Handle message from another thread in Win32 windows - c++

Question

I created a window with Win32s, I wish it could handle incoming messages from another thread in addition to typical windows messages.
I'm using this piece of code:
while (dataAvailable || GetMessage(&msg, nullptr, 0, 0))
{
// if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))
if (dataAvailable == true)
{
cout << "My thread message/signal!" << endl;
dataAvailable = false;
}
else
{
//Windows message
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
the "DataAvailable" is an atomic bool that I set when I would like pass a my own message to win32 app/windows.
This don't work well.
It is possible to do this?

Answer 1

I suggest you to use standard messages. Register your own new message and use PostMessage from another thread to your main window thread.
I base my example code on standard windows sample code: https://github.com/microsoft/Windows-classic-samples/blob/main/Samples/Win7Samples/begin/LearnWin32/HelloWorld/cpp/main.cpp
In this code I add a standard std::thread :
// ...
auto th1 = std::thread([=] {
const UINT WM_EX_SOME_SPECIALINTERNALMESSAGE = ::RegisterWindowMessage(L"SomeSpecialInternalMessage");
for (int n = 0; n < 10; ++n) {
PostMessage(hwnd, WM_EX_SOME_SPECIALINTERNALMESSAGE, 0, 0);
Sleep(1000);
}
});
// Run the message loop.
MSG msg = { };
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
th1.join();
As you see in this code, WM_EX_SOME_SPECIALINTERNALMESSAGE is a custom windows message. Its posted every second to you main window proc: WindowProc. To receive it modify WindowProc:
LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
const UINT WM_EX_SOME_SPECIALINTERNALMESSAGE = ::RegisterWindowMessage(L"SomeSpecialInternalMessage");
if(uMsg == WM_EX_SOME_SPECIALINTERNALMESSAGE) {
OutputDebugStringW(L"WM_EX_SOME_SPECIALINTERNALMESSAGE\n");
}
// ...