I have a Windows app written in C (using gcc/MinGW) that works pretty well except for a few UI problems. One, I simply cannot get the progress bar to update from a thread. In fact, I probably can't get ANY UI stuff to update.

Basically, I have a spawned thread that does some processing, and from that thread I attempt to update the progress bar in the main thread. I tried this by using PostMessage() to the main hwnd, but no luck even though I can do other things like open message boxes. However, it's unclear whether the message box is getting called within the thread or on the main thread.

Here's some code:

//in header/globally accessible
HWND wnd; //main application window
HWND progress_bar; //progress bar

typedef struct { //to pass to thread
    DWORD mainThreadId;
    HWND mainHwnd;
    char *filename;
} THREADSTUFF;


//callback function
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam){
    switch(msg){
        case WM_CREATE:{
            //create progress bar
            progress_bar = CreateWindowEx(
                0,
                PROGRESS_CLASS,
                (LPCTSTR)NULL,
                WS_CHILD | WS_VISIBLE,
                79,164,455,15,
                hwnd,
                (HMENU)20,
                NULL,
                NULL);
            break;
        }

        case WM_COMMAND:{
            if(LOWORD(wParam)==2){ //do some processing in a thread

                //struct of stuff I need to pass to thread
                THREADSTUFF *threadStuff;
                threadStuff = (THREADSTUFF*)malloc(sizeof(*threadStuff));
                threadStuff->mainThreadId = GetCurrentThreadId();
                threadStuff->mainHwnd = hwnd;
                threadStuff->filename = (void*)&filename;
                hThread1 = CreateThread(NULL,0,convertFile (LPVOID)threadStuff,0,NULL);

            }else if(LOWORD(wParam)==5){ //update progress bar

                MessageBox(hwnd,"I got a message!", "Message",  MB_OK | MB_ICONINFORMATION);
                PostMessage(progress_bar,PBM_STEPIT,0,CLR_DEFAULT);
            }
            break;
        }
    }
}

This all seems to work okay. The problem is in the thread:

DWORD WINAPI convertFile(LPVOID params){

    //get passed params, this works perfectly fine
    THREADSTUFF *tData = (THREADSTUFF*)params;

    MessageBox(tData->mainHwnd,tData->filename,"File name",MB_OK | MB_ICONINFORMATION); //yep

    PostThreadMessage(tData->mainThreadId,WM_COMMAND,5,0); //only shows message
    PostMessage(tData->mainHwnd,WM_COMMAND,5,0); //only shows message
}

When I say, "only shows message," that means the MessageBox() function in the callback works, but not the PostMessage() to update the position of the progress bar.

What am I missing?