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hi,
im trying to get a part of my program as a new thread. now, i know i need to define the thread as:
and start it withCode:void ThreadName( void* pParams )
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?Code:
long handle,code;
handle=_beginthread( Thread, 0, NULL );
im programming in C
It's easy, really.
If you know what you're passing, you can easily cast it back:
If you need to pass more than argument, use a struct, then create the struct, fill it with information and pass it along.Code:void MyThread(void* pParam)
{
int n = (int*)pParam;
}
int main()
{
int n = 100;
_beginthread(&MyThread, 0, &n);
return 0;
}
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.
i thank you very much!
i`ll go try it out now
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
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.
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
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.
Code: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;
}
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?
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?Quote:
Originally Posted by robig2
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?).Quote:
and do i need to use the _endthread(); command?
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.Quote:
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 ive changed it to this:Code: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 ;
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....Code:
case WM_SIZE:
EnterCriticalSection( &cs );
handle=_beginthread( MoveWindowThread, 0, NULL );
LeaveCriticalSection( &cs );
GetExitCodeThread(handle,&code);
ExitThread(code);
return 0 ;
oh, and ive just saw there is a CreateThread function for win32 progs... should i use that one instead?
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.
so its supposed to be used on an entirly independed part of the program?
in that case, i cant use it here....
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).
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.....
Well, in theory, yes, but you need to be careful here.Quote:
Originally Posted by robig2
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.
Well, Windows programming is difficult. It's hard to say right out of the bat what's wrong.Quote:
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.....
yes, it is difficult.. but ive seen it happen pretty much on every program me or any of my friends wrote so i though it was something to do with the time it takes the program to redrew everything on resize but then again on every commercial program it doesnt happen... so there must be something to be done. but thats ok for now. i can give it a rest and figure it out at another time.Quote:
Quote:
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.
This tutorial covers common causes and fixes for flickering windows.
http://catch22.net/tuts/flicker.asp
gg
Elysa, you are a programming noob, why the hell don't you know anything! :/Quote:
Originally Posted by Elysia
If you need to use a global variable with a thread, declare the varible as volatile.
Just be aware that multiple threads may access it at the same time. If two or more threads need to use a shared item, use CRITICAL_SECTION's.
Yeah, right :rolleyes:Quote:
Originally Posted by abachler
This was discussed before. Volatile is pretty much compiler implementation defined, unknown territory. And you don't need volatile if there's just one thread accessing it!Quote:
If you need to use a global variable with a thread, declare the varible as volatile.
Just be aware that multiple threads may access it at the same time. If two or more threads need to use a shared item, use CRITICAL_SECTION's.
If two threads are accessing it, THEN you need locks.
But this still makes them bad because of other reasons I pointed out. Some globals just aren't optimized, and they can create hard-to-maintain code in larger projects.
and for all the reasons that where discussed, globals are not inherently bad. People misuse globals just as they misuse templates or classes, that doesnt make them bad. Poor programming does not make a feature 'bad'. There are many times when globals can easily solve a problem that would otherwise be convoluted or quite frankly impossible to solve. Ultimately there will always be at least some data that MUST be global for any serious project to function. If I have 50 thread functions that all access a common database, I certainly do NOT want to maintain that database seperately for each thread. The simple solution is a global variable. If someone has problems reading -Quote:
Originally Posted by Elysia
then they shouldnt be programming in the first place. If they cant find the initial declaration, perhaps they need to check oh, I dont know 'declarations.cpp' or some such.Code:extern LPVOID pDatabase;
Crappy programmers shouldn't breathe, that would save us all a lot of problems with people crying about global variables. If you cant handle globals, or you can't use them properly, then don't use them, but don't make high and mighty claims that they are therefore 'BAD'.
IMO it is a very bad idea to have two threads running on the same UI. Most controls are not thread safe.
One thing it misses is to use bothQuote:
Originally Posted by Codeplug
InvalidateRect();//set area to be redrawn
UpdateWindow();//bypass the OS message queue and post directly to the windows callback
This makes the paint message non-queued for faster drawing (as paint messages will be ignored and concatenated in the OS msg queue).
I believe "this" is in reference to the use of volatile. The volatile keyword has nothing to do with multi-threaded programming....unless your compiler says it does (I only know of one compiler that does).Quote:
Originally Posted by Elysia
Discussed before here:
http://cboard.cprogramming.com/showthread.php?t=97344
http://cboard.cprogramming.com/showthread.php?t=97475
gg
I do agree, but usually they are misused. If they didn't have a purpose, they wouldn't exist, obviously.Quote:
Originally Posted by abachler
That's mostly what I was referring to. Volatile is a tricky subject. I don't use them at all and it works fine. So the must have or not can be a tricky question already discussed to great lengths.Quote:
Originally Posted by Codeplug