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Communication between threads... Intercepting thread message


TA -- siemens@inet.uni-c.dk
Wednesday, December 18, 1996

Environment: VC++ 4.0, Windows95

Problem statement:
I want to post a message to a thread of my own derived CWinThread class in
order to tell it to self-terminate.
Although the thread is a CWinThread-derived one, it does not own a window,
and thus I use ::PostThreadMessage() to communicate with it. I use
CWinThread because it is able to process messages which is needed for the
CSocket objects, that it owns. I could, of course, create a class derived
from CCommandTarget but that is not the issue here.

I post a WM_COMMAND type message along with an ID but it won't work! The
message arrives perfectly at the thread's PreTranslateMessage() ( it is not
included in the sample below, but I have testet for it), but never reaches
the handler for which it is destined. The only way that
I see a solution to this problem is to use the PreTranslateMessage()
function, but I feel that this is an incorrect behaviour in MFC. Is there
an alternative to it? 

My code looks like this:

// ServerThread.h : header file
//
#ifndef __SERVERTHREAD_H__
#define __SERVERTHREAD_H__

#include "listensocket.h"

#define ID_KILL_SERVER_THREAD 100 // Command ID
////////////////////////////////////////////////////////////////////////////
/
// CSvrThread thread

class CServerThread : public CWinThread
{
	DECLARE_DYNCREATE(CServerThread)
protected:
	CServerThread();           // protected constructor used by dynamic
creation
	
	

// Attributes
public:
	CListenSocket* m_pListenSocket;
	int	m_nPort;

// Operations
public:

// Overrides
	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CServerThread)
	public:
	virtual BOOL InitInstance();
	virtual int ExitInstance();
//}}AFX_VIRTUAL

// Implementation
public:
	CServerThread(int nPort);

public:
	virtual ~CServerThread();

	// Generated message map functions
	//{{AFX_MSG(CServerThread)
		afx_msg void OnKillServerThread();
	//}}AFX_MSG

	DECLARE_MESSAGE_MAP()
};

////////////////////////////////////////////////////////////////////////////
/
#endif

// ServerThread.cpp : implementation file
//

#include "listensocket.h"
#include "stdafx.h"
#include "Control.h"
#include "ServerThread.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

////////////////////////////////////////////////////////////////////////////
/
// CServerThread

IMPLEMENT_DYNCREATE(CServerThread, CWinThread)

CServerThread::CServerThread()
{
}


CServerThread::CServerThread(int nPort) : m_nPort(nPort)
{
}


CServerThread::~CServerThread()
{
}


BOOL CServerThread::InitInstance()
{
	// Try to establish a server socket (listen socket)
	m_pListenSocket=NULL;
	try
	{
		m_pListenSocket = new CListenSocket;
	}
	catch (CMemoryException* e)
	{
		e->Delete();
		return FALSE;
	}

	if( m_pListenSocket->Create(m_nPort) ) 
	{
		if ( m_pListenSocket->Listen(1) )
			return TRUE;				
	}
	return FALSE;
}


int CServerThread::ExitInstance()
{
	if(m_pListenSocket) delete m_pListenSocket;
	return CWinThread::ExitInstance();
}


BEGIN_MESSAGE_MAP(CServerThread, CWinThread)
	//{{AFX_MSG_MAP(CServerThread)
		ON_COMMAND(ID_KILL_SERVER_THREAD,OnKillServerThread)
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

////////////////////////////////////////////////////////////////////////////
/
// CServerThread message handlers

afx_msg void CServerThread::OnKillServerThread()
{
	AfxEndThread(1);
}

// end of file ServerThread.cpp

As you probably can see, I've implemented the message as a WM_COMMAND
message; I perform the following to try to end the thread:
::PostThreadMessage(m_pSvrThreadID,WM_COMMAND,ID_KILL_SERVER_THREAD;NULL);
and then a ::WaitForSingleObject on the thread to allow time for it to
terminate.


Thanks for your time,

Mike Thomas Jakobsen
Siemens@inet.uni-c.dk
Siemens A/S
Borupvang 3
DK-2750 Ballerup
+45 4477 4477

Richard Braley -- braley@sky.net
Thursday, December 19, 1996

[Mini-digest: 4 responses]

Use the PostThreadMessage method of CWinThread to post a message to your =
thread and the ON_THREAD_MESSAGE macro to map the call to the =
appropriate message handler within your thread.
I have used this and it works fine.
Rick

----------
From: 	Siemens, TA[SMTP:siemens@inet.uni-c.dk]
Sent: 	Wednesday, December 18, 1996 10:13 AM
To: 	mfc-l
Subject: 	Communication between threads... Intercepting thread messages

Environment: VC++ 4.0, Windows95

Problem statement:
I want to post a message to a thread of my own derived CWinThread class =
in
order to tell it to self-terminate.
Although the thread is a CWinThread-derived one, it does not own a =
window,
and thus I use ::PostThreadMessage() to communicate with it. I use
CWinThread because it is able to process messages which is needed for =
the
CSocket objects, that it owns. I could, of course, create a class =
derived
from CCommandTarget but that is not the issue here.

I post a WM_COMMAND type message along with an ID but it won't work! The
message arrives perfectly at the thread's PreTranslateMessage() ( it is =
not
included in the sample below, but I have testet for it), but never =
reaches
the handler for which it is destined. The only way that
I see a solution to this problem is to use the PreTranslateMessage()
function, but I feel that this is an incorrect behaviour in MFC. Is =
there
an alternative to it?=20

My code looks like this:

// ServerThread.h : header file
//
#ifndef __SERVERTHREAD_H__
#define __SERVERTHREAD_H__

#include "listensocket.h"

#define ID_KILL_SERVER_THREAD 100 // Command ID
/////////////////////////////////////////////////////////////////////////=
///
/
// CSvrThread thread

class CServerThread : public CWinThread
{
	DECLARE_DYNCREATE(CServerThread)
protected:
	CServerThread();           // protected constructor used by dynamic
creation
=09
=09

// Attributes
public:
	CListenSocket* m_pListenSocket;
	int	m_nPort;

// Operations
public:

// Overrides
	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CServerThread)
	public:
	virtual BOOL InitInstance();
	virtual int ExitInstance();
//}}AFX_VIRTUAL

// Implementation
public:
	CServerThread(int nPort);

public:
	virtual ~CServerThread();

	// Generated message map functions
	//{{AFX_MSG(CServerThread)
		afx_msg void OnKillServerThread();
	//}}AFX_MSG

	DECLARE_MESSAGE_MAP()
};

/////////////////////////////////////////////////////////////////////////=
///
/
#endif

// ServerThread.cpp : implementation file
//

#include "listensocket.h"
#include "stdafx.h"
#include "Control.h"
#include "ServerThread.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] =3D __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////=
///
/
// CServerThread

IMPLEMENT_DYNCREATE(CServerThread, CWinThread)

CServerThread::CServerThread()
{
}

CServerThread::CServerThread(int nPort) : m_nPort(nPort)
{
}

CServerThread::~CServerThread()
{
}

BOOL CServerThread::InitInstance()
{
	// Try to establish a server socket (listen socket)
	m_pListenSocket=3DNULL;
	try
	{
		m_pListenSocket =3D new CListenSocket;
	}
	catch (CMemoryException* e)
	{
		e->Delete();
		return FALSE;
	}

	if( m_pListenSocket->Create(m_nPort) )=20
	{
		if ( m_pListenSocket->Listen(1) )
			return TRUE;			=09
	}
	return FALSE;
}

int CServerThread::ExitInstance()
{
	if(m_pListenSocket) delete m_pListenSocket;
	return CWinThread::ExitInstance();
}

BEGIN_MESSAGE_MAP(CServerThread, CWinThread)
	//{{AFX_MSG_MAP(CServerThread)
		ON_COMMAND(ID_KILL_SERVER_THREAD,OnKillServerThread)
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////=
///
/
// CServerThread message handlers

afx_msg void CServerThread::OnKillServerThread()
{
	AfxEndThread(1);
}

// end of file ServerThread.cpp

As you probably can see, I've implemented the message as a WM_COMMAND
message; I perform the following to try to end the thread:
::PostThreadMessage(m_pSvrThreadID,WM_COMMAND,ID_KILL_SERVER_THREAD;NULL)=
;
and then a ::WaitForSingleObject on the thread to allow time for it to
terminate.

Thanks for your time,

Mike Thomas Jakobsen
Siemens@inet.uni-c.dk
Siemens A/S
Borupvang 3
DK-2750 Ballerup
+45 4477 4477
-----From: Tim Robinson 

At 17:13 12/18/96 +0100, you wrote:
>Environment: VC++ 4.0, Windows95
>
>Problem statement:
>I want to post a message to a thread of my own derived CWinThread class in
>order to tell it to self-terminate.
>Although the thread is a CWinThread-derived one, it does not own a window,
>and thus I use ::PostThreadMessage() to communicate with it. I use
>CWinThread because it is able to process messages which is needed for the
>CSocket objects, that it owns. I could, of course, create a class derived
>from CCommandTarget but that is not the issue here.

Mike,

This is my first time around on dealing with threads like yours, but I
needed the same thing, so I'll pass on what I've got.  However, I'm
suspecting it won't work for 4.0.  An associate tried the following with 4.1
and it didn't work.  He had to upgrade to 4.2.

Anyway, use PostThreadMessage with a unique message (as you assume) and the
message handler is like the following:

  ON_THREAD_MESSAGE( WM_DIE, OnDie )

And the code is:

void CMyThread::OnDie( WPARAM, LPARAM )
  {
  PostQuitMessage(0);
  }

At least, that part worked for me.  You might need more.  Pretty simple once
I figured it out.

| Tim Robinson, Esquire          | Liberty  means responsibility. |
| timtroyr@ionet.net             | That is why most men dread it. |
| http://www.ionet.net/~timtroyr |            George Bernard Shaw |

-----From: "Dana M. Epp" 

I had a similar occassion to wonder about this myself. And like yourself, I
noticed it did enter PreTranslateMessage. I found out however that VC++ 4.0
and 4.1's message cracking doesn't deal with THREADED messages the same way
you would expect from other messages.. however your idealisms would work
fine. It seems that in 4.2 however, Microsoft added the ability to crack the
message with ON_THREAD_MESSAGE, which doesn't really help you with your 4.0
situation. However the PreTranslateMessage in this case is acceptable.
Taking from Mike B.'s authorship .. I derived my own 4.x thread solutions as
follows:

BOOL CDerivedThread::PreTranslateMessage(MSG* pMsg) 
{
	if( pMsg->hwnd == NULL ){
		if( pMsg->message == YOURMESSAGE ) 
                     OnYourMessage( pMsg->wParam, pMsg->lParam );
		return TRUE;
	}
	return CWinThread::PreTranslateMessage(pMsg);
}

Works fine, and until you move to 4.2, seems to be the best course for
dealing with threaded messages.

At 05:13 PM 12/18/96 +0100, you wrote:
>Environment: VC++ 4.0, Windows95
>
>Problem statement:
>I want to post a message to a thread of my own derived CWinThread class in
>order to tell it to self-terminate.
>Although the thread is a CWinThread-derived one, it does not own a window,
>and thus I use ::PostThreadMessage() to communicate with it. I use
>CWinThread because it is able to process messages which is needed for the
>CSocket objects, that it owns. I could, of course, create a class derived
>from CCommandTarget but that is not the issue here.
>
>I post a WM_COMMAND type message along with an ID but it won't work! The
>message arrives perfectly at the thread's PreTranslateMessage() ( it is not
>included in the sample below, but I have testet for it), but never reaches
>the handler for which it is destined. The only way that
>I see a solution to this problem is to use the PreTranslateMessage()
>function, but I feel that this is an incorrect behaviour in MFC. Is there
>an alternative to it? 
>
PC'ing you,                     
Dana M. Epp          
eppdm@uniserve.com
http://bedrock.cyberhq.com/dana

     "How can one work with the technology of today, using yesterdays
      software and methods, and still be on the leading edge tomorrow?
      Why settle for less... I won't! "

-----From: Chris.Byrneham@ubs.com

     Its a known problem with 4.0

     Go to www.microsoft.com/kb

     Search for Q142415

     Chris

Noel Burton-Krahn -- noel@harleystreet.com
Friday, December 20, 1996

[Mini-digest: 3 responses]

I have found that the PostThreadMessage() call in Win32 is almost 
completely useless.  If the thread expecting to receive a message ever 
creates a window, in all likelihood, the thread messages will be dequeued 
by the window and discarded before the thread's main message pump.  The 
problem lies in DispatchMessage() which simply discards messages with  a 
NULL hWnd.

In your application, you say that you do not create a window, so you think 
you would  be safe from this problem.  However, I believe that the windows 
socket implementation creates a hidden window for its own message passing. 
 I bet that is where your thread messages are going.

After many hours of frustration I have eschewed PostThreadMessage() from my 
vocabulary.  If I need  to pass messages to a thread, I create a hidden 
window.

---Noel

----------
From:  Siemens, TA[SMTP:siemens@inet.uni-c.dk]
Sent:  Wednesday, December 18, 1996 8:14 AM
To:  mfc-l
Subject:  Communication between threads... Intercepting thread messages

Environment: VC++ 4.0, Windows95

Problem statement:
I want to post a message to a thread of my own derived CWinThread class in
order to tell it to self-terminate.
Although the thread is a CWinThread-derived one, it does not own a window,
and thus I use ::PostThreadMessage() to communicate with it. I use
CWinThread because it is able to process messages which is needed for the
CSocket objects, that it owns. I could, of course, create a class derived
from CCommandTarget but that is not the issue here.

I post a WM_COMMAND type message along with an ID but it won't work! The
message arrives perfectly at the thread's PreTranslateMessage() ( it is not
included in the sample below, but I have testet for it), but never reaches
the handler for which it is destined. The only way that
I see a solution to this problem is to use the PreTranslateMessage()
function, but I feel that this is an incorrect behaviour in MFC. Is there
an alternative to it?

My code looks like this:

// ServerThread.h : header file
//
#ifndef __SERVERTHREAD_H__
#define __SERVERTHREAD_H__

#include "listensocket.h"

#define ID_KILL_SERVER_THREAD 100 // Command ID
////////////////////////////////////////////////////////////////////////  
////
/
// CSvrThread thread

class CServerThread : public CWinThread
{
	DECLARE_DYNCREATE(CServerThread)
protected:
	CServerThread();           // protected constructor used by dynamic
creation

// Attributes
public:
	CListenSocket* m_pListenSocket;
	int	m_nPort;

// Operations
public:

// Overrides
	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CServerThread)
	public:
	virtual BOOL InitInstance();
	virtual int ExitInstance();
//}}AFX_VIRTUAL

// Implementation
public:
	CServerThread(int nPort);

public:
	virtual ~CServerThread();

	// Generated message map functions
	//{{AFX_MSG(CServerThread)
		afx_msg void OnKillServerThread();
	//}}AFX_MSG

	DECLARE_MESSAGE_MAP()
};

////////////////////////////////////////////////////////////////////////  
////
/
#endif

// ServerThread.cpp : implementation file
//

#include "listensocket.h"
#include "stdafx.h"
#include "Control.h"
#include "ServerThread.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif

////////////////////////////////////////////////////////////////////////  
////
/
// CServerThread

IMPLEMENT_DYNCREATE(CServerThread, CWinThread)

CServerThread::CServerThread()
{
}

CServerThread::CServerThread(int nPort) : m_nPort(nPort)
{
}

CServerThread::~CServerThread()
{
}

BOOL CServerThread::InitInstance()
{
	// Try to establish a server socket (listen socket)
	m_pListenSocket=NULL;
	try
	{
		m_pListenSocket = new CListenSocket;
	}
	catch (CMemoryException* e)
	{
		e->Delete();
		return FALSE;
	}

	if( m_pListenSocket->Create(m_nPort) )
	{
		if ( m_pListenSocket->Listen(1) )
			return TRUE;				
	}
	return FALSE;
}

int CServerThread::ExitInstance()
{
	if(m_pListenSocket) delete m_pListenSocket;
	return CWinThread::ExitInstance();
}

BEGIN_MESSAGE_MAP(CServerThread, CWinThread)
	//{{AFX_MSG_MAP(CServerThread)
		ON_COMMAND(ID_KILL_SERVER_THREAD,OnKillServerThread)
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

////////////////////////////////////////////////////////////////////////  
////
/
// CServerThread message handlers

afx_msg void CServerThread::OnKillServerThread()
{
	AfxEndThread(1);
}

// end of file ServerThread.cpp

As you probably can see, I've implemented the message as a WM_COMMAND
message; I perform the following to try to end the thread:
::PostThreadMessage(m_pSvrThreadID,WM_COMMAND,ID_KILL_SERVER_THREAD;NULL);
and then a ::WaitForSingleObject on the thread to allow time for it to
terminate.

Thanks for your time,

Mike Thomas Jakobsen
Siemens@inet.uni-c.dk
Siemens A/S
Borupvang 3
DK-2750 Ballerup
+45 4477 4477

-----From: "Kenneth A. Argo" 

There is a tech note on thread messages.  Basically thread messages will =
not be able to use the default message routing available to MFC.   There =
is a procedure on making it work in the tech note.  If I remember =
correctly it has to do with an overload of OnPretranslateMessage() and =
looking at the HWND parameter of the MSG structure which will be NULL =
for a thread message (the cause of the problem ).

Ken

----------
From:  Siemens, TA[SMTP:siemens@inet.uni-c.dk]
Sent:  Wednesday, December 18, 1996 11:14 AM
To:  mfc-l
Subject:  Communication between threads... Intercepting thread messages

Environment: VC++ 4.0, Windows95

Problem statement:
I want to post a message to a thread of my own derived CWinThread class =
in
order to tell it to self-terminate.
Although the thread is a CWinThread-derived one, it does not own a =
window,
and thus I use ::PostThreadMessage() to communicate with it. I use
CWinThread because it is able to process messages which is needed for =
the
CSocket objects, that it owns. I could, of course, create a class =
derived
from CCommandTarget but that is not the issue here.

I post a WM_COMMAND type message along with an ID but it won't work! The
message arrives perfectly at the thread's PreTranslateMessage() ( it is =
not
included in the sample below, but I have testet for it), but never =
reaches
the handler for which it is destined. The only way that
I see a solution to this problem is to use the PreTranslateMessage()
function, but I feel that this is an incorrect behaviour in MFC. Is =
there
an alternative to it?=20

My code looks like this:

// ServerThread.h : header file
//
#ifndef __SERVERTHREAD_H__
#define __SERVERTHREAD_H__

#include "listensocket.h"

#define ID_KILL_SERVER_THREAD 100 // Command ID
/////////////////////////////////////////////////////////////////////////=
///
/
// CSvrThread thread

class CServerThread : public CWinThread
{
	DECLARE_DYNCREATE(CServerThread)
protected:
	CServerThread();           // protected constructor used by dynamic
creation
=09
=09

// Attributes
public:
	CListenSocket* m_pListenSocket;
	int	m_nPort;

// Operations
public:

// Overrides
	// ClassWizard generated virtual function overrides
	//{{AFX_VIRTUAL(CServerThread)
	public:
	virtual BOOL InitInstance();
	virtual int ExitInstance();
//}}AFX_VIRTUAL

// Implementation
public:
	CServerThread(int nPort);

public:
	virtual ~CServerThread();

	// Generated message map functions
	//{{AFX_MSG(CServerThread)
		afx_msg void OnKillServerThread();
	//}}AFX_MSG

	DECLARE_MESSAGE_MAP()
};

/////////////////////////////////////////////////////////////////////////=
///
/
#endif

// ServerThread.cpp : implementation file
//

#include "listensocket.h"
#include "stdafx.h"
#include "Control.h"
#include "ServerThread.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] =3D __FILE__;
#endif

/////////////////////////////////////////////////////////////////////////=
///
/
// CServerThread

IMPLEMENT_DYNCREATE(CServerThread, CWinThread)

CServerThread::CServerThread()
{
}

CServerThread::CServerThread(int nPort) : m_nPort(nPort)
{
}

CServerThread::~CServerThread()
{
}

BOOL CServerThread::InitInstance()
{
	// Try to establish a server socket (listen socket)
	m_pListenSocket=3DNULL;
	try
	{
		m_pListenSocket =3D new CListenSocket;
	}
	catch (CMemoryException* e)
	{
		e->Delete();
		return FALSE;
	}

	if( m_pListenSocket->Create(m_nPort) )=20
	{
		if ( m_pListenSocket->Listen(1) )
			return TRUE;			=09
	}
	return FALSE;
}

int CServerThread::ExitInstance()
{
	if(m_pListenSocket) delete m_pListenSocket;
	return CWinThread::ExitInstance();
}

BEGIN_MESSAGE_MAP(CServerThread, CWinThread)
	//{{AFX_MSG_MAP(CServerThread)
		ON_COMMAND(ID_KILL_SERVER_THREAD,OnKillServerThread)
	//}}AFX_MSG_MAP
END_MESSAGE_MAP()

/////////////////////////////////////////////////////////////////////////=
///
/
// CServerThread message handlers

afx_msg void CServerThread::OnKillServerThread()
{
	AfxEndThread(1);
}

// end of file ServerThread.cpp

As you probably can see, I've implemented the message as a WM_COMMAND
message; I perform the following to try to end the thread:
::PostThreadMessage(m_pSvrThreadID,WM_COMMAND,ID_KILL_SERVER_THREAD;NULL)=
;
and then a ::WaitForSingleObject on the thread to allow time for it to
terminate.

Thanks for your time,

Mike Thomas Jakobsen
Siemens@inet.uni-c.dk
Siemens A/S
Borupvang 3
DK-2750 Ballerup
+45 4477 4477

-----From: Mike Blaszczak 

At 20:22 12/19/96 -0600, Richard Braley wrote:

>Use the PostThreadMessage method of CWinThread to post a message to your 
>thread and the ON_THREAD_MESSAGE macro to map the call to the 
>appropriate message handler within your thread.

The original poster said that he was using VC++ 4.0, and therefore
MFC 4.0. MFC 4.0 doesn't have these features. They appeared in MFC 4.2.

.B ekiM
http://www.nwlink.com/~mikeblas/
I'm afraid I've become some sort of speed freak.
These words are my own. I do not speak on behalf of Microsoft.

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