separate thread to prevent progress bar from 'freezing' in c++ - c++

Question

I built a simplest progress bar which shows the progress of my png frame generation. Here is the process
BOOL myProc(HWND hwndParent, HINSTANCE hInst) {
RECT rcClient;
int cyVScroll;
HWND hwndPB;
DWORD cb;
GetClientRect(hwndParent, &rcClient);
cyVScroll = GetSystemMetrics(SM_CYVSCROLL);
hwndPB = CreateWindowEx(0, PROGRESS_CLASS, (LPTSTR) NULL,
WS_CHILD | WS_VISIBLE, rcClient.left,
rcClient.bottom - cyVScroll,
rcClient.right, cyVScroll,
hwndParent, (HMENU) 0, hInst, NULL);
int N = lastFrame;
SendMessage(hwndPB, PBM_SETRANGE, 0, MAKELPARAM(0, N));
SendMessage(hwndPB, PBM_SETSTEP, (WPARAM)1, 0);
for (int i = 0; i < N + 1; i++) {
int frame = create_pngInt(i);
SendMessage(hwndPB, PBM_STEPIT, 0, 0);
}
DestroyWindow(hwndPB);
DestroyWindow(hwndParent);
return TRUE;
}
I want my window to host just this progress bar. When the loop in myProc is done, the host window should be destroyed.
int WINAPI WinMain(HINSTANCE hInst, HINSTANCE PrevInst, LPSTR args, int ncmdshow) {
WNDCLASSW wc = { 0 };
wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hInstance = hInst;
wc.lpszClassName = L"GenPng";
wc.lpfnWndProc = WindowProcedure;
wc.hbrBackground = CreateSolidBrush(0x00171c00);
wc.hIcon = hIcon;
if (!RegisterClassW(&wc))
return -1;
hMainWindow = CreateWindowW(L"GenPng", L"Generating pngs", WS_VISIBLE | WS_OVERLAPPEDWINDOW,
200,
100, 300, 58, NULL, NULL, NULL, NULL);
std::thread q(myProc, hMainWindow, hInst);
MSG msg = { 0 };
while (GetMessage(&msg, NULL, NULL, NULL))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
However, the window hMainWindow is not destroyed (!) and the process myProc doesn't terminate by itself (after the loop in myProc is comlete).
It seems I don't understand something important.
I checked. If I don't create a separate thread but just run myProc in WinMain, the window hosting the progress bar destroyed after myProc returns. And this is precisely what I want. But the progress bar freezes after several seconds(. That is why I need a separate thread.
Following your remarks I modified the code like this:
int WINAPI WinMain(HINSTANCE hInst, HINSTANCE PrevInst, LPSTR args, int ncmdshow) {
RECT rect;
WNDCLASSW wc = { 0 };
wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hInstance = hInst;
wc.lpszClassName = L"GenPng";
wc.lpfnWndProc = WindowProcedure;
wc.hbrBackground = CreateSolidBrush(0x00171c00);
wc.hIcon = hIcon;
if (!RegisterClassW(&wc))
return -1;
hMainWindow = CreateWindowW(L"GenPng", L"Generating pngs", WS_VISIBLE | WS_OVERLAPPEDWINDOW,
200,
100, 300, 58, NULL, NULL, NULL, NULL);
SetWindowPos(hMainWindow, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE);
RECT rcClient;
int cyVScroll;
HWND hwndPB;
DWORD cb;
GetClientRect(hMainWindow, &rcClient);
cyVScroll = GetSystemMetrics(SM_CYVSCROLL);
hwndPB = CreateWindowEx(0, PROGRESS_CLASS, (LPTSTR)NULL,
WS_CHILD | WS_VISIBLE, rcClient.left,
rcClient.bottom - cyVScroll,
rcClient.right, cyVScroll,
hMainWindow, (HMENU)0, hInst, NULL);
int N = lastFrame;
SendMessage(hwndPB, PBM_SETRANGE, 0, MAKELPARAM(0, N));
SendMessage(hwndPB, PBM_SETSTEP, (WPARAM)1, 0);
std::thread q(myProc, hMainWindow, hInst, hwndPB);
MSG msg = { 0 };
while (GetMessage(&msg, hMainWindow, NULL, NULL))
{
if (msg.message == WM_QUIT) {
DestroyWindow(hMainWindow);
}
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return 0;
}
However, I know that I haven't handled WM_QUIT event properly, and the whole thing is not destroyed. Could you please, elaborate just a little bit more and if the rest of the code is ok?

Answer 1

The thread which calls CreateWindowEx needs to be the one executing the GetMessage loop.
It won't get destroyed, as there is nothing processing the events and messages for it, including the WM_DESTROY message.
Keep your window creation in your main thread (and that thread only!), and use only PostMessage / SendMessage to send update events and finally a destroy message to the window owned by the main thread.
Ultimately handle a WM_DESTROY to your main window with PostQuitMessage and your are done.
In full:
int WINAPI WinMain(HINSTANCE hInst, HINSTANCE PrevInst, LPSTR args, int ncmdshow) {
RECT rect;
WNDCLASSW wc = { 0 };
wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
wc.hInstance = hInst;
wc.lpszClassName = L"GenPng";
wc.lpfnWndProc = WindowProcedure;
wc.hbrBackground = CreateSolidBrush(0x00171c00);
wc.hIcon = hIcon;
if (!RegisterClassW(&wc))
return -1;
hMainWindow = CreateWindowW(
L"GenPng", L"Generating pngs", WS_VISIBLE | WS_OVERLAPPEDWINDOW,
200,
100, 300, 58, NULL, NULL, NULL, NULL
);
SetWindowPos(hMainWindow, HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE);
RECT rcClient;
int cyVScroll;
HWND hwndPB;
DWORD cb;
GetClientRect(hMainWindow, &rcClient);
cyVScroll = GetSystemMetrics(SM_CYVSCROLL);
hwndPB = CreateWindowEx(
0, PROGRESS_CLASS, (LPTSTR)NULL,
WS_CHILD | WS_VISIBLE, rcClient.left,
rcClient.bottom - cyVScroll,
rcClient.right, cyVScroll,
hMainWindow, (HMENU)0, hInst, NULL
);
int N = lastFrame;
SendMessage(hwndPB, PBM_SETRANGE, 0, MAKELPARAM(0, N));
SendMessage(hwndPB, PBM_SETSTEP, (WPARAM)1, 0);
std::thread q([hMainWindow, hInst, hwndPB, N]() {
for (int i = 0; i < N + 1; i++) {
SendMessage(hwndPB, PBM_STEPIT, 0, 0);
}
DestroyWindow(hMainWindow);
});
MSG msg = { 0 };
while (GetMessage(&msg, NULL, NULL, NULL))
{
if (msg.message == WM_DESTROY) {
PostQuitMessage(0);
}
TranslateMessage(&msg);
DispatchMessage(&msg);
}
q.join();
// Exit code from PostQuitMessage() is still in msg.param
return msg.param;
}