multi-thread win32 programming

[robig2]

hi,

im trying to get a part of my program as a new thread. now, i know i need to define the thread as:

 void ThreadName( void* pParams )

and start it with

 
    long handle,code;
    handle=_beginthread( Thread, 0, NULL );

but since the thread is a special kind of function, i need to pass several vars to it except that i dont know how... can anyone please explain this? or point me to a tutorial about this?

im programming in C

[Elysia]

It's easy, really.
If you know what you're passing, you can easily cast it back:

void MyThread(void* pParam)
{
	int n = (int*)pParam;
}

int main()
{
	int n = 100;
	_beginthread(&MyThread, 0, &n);
	return 0;
}

If you need to pass more than argument, use a struct, then create the struct, fill it with information and pass it along.
However, I must warn you that you should not be passing data to a thread that will be used by both the new thread and the main thread at the same time. Only one thread should use the data; otherwise you'll be walking into deeper waters.

[robig2]

i thank you very much!
i`ll go try it out now

[robig2]

well... it became too complex... ive noticed that some globar vars are being used throughout my program and so i`ll have to synchronise between too many sections... not worth it.
but at least ive learned sometihng! thanks again

[Elysia]

Avoid global variables! They are not thread safe, sometimes they aren't optimized and they are hard to keep track of and easily creates bugs!
Just an advice for you.

[robig2]

im talking bout my window handles.
i wanted to use the new thread to resize my childwindows but im also using the child windows at other places of the main thread so all i get instead is a great big access violation....................
i`ll abandon this course of action for now

[Elysia]

You can easily pass data to threads if they receive a local copy or make a local copy. As long as two threads aren't modifying the same data, all is fine.

void MyThread(void* pParam)
{
	HANDLE hMyHandle = (HANDLE)pParam;
}

int main()
{
	HANDLE hMyHandle; /* Assume it's a valid handle */
	_beginthread(&MyThread, 0, (void*)hMyHandle);
	return 0;
}

[robig2]

ok then,
how do i keep the program from running over the same thread? (since its being called from under WM_SIZE) i mean, if it gets back to WM_SIZE before the thread has ended, will it give me any trouble?

and do i need to use the _endthread(); command?

[Elysia]

ok then,
how do i keep the program from running over the same thread? (since its being called from under WM_SIZE) i mean, if it gets back to WM_SIZE before the thread has ended, will it give me any trouble?

Not sure what you mean. Do you expect a thread to do some work inside your window proc and end before the window proc ends?

and do i need to use the _endthread(); command?

You can use it to explicitly kill a thread, but it's not recommended. It will cause the thread's stack to be leaked and you can find your program in a zombie state since the thread can't clean up (what will happen if you kill it in the middle of updating something?).

[robig2]

Not sure what you mean. Do you expect a thread to do some work inside your window proc and end before the window proc ends?

well, yea. i want it to do all the MoveWindow calls that ive done under WM_SIZE so that it will happen faster and the screen wont blink when i resize the window.

		  case WM_SIZE:

// on every WM_SIZE msg to parent window, we want the children windows to resize as well

			  hdc = GetDC (hwnd) ;
			  GetTextMetrics (hdc, &tm) ;
			  ReleaseDC (hwnd, hdc) ;


						//rect.right is how wide the list window is
			   rect.right= 
						// new width of parent window				   
				   LOWORD(lParam) 
						// - size mod tmAveCharWidth to avoid letter clipping
				- (LOWORD(lParam)%tm.tmAveCharWidth) 
						// + vScrollSize
				+ vScrollSize 
						// - area dedicated for IDD_LIST_BUTTONS dialog				
				- tm.tmAveCharWidth*18;

						//calculates the size of one colume
			   rect.right=rect.right/4-rect.right%tm.tmAveCharWidth;

			   
						//rect.bottom is how high the list window is
			   rect.bottom= 
						// new height of parent window				   
				   HIWORD(lParam) 
						// - size mod tmHeight to avoid letter clipping
				   - (HIWORD(lParam)%tm.tmHeight) 
						// - Y position of list window to leave some empty space under it	
				   - tm.tmHeight * 3;



			   MoveWindow(hwndListFname,
				   tm.tmAveCharWidth, // 1 char from the left side of main window
				   tm.tmHeight * 3,   // 3 chars from the top side of main window
				   rect.right,
				   rect.bottom,
				   FALSE);
			   MoveWindow(hwndListLname,
				   tm.tmAveCharWidth+rect.right, // starts where 1st one stops
				   tm.tmHeight * 3,   // 3 chars from the top side of main window
				   rect.right,
				   rect.bottom,
				   FALSE);
			   MoveWindow(hwndListHphone,
				   tm.tmAveCharWidth+2*rect.right, // starts where 2nd one stops
				   tm.tmHeight * 3,   // 3 chars from the top side of main window
				   rect.right,
				   rect.bottom,
				   FALSE);
			   MoveWindow(hwndListCphone,
				   tm.tmAveCharWidth+3*rect.right, // starts where 3rd one stops
				   tm.tmHeight * 3,   // 3 chars from the top side of main window
				   rect.right,
				   rect.bottom,
				   FALSE);
			   MoveWindow(hwndListButtons,
				   4*rect.right+tm.tmAveCharWidth,
				   tm.tmHeight * 3,
				   13*tm.tmAveCharWidth,
				   8*tm.tmHeight, FALSE);
	return 0 ;

and ive changed it to this:

	case WM_SIZE:
			 EnterCriticalSection( &cs );
			 
			  
			   handle=_beginthread( MoveWindowThread, 0, NULL );
			 LeaveCriticalSection( &cs );

			   GetExitCodeThread(handle,&code);
			   ExitThread(code);
return 0 ;

where MoveWindowThread does all of the above. should i post it as well? i didnt coz i dont want to fill up with too much code....

oh, and ive just saw there is a CreateThread function for win32 progs... should i use that one instead?

[Elysia]

It doesn't work that way. Threads are meant to be functions executing in parallel with other code and not to take up some insignificant task and finish it before the other thread finishes.
In other words, threads are good for asynchronous work or parallel work, but not for synchronous work.

[robig2]

so its supposed to be used on an entirly independed part of the program?

in that case, i cant use it here....

[Elysia]

It's supposed to be used if you want code to execute in parallel (ie while you do task A, you also do task B and not first task A and then task B).

[robig2]

for example if i had 4 windows to move and i move each on at the same time on a diffrent thread. got it
any chance and you can answer my 2nd question about the blinking windows? or is it too complex? coz i dont have to do it but i would like to.....

[Elysia]

for example if i had 4 windows to move and i move each on at the same time on a diffrent thread. got it

Well, in theory, yes, but you need to be careful here.
On a single processor, threads are scheduled to it. So thread A executes for 10 ms, then thread B for 10 ms and so on. They don't actually execute in parallel. It's just an illusion that they do.
On multi-core systems, they actually do execute in parallel, but the theory behind your idea is sound.

any chance and you can answer my 2nd question about the blinking windows? or is it too complex? coz i dont have to do it but i would like to.....

Well, Windows programming is difficult. It's hard to say right out of the bat what's wrong.