C / C++ / MFC

31-May-04 9:30

Hi,

I have a multi-threaded OCX (MFC) - which spawns 5 worker threads at a time, for a list of jobs. I am using WaitForMultipleObjects() with the handles of the 5 threads to wait until any of the thread finishes. As soon as WaitForMultipleObjects() returns, that thread is reused for the next job in the queue.

I need to know how do I check if the handle of a given thread is valid or not! When a given thread "ends", its handle is NOT always NULL, and so cannot be checked as:

if(m_pthJob[nItr]->m_hThread == NULL)

Could you please guide me how to check if the handle is valid or invalid?

Thanks,

Nirav Doshi

* Don't wish it was easier, wish you were better! *

Michael Dunn31-May-04 12:26

Michael Dunn

31-May-04 12:26

When you create a thread, you get a handle back. That handle remains valid until you explicitly close it (or your process exits, but by that time it's too late to use the handle). The handle remains valid even after the thread exits, because the thread object in the kernel doesn't go away until all handles on it are closed. When a thread exits, your handles don't magically become null.
If your handle is becoming invalid (is WaitForMultipleObjects() returning an error?) then you're doing something else wrong with the handles.

--Mike--
Personal stuff:: Ericahist | Homepage
Shareware stuff:: 1ClickPicGrabber | RightClick-Encrypt
CP stuff:: CP SearchBar v2.0.2 | C++ Forum FAQ
----
I even hear the Windows "OMG I booted up fine" sound.
-- Paul Watson diagnosing hardware problems.

Nirav Doshi31-May-04 20:39

31-May-04 20:39

Michael Dunn wrote:
If your handle is becoming invalid (is WaitForMultipleObjects() returning an error?)

Yes!

I'll explain here:

Suppose I have 12 jobs. Since my MAX_THREADS is 5, 7 jobs are pending the first time WaitForMultipleObjects() is called. As and when my WaitForMultipleObjects() returns, I get back to assigning another job to that (returned) thread. I have another small loop just before calling WaitForMultipleObjects() where I an checking if by the time I was assigning another job to the first thread that returned, if any other thread has finished. To find if any other thread has finished working till I am assigning another job, I am checking if the thread handle is valid/invalid. Here I am getting the thread handle sometimes as NULL (0x00000000) or some junk (0xfeeeeeee, etc.) so I am unable to check for it.

I have another method (which I didn't really like!), which is using a thread variable to give the current thread state. But I hope, there's some way to check if the thread handle is valid/invalid.

Thanks,

Nirav Doshi

* Don't wish it was easier, wish you were better! *

Diddy1-Jun-04 1:54

Diddy

1-Jun-04 1:54

How are you starting your threads?

If you are using AfxBeginThread (and looking at m_pthJob[nItr]->m_hThread, it looks if you are), I suspect you are being plauged by MFC's auto deleting thread system.

Make sure you set the m_bAutoDelete member of the returned thread to FALSE before starting the thread (create it in a suspeded state). The thread handle will then remaing valid, even after the thread is finished. If it is running, WaitForSingleObject(hThread, 0) will give you WAIT_OBJECT_0, if not, it will give you WAIT_TIMEOUT.

Remeber to then delete your CWinThread's manually

Or, use DuplicateHanlde to copy the m_hThread handle from the real WinThread to someewhere else - then clean up using CloseHandle.

Nirav Doshi1-Jun-04 2:13

1-Jun-04 2:13

Hello Diddy,

You're right about the thread being deleted automatically since I'm not setting the AutoDelete flag to FALSE! But I was doing it expecting the thread handle to be set to NULL when the thread finished - or something which gave me a response that the thread is done working.

So, how would I then get to know if a thread is not running ((hopefully) without using a variable/flag)? I need to check if a given thread is currently finished or still working.

Thanks,

Nirav

* Don't wish it was easier, wish you were better! *

Diddy1-Jun-04 5:10

Diddy

1-Jun-04 5:10

To check if a thread is running:

CWinThread* pThread = ....

if(::WaitForSingleObject(pThread->m_hThread, 0) == WAIT_OBJECT_0))
{
// thread is running
}
else
{
// thread has finished
}

The other way is also:

if(::GetExitCodeThread(pThread->m_hThread, &dwExit) != 0 && dwExit == STILL_ACTIVE)
{
// thread is running
}
else
{
// thread has finished
}

But the first is usually prefered.

With both, you must be careful you are working with a valid thread handle. FYI there are 2 ways (that i know of) to be sure you have a vaid handle with MFC threads:

Autodelete - default
---------------------
CWinThread* pThread = ::AfxBeginThread(...);

This way, as you have discovered, you can't do anything with the pThread as MFC can delete it at any time. After the above thread has been started, doing pThread-> is ALWAYS a risky bit of code. You don't know when MFC will kill off your CWinThread object, and you could be refering to a bit of memory that has just been deleted.

DuplicateHandle
----------------
CWinThread* pThread = ::AfxBeginThread(...CREATE_SUSPENDED);
HANDLE h;
::DuplicateHandle(pThread->m_hThread, h, ...);

This works because handles are refrenced counted. The DuplicateHanld call bumps this count up to 2 and puts a copy in 'h', so when CWinThread autodeletes and does a CloseHandle on it's m_hThread member, the handle isn't realy closed until you do a CloseHandle on 'h'. Don't be tempted to do this:

CWinThread* pThread = ::AfxBeginThread(...CREATE_SUSPENDED);
HANDLE h = pThread->m_hThread;

As your count will still only be at 1.

m_bAutoDelete = FALSE;
----------------------
As shown above, this is usually the easiest. Just delete your CWinThread* and that will close your thread handle.

Nirav Doshi1-Jun-04 8:03

1-Jun-04 8:03

Thank you very much Diddy for taking the efforts to explain this! Rose | [Rose]

I've taken note about your DuplicateHandle() point! Thanks!

I'm now changing a majority of my processor code & logic. I guess, using a variable which gives me the current state of each of my threads is the best work-around for my problem. D'Oh! | :doh:

Working on it... Unsure | :~

Thanks again to you and Micheal for your replies. Cool | :cool:

Hope I could be able to help you both here someday!

- Nirav Doshi

* Don't wish it was easier, wish you were better! *

Re: Costom Draw Problem!!!

Diddy1-Jun-04 10:27

Diddy

1-Jun-04 10:27

No problem Smile | :)

Costom Draw Problem!!!

VirgoCI31-May-04 8:24

VirgoCI

31-May-04 8:24

<virgoci> guys. is there anyone here with an extended knowladge of MFC?
<virgoci> i am having problems with making a CToolBarEx control.
<virgoci> it's derived from CToolBar
<virgoci> for some crapy reason i can't find a way to override the painting funcs! i mean i found a few ways to do so but all those ways are bad since they all have some flaws.
<virgoci> i tried using OnUpdateCmdUI() but it is flawed as well cuz it draws the saparator buttons but since this func called after the actual drawing proccedure the grafics sometimes glich alot.
<virgoci> i found OnNMCustomdraw() a good way to do owner drawing but there is a flaws in it.
<virgoci> for some reason i can't draw the speretor buttons using that func! and even when the windows calls this func with the CDRF_NOTIFYITEMDRAW message it skips the seperator buttons. i even tried to out smart it and detect and draw the seperator buttons when it calls the func with CDDS_PREPAINT which means it redraws the whole toolbar but it seems it's smarter then i am cuz when i draw something at the location of the seperator buttons it would draw it as a back ground and still draw the damn windows`s 3d Line as a seperator!
<virgoci> anyone know of anything that can help me?

plz mail me if you have a solution for me...
virgoci@mail.ru

Antti Keskinen31-May-04 11:46

Antti Keskinen

31-May-04 11:46

For just about complete control: Capture WM_PAINT messages.

Using this mode, however, you need to paint everything yourself. Familiarize yourself with the Platform GDI commands, which allow you to paint just about everything from lines to edges and to rectangles. Heck, you can even draw a standard button by using DrawEdge().

It takes time to make it completely custom drawn, but once you have accomplished this once, you are a BIG LEAP forward on learning how to make even more customized controls. I suggest taking this trip, as it will prove most fruitfull.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

Re: Costom Draw Problem!!!

VirgoCI31-May-04 17:48

VirgoCI

31-May-04 17:48

thanks antti. i tried to refrain of using WM_PAINT cuz i knew i will have to redraw the whole ctrl from scratch. (i am abit lazy)
oh well... guess it's "build it your self in 21 From Scratch" time. Big Grin | :-D

smtp question

includeh1031-May-04 8:16

Problem with SetTextColor

31-May-04 8:16

we sent our customers emails by smtp for 4 times in 2 months, by several university customers complained that they didn't receive our emails.

we guess the reason is that smtp servers of universities don't accept our emails because we are not in their mail list - is this right?

thanks

includeh10

Re: smtp question

bryce31-May-04 15:10

bryce

31-May-04 15:10

you would have to ask the universities, if your other customers all received their emails and the uni people didnt it would seem you emails might be getting tagged at spam
bryce

---
Publitor, making Pubmed easy.
http://www.sohocode.com/publitor

Aviv Halperin31-May-04 7:50

Aviv Halperin

31-May-04 7:50

Hi,

I have a dialog with a few edit controls.
I want to set the text of one control to red and the rest should not change.

Now if I call the pDC->SetTextColor(RGB(255,0,0)) in the OnCtlColor message handler of the dialog this changes the text color for all the edit controls in the dialog.

If I call the following code:
CDC *pDC = EditToChangeTextColor.GetDC();
pDC->SetTextColor(RGB(255,0,0));

nothing changes.

Does anyone know if there is a way to change the text collor only for one control in the dialog?

Thanks.

avivhal

Brian D31-May-04 8:15

Brian D

31-May-04 8:15

How about surrounding the call with:

if(pWnd->GetDlgCtrlID() == IDC_EDIT1)

or switch the results out.

BD

"You know "that look" women get when they want sex? Me neither."

--Steve Martin

includeh1031-May-04 8:21

31-May-04 8:21

it is not correct.
you must call SetTextColor() inside of OnPaint() of your control

includeh10

f6431-May-04 8:22

f64

31-May-04 8:22

Hi Check the MSDN fot CWnd::OnCtlColor, it even has a example of what you are asking. You just have to verify the message is for the control you want to change, otherwise do nothing.

Extracted form the MSDN

// This OnCtlColor handler will change the color of a static control
// with the ID of IDC_MYSTATIC. The code assumes that the CMyDialog
// class has an initialized and created CBrush member named m_brush.
// The control will be painted with red text and a background
// color of m_brush.

HBRUSH CZilchDlg::OnCtlColor(CDC* pDC, CWnd* pWnd, UINT nCtlColor) 
{
   // Call the base class implementation first! Otherwise, it may
   // undo what we're trying to accomplish here.
   HBRUSH hbr = CDialog::OnCtlColor(pDC, pWnd, nCtlColor);

   <big>// Are we painting the IDC_MYSTATIC control? We can use
  // CWnd::GetDlgCtrlID() to perform the most efficient test.</big>   
   if (pWnd->GetDlgCtrlID() == IDC_MYSTATIC)
   {
      // Set the text color to red
      pDC->SetTextColor(RGB(255, 0, 0));

      // Set the background mode for text to transparent 
      // so background will show thru.
      pDC->SetBkMode(TRANSPARENT);

      // Return handle to our CBrush object
      hbr = m_brush;
   }

   return hbr;
}

Fabian

documentation of jpeg format

Aviv Halperin31-May-04 9:16

Aviv Halperin

31-May-04 9:16

Thanks now its working fine,
I dont know how I missed this example in the MSDN (should have thought of it myself anyway), I only found a very general one with no reference as to the caller.
Is it possible maybe to call SetTextColor from outside OnCtlColor?
I tried it in various places and handlers but it did not seem to work(including in the OnPaint handler).
Maybe the attributes set for the DC fonts color are blocked when called from outside this segment of code...

Thanks again.

avivhal

includeh1031-May-04 6:54

Re: documentation of jpeg format

31-May-04 6:54

hi all,

i need good docs about jpeg format, i have to create my own file format for compressing bmp file based on jpeg.
all i have are poor jpeg docs from internet.

thanks for any link to better docs of jpeg format
cheers

includeh10

Nirav Doshi31-May-04 9:11

Re: documentation of jpeg format

31-May-04 9:11

Try:
The Programmer's File Format Collection.

http://www.wotsit.org/[^]

* Don't wish it was easier, wish you were better! *

includeh1031-May-04 9:49

Re: documentation of jpeg format

31-May-04 9:49

it looks useful.
thanks

includeh10

Nirav Doshi31-May-04 22:23