C / C++ / MFC

20-Mar-03 7:43

Hello,

INTRODUCTION
I'm using HTMLView in order to show the user a better and intuitive GUI.

I'm modifying the contents of the HTML page dinamically, and in order to avoid to write to disk each time that I want to make a modification, I modify the contents directly from memory.

I don't know how to create a new HTML document, so I must make the first navigation in a standard way before to modify the contents. (I've not been able to do it Blush | :O

). In order to create the document I use one of those methods:

<code>1.</code> this->Navigate2(_T("about:blank"), navNoHistory);
<code>2.</code> this->LoadFromResource(_T("IDR_HTML1"));

The code that I use in order to modify the HTML content dynamically (after the creation via the previous 1 or 2 method) is the next one:

<code>3.</code>
lpDispatch = this->GetHtmlDocument();

	if (lpDispatch)
	{
		hr = lpDispatch->QueryInterface(IID_IHTMLDocument2, (LPVOID*)&pHTMLDoc2);
		lpDispatch->Release();

		if (!SUCCEEDED(hr))
		{
			bRetorn = false;
		}
		else
		{
			pSafeArray = ::SafeArrayCreateVector(VT_VARIANT, 0, 1);
			
			if (pSafeArray)
			{ 
				hr = ::SafeArrayAccessData(pSafeArray,(LPVOID*) &pElement);
			
				if (!SUCCEEDED(hr))
				{
					bRetorn = false;
				}
				else
				{
					pElement->vt				= VT_BSTR;
					pElement->bstrVal		= csHTML.AllocSysString();

					hr = SafeArrayUnaccessData(pSafeArray);

					if (!SUCCEEDED(hr))
					{
						bRetorn = false;
					}
					else
					{
						pHTMLDoc2->clear();
						pHTMLDoc2->close();

						hr = pHTMLDoc2->write(pSafeArray);
						
						if (!SUCCEEDED(hr))
						{
							bRetorn = false;
						}
					}

					SysFreeString(pElement->bstrVal);
				}

				if (pSafeArray) SafeArrayDestroy(pSafeArray);
			}

			if (pHTMLDoc2) pHTMLDoc2->close();
		}
	}

QUESTION
I have used the perfmon Win2k utility [(Control Panel >> Administrative tools >> ...) or (executing directly "perfmon")] in order to find out if my code has memory leaks or handle leaks.

Calling the previous portions of code (1., 2., and 3.) leak some handles.

I would like to know why this is happening and how to avoid this.

NOTES
NOTE 1:
In order to see this I've used perfmon and I've added a new graph:
1. I've selected type "process".
2. I've selected "my process".
3. I've selected "Handles amount".

NOTE 2:
If I comment the code (1., 2. and 3.), there are no handle leaks (the handle leaks disappear).

As always thank you in advance.

Stephane Rodriguez.20-Mar-03 8:19

20-Mar-03 8:19

With this line in your code,

lpDispatch->Release();

you are freeing the document before you use it. Nice!

A suggestion is to use a smart pointer instead, in order not to have to manage the interfaces life cycle yourself :

CComQIPtr<IHTMLDocument2> pHtmlDoc( GetHtmlDocument() );

Joan M20-Mar-03 8:44

20-Mar-03 8:44

Well, I've changed the code as you've suggested, but the handle leaks are even faster than before... (I'm sure that it is my fault because it's the first time that I use this kind of pointers and that I work with HTMLViews...). This is the code:

CComQIPtr<IHTMLDocument2> pHtmlDoc(this->GetHtmlDocument());

	if (pHtmlDoc)
	{
		pSafeArray = ::SafeArrayCreateVector(VT_VARIANT, 0, 1);
		
		if (pSafeArray)
		{ 
			hr = ::SafeArrayAccessData(pSafeArray,(LPVOID*) &pElement);
		
			if (!SUCCEEDED(hr))
			{
				bRetorn = false;
			}
			else
			{
				pElement->vt				= VT_BSTR;
				pElement->bstrVal		= csHTML.AllocSysString();

				hr = SafeArrayUnaccessData(pSafeArray);

				if (!SUCCEEDED(hr))
				{
					bRetorn = false;
				}
				else
				{
					pHtmlDoc->clear();
					pHtmlDoc->close();

					hr = pHtmlDoc->write(pSafeArray);
					
					if (!SUCCEEDED(hr))
					{
						bRetorn = false;
					}
				}

				SysFreeString(pElement->bstrVal);
			}

			if (pSafeArray) SafeArrayDestroy(pSafeArray);
		}

		pHtmlDoc->close();
	}

In the other hand, and using the first code (the posted in the first question) I've changed two things (and this is how the code is working now):

lpDispatch = this->GetHtmlDocument();

if (lpDispatch)
{
    hr = lpDispatch->QueryInterface(IID_IHTMLDocument2, (LPVOID*)&pHTMLDoc2);

    if (!SUCCEEDED(hr))
    {
        bRetorn = false;
    }
    else
    {
        pSafeArray = ::SafeArrayCreateVector(VT_VARIANT, 0, 1);

        if (pSafeArray)
        {
            hr = ::SafeArrayAccessData(pSafeArray,(LPVOID*) &pElement);

            if (!SUCCEEDED(hr))
            {
                bRetorn = false;
            }
            else
            {
                pElement->vt             = VT_BSTR;
                pElement->bstrVal        = csHTML.AllocSysString();

                hr = SafeArrayUnaccessData(pSafeArray);

                if (!SUCCEEDED(hr))
                {
                    bRetorn = false;
                }
                else
                {
                    pHTMLDoc2->clear();
                    pHTMLDoc2->close();

                    hr = pHTMLDoc2->write(pSafeArray);

                    if (!SUCCEEDED(hr))
                    {
                        bRetorn = false;
                    }
                }

                SysFreeString(pElement->bstrVal);
            }

            if (pSafeArray) SafeArrayDestroy(pSafeArray);
        }

        if (pHTMLDoc2) pHTMLDoc2->close();
    }

    pHTMLDoc2->Release(); <code>this is new...</code>
    lpDispatch->Release(); <code>this is what I've moved...</code>
}

Using this version the problems are exactly the same than the ones that I've found in the first release...

Could you give me an idea on how to continue working? my customer has already seen the program and this program has to work 24 hours a day, this means that I cannot go back to plain texts and that I must find the solution...

Thanks a lot in advance...

Stephane Rodriguez.20-Mar-03 9:19

20-Mar-03 9:19

I would remove the clear() and close() method calls, since the only thing that matters is the write() method.

Joan M20-Mar-03 20:35

20-Mar-03 20:35

Well, thank you, I've done it and it continue working, but it continue leaking some handles...

I have more information to give to you:

The third code portion (step 3.) doesn't seems to be the guilty: that HTMLView modify it's contents each time the user selects items in a listView.

The HTML is used in order to show information regarding to items of a ListView, so each time that the user changes the selection the HTML gets changed...

The fact is that when the user changes the HTML View via selecting another field, nothing happens (I don't leak any handle).

but the first time the leaking occurs...

It seems that I create the new page via "Navigate2(_T("about:blank"));" and that when after I try to modify it I don't do it allright, because then and only then is when the leaks happen:

PROGRAM FLOW WHEN LEAKING HAPPEN:
1. this->Navigate2(_T("about:blank"), navNoHistory); <code>This line ONLY happens at the intitialization of the view...</code>
2. Selecting programatically the first item in the listview.
3. OnItemchanged calls PrepareHTML(); (Only one time (I'm sure about it))
4. PrepareHTML(); contains the <code>step 3</code> (the one you've helped me to modify...)
5. Closing window.

PROGRAM FLOW WHEN LEAKING HAPPEN 2:
1. this->Navigate2(_T("about:blank"), navNoHistory); <code>This line ONLY happens at the intitialization of the view...</code>
2. Selecting programatically the first item in the listview.
3. OnItemchanged calls PrepareHTML(); (Only one time (I'm sure about it))
4. PrepareHTML(); contains the <code>step 3</code> (the one you've helped me to modify...)
5. the user selects n times other items in the listview. <code>see notes below "note 1"</code>
6. Closing window.

NOTES:
note 1:
It's curious to see that the same handles are leaked if the user selects 2000 different items in the listview or if the user doesn't select any other item than the first one that is selected.

note 2:
If I comment the line that writes the safearray inside the HTML (inside the step 3)(hr = pHTMLDoc2->write(pSafeArray);) then no leaks happen.

note 3:
notes 1 and 2 make me think that I have misunderstood something in the middle of the steps 1 and 3 because the leaking only happen between those steps...
I've noticed that leakage only happens when I create the HTML page using Navigate2 and when after I Write a safearray inside the HTML page... leakage doesn't happen if, after the first time I select n items in the listview, in this case the HTML modification happens without any error...

As always thank you in advance.

Stephane Rodriguez.20-Mar-03 21:17

20-Mar-03 21:17

I don't know what might be the point of doing Navigate2("about:blank"). I don't think it is necessary. After all, once the underlying web browser instance is running, there is a default document to write to.

Joan M20-Mar-03 22:09

20-Mar-03 22:09

I thought this, but when I try to get the document the lpdispatch is not ready...

I would not do this if I would know how to create and attach a document to the CHTMLView...

But meanwhile...
Time to say that the HTMLView is not a normal HTMLView...
It's a HTMLCtrl, a wrapper class written by Paul DiLascia that makes possible to insert a HTMLView inside a dialog.
But before posting the question here in CP, I wrote down to Mr. DiLascia in order to ask him about it and his answer was that it must be a error of the MFC because his class was just a wrapper...

If you want I can try to send you a little sample code in order to make easier to talk about the problem...

What do you think about me sending you a little sample of this?

If you don't want to receive my little sample (with all the needed modifications), you can also download his article and source codes from his site at: http://www.microsoft.com/msj/0100/c++/c++0100.asp[^]

Note:
The DiLascia's article doesn't modify dynamically the web page contents.

Thanks a lot in advance for your time and help.

Stephane Rodriguez.20-Mar-03 22:31

20-Mar-03 22:31

Ok then, to spend as little time as possible with the handle leak issue, the first thing to do is to isolate the code. This is a general debugging rule, and it translates in your particular case by trying to reproduce the behaviour with a simple CHtmlView class.
Good luck!

Joan M20-Mar-03 22:53

20-Mar-03 22:53

I have a little sample ready, can I send it to you? it's really simple:
2 dialogs and 3 buttons...

What do you think about it?

Thank you in advance.

Joan M20-Mar-03 22:59

20-Mar-03 22:59

Hello,

I'd like to tell you that I'm very sorry to annoy you with my problems... I don't like to do it, but I need to solve those problems as fast as I can... the program is now installed in an industrial PC that controls a machine and after some hours the PC crashes...

I hope that after seeing the little program you'll be able to tell me how stupid I've been to pass a surely easy thing...

As I said before (in other post) I'm dealing with those pointers and HTML for first time...

Thank you in advance, and please, if you don't want me to send you the sample, feel free to tell it to me, you've been trying to help me for a long time and I don't want to annoy you more...

Joan M21-Mar-03 4:05