Question

In one of my class i’m launching a thread using the following method:

HANDLE hThread;
unsigned threadID;
hThread = (HANDLE)_beginthreadex( NULL, 0, &myThread, NULL, 0, &threadID );

And from this thread I would like to call a method that has to be called from the main thread (the method is interacting with the UI) but I really don’t know how to do it since the main thread can’t wait until “myThread” notifies it.

I have seen a lot of

while(true){
  //wait something from myThread
}

But I can’t wait this way!

Any ideas?

Answer 1

Since your main thread is UI, you can send a message to it.

#define WM_USER_EXECUTE_MY_CODE (WM_USER + 1000)

Your UI message loop should process the message:

// API code
// LRESULT CALLBACK WndProc(HWND hwnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
// create message map yourself if you're using MFC

if (iMsg == WM_USER_EXECUTE_MY_CODE)
{
    // execute your code must run in main thread
}

And in your worker thread, send UI a message

// HWND hwnd = handle to main UI window
// if you need some parameters, send them through WPARAM or LPARAM
SendMessage(hwnd, WM_USER_EXECUTE_MY_CODE, 0, 0);