[RESOLVED] getting windows of other threads

[Feoggou]

hi!

I have a dialogbased application, and I created another thread. the problem I have is that I cannot use the window (created by the main thread) in the second thread.

a call like this:

theApp.m_pMainWnd->SetWindowTextW(L"something");

in the second thread, causes the program to stop responding - I cannot use it anymore.

Can you please help me?

[Feoggou]

shouldn't my second thread have full access to the main thread? (like, to access freely its CWnd* -s, or HWND -s)

I tried sending WM_SETTEXT from this thread to another application, and it worked. But when I tried to send to my own application, to the window belonging to the main thread, the program stops responding, and, in Debug mode, I cannot step any more.

can anynody please tell me what the problem is and how I can solve it?

[hoxsiew]

How are you creating your thread? You should pass the HWND of the main UI window to the thread as it's thread parameter (or part of a structure passed in the thread parameter) then use SendMessage or PostMessage to interact with the main UI window.

[Feoggou]

initially it looked like this:

hSendThread = CreateThread(0, 0, (LPTHREAD_START_ROUTINE)SendThreadProc, this, 0, 0);

but now I've changed it into this:

hSendThread = CreateThread(0, 0, (LPTHREAD_START_ROUTINE)SendThreadProc, this->m_hWnd, 0, 0);

and still, the same things happens: it stops responding.

the definition of SendThreadProc:

DWORD SendThreadProc(HWND hWnd)
{
	WCHAR the_string[] = L"message";
	SendMessage(hWnd, WM_SETTEXT, 0, (LPARAM)the_string);
        // code here. at the above line it stops responding
}

the part of the code in which I create the thread:

void CMyProgramDlg::OnSend()
{
	SetDlgItemTextW(IDC_ST_SEND, L"Not Sending");

	//create the thread for sending the data
	hSendThread = CreateThread(0, 0, (LPTHREAD_START_ROUTINE)SendThreadProc, this->m_hWnd, 0, 0);
	
	//while sending, we disable the "Send" and the "Browse" buttons
	GetDlgItem(IDOK)->EnableWindow(0);
	GetDlgItem(IDC_BUTTON_BROWSE)->EnableWindow(0);

	WaitForSingleObject(hSendThread, INFINITE);
	CloseHandle(hSendThread);
        //code here
}

[hoxsiew]

At the end of you OnSend routine, you are calling WaitForSingleObject() on your thread routine so your parent thread is going to be blocked for the entirety of your threads existance, which is going to be a long time because SendMessage blocks until the parent hWnd processes the message, but it can't because it is waiting for the thread to end. In short, you have a deadlock.

[Feoggou]

yeah, you're right.

I solved the problem now. thanks.