetDlgItemText(IDC_STC_PROGRESS, _T("Error: Cannot start background thread."));
            return;	
        }
        SetDlgItemText(IDC_BTN_STARTSTOP, _T("Stop"));
    }    
    else
    {	
	// Abort background process	
	StopBackgroundTask();	
	SetDlgItemText(IDC_STC_PROGRESS, _T("Thread was stopped."));
	SetDlgItemText(IDC_BTN_STARTSTOP, _T("Start"));
    }
    return;
}
 
void CBackgroundTaskDialogDemoDlg::RunBackgroundTask()
{
    TCHAR buf[1024]={0,};
    int i=0;
 
    for (i=0; i < 500; i++)     
    {	
        // Check if I have to abort	
        if (CheckForBackgroundTaskAbort() != FALSE)	    
            return;
        
        // Update status text	
        _stprintf(buf, _T("Counting %ld of 500"), i+1);
        SetDlgItemText(IDC_STC_PROGRESS, buf);	
    }
    
    //Update status text
    SetDlgItemText(IDC_STC_PROGRESS, _T("Thread has finished successfully."));
    SetDlgItemText(IDC_BTN_STARTSTOP, _T("Start"));
    return;
}

Taeha Kim

Re: Some remarks

Mauro Leggieri

10:23 15 Mar '09

Thanks Kim. The Sleep API is called in order to give a chance to the main thread to update the static control text. Sleep(1) should be enough. Best regards, Mauro H. Leggieri
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Re: Some remarks [modified]

Member 3691

15:25 15 Mar '09

Thank you for saying that and your article. The article is very useful, I think. By the way if the function (+pWnd) is inserted, cause access violation (0xC0000005). The case is effected in simple robustness test, not in reliability one. But this is irrelevant to your article and it's main objective. It's only private tendency. Cheers. Taeha Kim modified on Sunday, March 15, 2009 9:31 PM
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Re: Some remarks

Mauro Leggieri

7:15 16 Mar '09

I don't understand what do you mean with "funcion (+pWnd) is inserted". If I could help tell me
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what to do when using multiple base class?

_kane_

8:21 27 Dec '05

hi,

I have used your class in a lot of programs without a problem. However, now there is an issue because in this program the base class is not CDialog. You see, i am using Massimo Collurcio's UI class http://www.codeproject.com/miscctrl/hmxcontrols.asp[here^] and so my default constructors etc are different and causing errors. Is there a workaround for this?

thanks Smile | :)

"Some guys hack just to get themselves a girlfriend.What a pathetic reason huh ?"

Re: what to do when using multiple base class?

Mauro Leggieri

8:50 27 Dec '05

Hi Kane,

I'm writing a fast answer because I'm at work. Please, let me know if you need further assistance.

You should add to BackgroundTaskDialog.cpp and .h the three dialog constructors...

CBackgroundTaskDialog(UINT uResourceID, CWnd* pParent = NULL);
CBackgroundTaskDialog(LPCTSTR pszResourceID, CWnd* pParent = NULL);
CBackgroundTaskDialog();

... and their implementations. The first one is already defined and implemented so you must add the second and the third.

In the implementation remember to call the corresponding CDialog base member function and put

hKillBackgroundThreadEvent = hDoneBackgroundThreadEvent = NULL;
lpBackgroundThread = NULL;

inside each constructor in order to initialize the variables.

Then you can change the HMXDialog.h file to make CHMXDialog a derived class of CBackgroundTaskDialog and the HMXDialog.cpp to call CBackgroundTaskDialog constructors instead of CDialog ones.

Best regards,
Mauro H. Leggieri

Re: what to do when using multiple base class?

_kane_

7:04 29 Dec '05

thanks with your help i managed to do it "Some guys hack just to get themselves a girlfriend.What a pathetic reason huh ?"
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Re: what to do when using multiple base class?

Mauro Leggieri

8:49 29 Dec '05

Perfect. Happy new year! Mauro.
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RC -4 after 85 DoModal()s

Anonymous

3:40 29 Jun '05

Hello, alfter calling the StartBackgroundTask in the Initdialog functions it returns -4! Some known Problems? regards alex
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Re: RC -4 after 85 DoModal()s

MX-Mauro

12:36 29 Jun '05

Hi Alex,

As you see in the code, return value -4 implies that AfxBeginThread failed. I think ( really i'm guessing Smile | :)

) that the problem can be a memory, resource and/or gdi object leak in the code that is consuming system resources and then Windows cannot create the new thread.

Also, if you are using the StopBackgroundTask with a timeout, check if the function is really waiting the thread to finish or the function is terminating it.

Tell me if you have any news.

Best regards,
Mauro H. Leggieri

Any new version?

Anonymous

14:23 23 Mar '05

the program crashed! Any new version?
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Re: Any new version?

MX-Mauro

13:00 29 Jun '05

Hi, Sorry for the very late answer. I haven't made modifications to the code. Tell me more about the program crash so I can help you. Best regards, Mauro H. Leggieri.
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Re: Any new version?

dennisV

21:56 17 Aug '05

I'm not the original poster of that question, but the crash that happens after starting/stopping a few times is still there it seems, so if you've fixed it, could you please post the code that needs to be changed? Thanks. // MCP, MCSD // Software for animal shelters // http://www.smartpethealth.com
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Re: Any new version?

MX-Mauro

1:29 18 Aug '05

Hi Dennis, The version at codeproject is the latest and I make the test of starting and stopping the background task and seeing if there is any leak and nothing happens. Please send me more details about the crash message and if it occurs in the demo app I uploaded. I want to resolve the problem if there is one. Best regards, Mauro H. Leggieri
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Re: Any new version?

Anonymous

3:43 18 Aug '05

Hi, It's not a leak actually, it's a crash. I don't have the call stack at the moment (different computer), but if you do start-stop a few times quickly (15-20 times?), then it's going to come down crashing. If you can't reproduce it, I'll try to get you a call stack and the offending variable sometime soon.
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Re: Any new version?

dennisV

3:45 18 Aug '05

That was me, not logged in // MCP, MCSD // Software for animal shelters // http://www.smartpethealth.com
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Re: Any new version?

MX-Mauro

7:40 18 Aug '05

Hi Dennis, I made a very quick start/stop sequence as you (also using the spacebar to hit the button faster than mouse clicks) and nothing happens. I have a Pentium 4 1.8Ghz with 256mb ram. Send me the stack trace when you can to check. Greetings, Mauro.
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Backgound process

Emmanouel

1:29 22 Jun '04

Hello,

I am trying to set up a windows .net application form that apart from everything else would run a background process for downloading a web page and set it up as a backgound wallpaper.

I am trying to use the code in the backgound task dialog, i've managed to define Runbackgroundtask with the code i would like to use but when i try to use the startbackgoundtask in the initialiseComponent in order to run the backgound process, i get a compile error of

C2352: 'CBackgroundTaskDialog::StartBackgroundTask' : illegal call of non-static member function

Any sugestions ?

Thanks

Re: Backgound process

MX-Mauro

4:15 22 Jun '04

Hi,

According to MSDN the problem arises when you call a nonstatic member from a static one or when you directly use the 'CBackgroundTaskDialog::StartBackgroundTask()' sentence to try to start the background task.

The CBackgroundTaskDialog is used as a base class of the dialog and you must call the StartBackgroundTask function using, for e.g., this->StartBackgroundTask();

If you can send me the piece of code that generates the problem I shall have a better view of the problem.

Best regards, Mauro H. Leggieri.

Single-threaded application

maciejr

21:19 9 May '04

Hi,

I am trying to use your class for my program, but with a single-threaded program design it is not straightforward.

The effect I wanted is: during a lengthy operation (such as reading a large data file referenced in a document being loaded) a "Patience" dialog box with a simple message appears until the operation is complete. However, the lengthy operation is called in a sequence of other operations, so the main thread would have to "stop and wait" until the background thread finishes as if everything was in one thread. Still, if I simply displayed a dialog box and then go on processing, the program window would not be redrawn until the lengthy operation is completed.

To avoid a major redesign of existing code I made it work like this:

1. My code calls the DoModal() method of a dialog box displaying a "Please wait..." prompt (say: CPatience). DoModal() gives the "illusion" of a single-threaded operation.

2. In OnInitDialog() of CPatience I start a background thread to do lengthy processing (i.e. call StartBackgroundTask()).

3. After the lengthy operation is finished I call EndDialog(IDOK) of CPatience (from RunBackgroundTaskProc()).

It seems to work. Do you think it is ok or is there a major design-flaw in my logic?

Best regards,

Maciej.