GetDC() is leaking memory?

[timmay3141]

In a program I'm working on (the same program that was causing me trouble a couple months ago that I posted about then, if you remember), I have a thread similar to this. It does more, but I have left out the unimportant parts:

UINT MyViewClass::HandleThread(LPVOID lp)
{
MyViewClass* pView = (MyViewClass*)lp;
MyDocClass* pDoc = pView->GetDocument();

while(1)
{
CDC* pDC = pView->GetDC(); // Line 8
pDoc->DrawStuff(pDC); // Line 9
::Sleep(100);
}

return 0;
}

Using the Stress Utility, I've managed to find the source of the problems. When I leave it as is, the GDI32 drops drastically, along with the User % and to a lesser extent the GDI%. When I comment out line 9, it doesn't help at all. However, when I comment out the lines 8 and 9, I don't lose anything. I took this to mean that the repeated GetDC calls are reaking havoc on my system (it lags really bad after a while). What is the problem, and what can I do to fix it?

 

[qednick]

remove line 8 and don't pass a CDC* to DrawStuff(). Instead, obtain the CDC* within the DrawStuff() function and perform the necessary clean ups there.

^{programmer (prog'ram'er), n A hot-headed, anorak wearing, pimple-faced computer geek.}​

 

[Zyrenthian]

Do you restore the dc when your done? When you select an object into the dc, it will return a pointer to it's base object. If you dont re-select that back into the DC you will have leaks (99% sure of that cause I think it bit our butt here at work)

Matt

 

[qednick]

Like Matt said, those GDI based objects are notorious for causing memory leaks!

^{programmer (prog'ram'er), n A hot-headed, anorak wearing, pimple-faced computer geek.}​

 

[VincentP]

From MSDN's entry for ReleaseDC:

"The application must call the ReleaseDC member function for each call to the GetWindowDC member function and for each call to the GetDC member function."

So I recommend you add

pView->ReleaseDC(pDC);

after line 9.

I don't know if that is the source of your problem, but it can't hurt to try

Vincent

 

[timmay3141]

Thanks everyone for your responses. I'll fix it tomorrow and get back to you.

 

[timmay3141]

The ReleaseDC() fixed it. Thanks for your advice, everyone.