C / C++ / MFC

13-Dec-07 19:07

I am doing a TankGame program,and I write a CBullet class.I write a thread function to make it move when it is created:

UINT BulletGo(LPVOID pParam)
{
CBullet* bullet=(CBullet*)pParam;
while(TRUE)
{
switch(bullet->m_bCanGo.GetDirection())
{
case UP:
bullet->GoUp();
break;
case DOWN:
bullet->GoDown();
break;
case LEFT:
bullet->GoLeft();
break;
case RIGHT:
bullet->GoRight();
break;
}
if(!bullet->m_bCanGo)
break;
else
bullet->MoveWindow(bullet->GetPosition().x,
bullet->GetPosition().y,
bullet->GetThisRect().Height(),
bullet->GetThisRec().Width());
Sleep(30);
}
return 0;
}

int CBullet::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
if (CStatic::OnCreate(lpCreateStruct) == -1)
return -1;

m_bCanGo=TRUE;
m_pThread=AfxBeginThread(BulletGo,this); //begin thread

return 0;
}

BOOL CBullet::GoDown()
{
if((m_ptPosition.y+m_rtThis.Height())>m_rtParent.bottom)
{
m_ptPosition.y+=2;
m_bCanGo=TRUE;
return TRUE;
}
else
{
this->DestroyWindow();
m_bCreated=FALSE;
m_bCanGo=FALSE;
return FALSE;
}
}

When the bullet go down and hit the bottom of client rect the program apprear errors.Why...Don't the "break" in the BulletGo() end the thread?

Llasus13-Dec-07 19:21

Llasus

13-Dec-07 19:21

what exactly is the error?

Chen-XuNuo14-Dec-07 4:32

14-Dec-07 4:32

The application pops up a dialog about error saying that Debug Assertion Failed!
Program : D:\Code\TankGame\Debug\TankGame.exe
File : wincore.cpp
Line : 304
......

Mark Salsbery13-Dec-07 19:23

13-Dec-07 19:23

You need to synchronize the shutdown a bit better.

By the time you set m_bCanGo=FALSE you've destroyed the window,
yet your thread is still doing (attempting) operations on it.

Try something like this:

BOOL CBullet::GoDown()
{
    if((m_ptPosition.y+m_rtThis.Height())>m_rtParent.bottom)
    {
        m_ptPosition.y+=2;
        m_bCanGo=TRUE;
        return TRUE;
    }
    else
    {
<code>        m_bCanGo=FALSE;
        ::WaitForSingleObject(m_pThread, INFINITE);
</code>
        this->DestroyWindow();
        m_bCreated=FALSE;
        return FALSE;
    }
}

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Chen-XuNuo14-Dec-07 4:34

14-Dec-07 4:34

Thank you for you advice.But it helps nothing to the problem... Sigh | :sigh:

Mark Salsbery14-Dec-07 4:58

14-Dec-07 4:58

If that's the case, then you need to debug.

Can you post more specifics on the problem? Does it crash?
If so, on what line? If not, does the thread ever exit?
If not, why? Use breakpoints and single step to find out.
Etc...

Running in the debugger you should be able to find what line of
code is causing problems and trace back to why there's a problem.

Your original code is not going to work correctly. You
MUST manage synchronization of your threads!

Also, using a separate thread doesn't mean less CPU cycles are used,
as implied by your post below. One thread per moving object will start
to degrade performance once you have many objects going at once.
Plus it's wasteful of resources. Even one thread on a modern PC is
capable of tracking and rendering MANY moving objects.

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Chen-XuNuo14-Dec-07 18:03

14-Dec-07 18:03

I set a breakpoint on "return 0" in the thread function.When the bullet hit the bottom of client rect,the appliction jump to the breakpoint,and I step over,the debugger doesn't pop up error dialog until execute to the line AfxEndThread(nResult) in function UINT APIENTRY _AfxThreadEntry(void* pParam).
How do you think the two methods of conrol the enemies and bullets that one use threads and the other use timer in class?Which waste more CPU resource?

Mark Salsbery15-Dec-07 7:45

15-Dec-07 7:45

Chen-XuNuo wrote:
How do you think the two methods of conrol the enemies and bullets that one use threads and the other use timer in class?Which waste more CPU resource?

Total CPU usage is going to be pretty close to the same with either
method, up to a point.

At some point, you can have so many threads that the system is
spending too much time switching between them. That will degrade
performance.

There's nothing wrong with what you're doing, except scaleability.
If you decide to be able to have hundreds of bullets being animated
at the same time, you can still do that with one thread. There's no
good reason to have a separate thread for each bullet.

A fairly easy scenario for a simple game would have:

1) One thread that does ALL the drawing/rendering. This eliminates the
problems with GDI/DirectX/etc. synchronization between threads. You
can synchronize them, but that slows it down - waiting threads are doing
nothing when they could be working Smile | :)

This thread could be awakened by
a multimedia timer event to provide a smooth animation frame rate.

2) A second thread to do all the calculations of bullet positions and
movement of other objects. The information calculated by this thread
would be used by the rendering thread so it knows where to draw stuff.
If coded efficiently,, the render thread should be able to read the info
it needs without ever waiting on this thread.

Of course, there's an infinite number of ways to design this.
My point is that you can do a LOT of processing with very few threads
on modern PCs Smile | :)

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Chen-XuNuo14-Dec-07 18:15

14-Dec-07 18:15

I have found the error:I can't end the thread after destorying the window,right? Poke tongue | ;-P

Mark Salsbery15-Dec-07 7:33

15-Dec-07 7:33

Chen-XuNuo wrote:
I can't end the thread after destorying the window,right?

Right

Not if the thread is using the window!

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Chen-XuNuo15-Dec-07 3:14

15-Dec-07 3:14

I am going to be crazy.. Dead | X|

The problem still haven't been solved.
UINT BulletGo(LPVOID pParam)
{
CBullet* bullet=(CBullet*)pParam;
while(TRUE)
{
switch(bullet->GetDirection())
{
case UP:
bullet->GoUp();
break;
case DOWN:
bullet->GoDown();
break;
case LEFT:
bullet->GoLeft();
break;
case RIGHT:
bullet->GoRight();
break;
}
if(!bullet->m_bCanGo)
break;
else
bullet->MoveWindow(bullet->GetPosition().x,bullet->GetPosition().y,
bullet->GetThisRect().Height(),bullet->GetThisRect().Width());
Sleep(30);
}
return 0;
}
BOOL CBullet::GoDown()
{
if(m_rtParent.bottom==0)
GetParent()->GetClientRect(&m_rtParent);
if((m_ptPosition.y+m_rtThis.Height())<m_rtParent.bottom)
{
m_ptPosition.y+=6;
m_bCanGo=TRUE;
return TRUE;
}
else
{
m_bCreated=FALSE;
m_bCanGo=FALSE;
while( ::WaitForSingleObject(m_pThread->m_hThread,1) == WAIT_TIMEOUT)
{
Sleep(1);

}
delete m_pThread;
this->DestroyWindow();
return FALSE;
}
}
I destroy the window after ending the thread.
Is the judgement:
::WaitForSingleObject(m_pThread-&gt;m_hThread,1) == WAIT_TIMEOUT
right?If it is right,where is the problem.. Cry | :((

Mark Salsbery15-Dec-07 7:31

15-Dec-07 7:31

Chen-XuNuo wrote:
::WaitForSingleObject(m_pThread->m_hThread,1) == WAIT_TIMEOUT

That should work fine, although you really don't need to loop.

A simple

::WaitForSingleObject(m_pThread->m_hThread, INFINITE);

should be good enough.

Chen-XuNuo wrote:
delete m_pThread;

This isn't good. CWinThread objects delete themselves by default.
If you delete it twice, whichever delete happens last is going to crash!
You probably should remove that line Smile | :)

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Chen-XuNuo15-Dec-07 14:52

15-Dec-07 14:52

Thank you very much.The problem has been solved. Rose | [Rose]

Cedric Moonen13-Dec-07 20:26

Cedric Moonen

13-Dec-07 20:26

If you want my advice, I don't think that you need to create a thread for that. If you keep that logic, it would mean that you will create a thread for every bullet in your game. And probably for every ennemy too. Honnestly, I don't think this is a good idea.

You should better process the position of all your 'entities' (bullets, ennemies, ...) in the message pump and then draw everything on the screen. You don't need a thread for that.
I don't know if you are using the MFC's or not, but if that's the case, then you won't have access to the message pump. But you could override the OnIdle function from your App class and do it there.

Cédric Moonen
Software developer

Charting control [v1.2]

Mark Salsbery13-Dec-07 20:38

13-Dec-07 20:38

OnIdle...bleh. I'd prefer a multimedia timer for smoother frame rate Smile | :)

Cheers

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Chen-XuNuo14-Dec-07 4:40

14-Dec-07 4:40

Mmmm...I think if I draw the 'entities' with DC,I think the application would take large CPU resource,so I do it in thread.And I think using thread to control the enemies and the bullets easier.
I will try you advice, thank you~

C2365 error

subramanyeswari13-Dec-07 18:54

subramanyeswari

13-Dec-07 18:54

I am exporting two functions. Cleanup and close.
extern "C" __declspec(dllexport) BOOL Cleanup(VOID)
and
extern "C" __declspec(dllexport) BOOL Close(VOID)

In the Cleanup function i am calling Close() method.

if ( temp.lpLocalData->hComm != INVALID_HANDLE_VALUE ) {
Close();

}

This resulted in two compiler error
error C3861: 'Close': identifier not found and
error C2365: 'Close' : redefinition; previous definition was 'formerly unknown identifier'

How to call Close in Cleanup function?

Re: C2365 error

Mark Salsbery13-Dec-07 19:13