Sending windows message from worker thread

GC104

Hello, I am currently getting to grips with MFC, VC++, VS2010 and threading. In particular I am trying to start a thread from a CMainFrame object, then post a windows message from the thread back to he CMainFrame object such that a messagebox can be displayed indicating the progress of the thread. In this example the uses starts the thread from a drop-down menu item (CreateWorkerThread function is called) the thread code executes and sends a single windows message towards the end of the thread. The problem I have is that CMainFrame doesn't seem to respond to the message unless the function that starts the thread uses a ::WaitForSingleObject() call. Why do I need to effectively pause the execution of the function creating the thread? Mayby naively, I assumed the following actions: -User selects Menu item -CreateWorkerThread() is called -Thread executes in parallel with the remains of CreateWorkerThread() -Worker thread generates a windows message (using ::PostMessage()) -By now CreateWorkerThread() would have completed. -CMainFrame Message map processes Worker Thread' message 'WM_THREAD1MSG' -Messagebox created and presented to user.

void CMainFrame::CreateWorkerThread(void)
// Created 25FEB2011
{

HWND hWnd = GetSafeHwnd();
if (hWnd == NULL)
{
	TRACE0("Window pointer is invalid!");
}


hWnd = GetSafeHwnd();	//hWnd has been made a 'public' member

pThread1 = AfxBeginThread(mcProc, static\_cast<LPVOID>(&hWnd), THREAD\_PRIORITY\_NORMAL, 0, CREATE\_SUSPENDED);	
pThread1 ->ResumeThread(); 

DWORD ThreadExitCodeValue = 0;
LPDWORD pDWord = NULL;
pDWord = &ThreadExitCodeValue;

//Need a handle for the thread:
HANDLE pThreadHandle = pThread1->m\_hThread;


::WaitForSingleObject(pThreadHandle,INFINITE); //stops this 'thread' until worker thread exits.

}

BEGIN_MESSAGE_MAP(CMainFrame, CFrameWndEx)
ON_WM_CREATE()

ON\_MESSAGE(WM\_THREAD1MSG, Respond2ThreadMsg)  //#define WM\_THREAD1MSG WM\_APP + 0x10 <- this line included in stdafx.h

ON\_COMMAND(ID\_VIEW\_CUSTOMIZE, &CMainFrame::OnViewCustomize)
ON\_REGISTERED\_MESSAGE(AFX\_WM\_CREATETOOLBAR, &CMainFrame::OnToolbarCreateNew)
ON\_COMMAND\_RANGE(ID\_VIEW\_APPLOOK\_WIN\_2000, ID\_VIEW\_APPLOOK\_WINDOWS\_7, &CMainFrame::OnApplicationLook)
ON\_UPDATE\_COMMAND\_UI\_RANGE(ID\_VIEW\_APPLOOK\_WIN\_2000, ID\_VIEW\_APPLOOK\_WINDOWS\_7, &CMainFrame::OnUpdateApplicationLook)

ON\_COMMAND(ID\_GCCODEDVMT\_TESTCOMMAND, TestCommand)		//GC added 23FEB2011
ON\_COMMAND(ID\_GCCODEDVMT\_CREATEWORKERTHREAD, C

CPallini

You're passing the address of a temporary variable to the thread: when CreateWorkerThread exits, hWnd goes out of scope. BTW: There is really no need to pass a pointer to the HWND, just pass the HWND value. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

GC104

Many thanks for feedback :) Since posting this message I realised that I have been using the WINAPI PostMessage() function call rather than the MFC wrapper CWnd::PostMessage(). Which is the preferred method? regards Geoff

prasad_som

You already got answer in earlier post. If you want to pass pointer to handle, use address of m_hHandle member variable, which is handle of CMainFrame. No need to call GetSafeHwnd.

prasad_som

CWnd::PostMessage internally calls win32 ::PostMessage. I'll use CWnd::PostMessage, if I've CWnd object(no need to wrap window handle, specially to use this version), and ::PostMessage, if I've window handle.

CPallini

GC104 wrote:

I have been using the WINAPI PostMessage() function call rather than the MFC wrapper CWnd::PostMessage()

You have to use the Windows API function. Worker threads aren't CWnd. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

CPallini

prasad_som wrote:

I'll use CWnd::PostMessage, if I've CWnd object(no need to wrap window handle, specially to use this version), and ::PostMessage, if I've window handle.

So you'll use both at the same time when you have a CWnd object... :rolleyes: Pardon the silly humour...

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]