[RESOLVED] Prevent windows shutdown

I want my application to be always running. I have included password so that if someone tries to close the application, it will ask for password. Now I am trying to prevent windows from shutting down, restart or logging off while my application is running. Whenever it happens, my application will flash some message. I tried MsgHook component (MsgHoo32.OCX) from http://vb.mvps.org/tools/MsgHook/ to intercept windows message WM_QUERYENDSESSION

I have 2 problems.

1. In the WM_QUERYENDSESSION description it is mentioned that the application may return FALSE to cancel shutdown. How can I return a value while using MsgHook.

2. I used following code without returning any value. It works, but some other programs (mostly in system tray) are still unloaded. After that my program shows "Shutting Down" message & then shut down is cancelled.

Code:

Private Const WM_QUERYENDSESSION = &H11 Private Const ENDSESSION_LOGOFF As Long = &H80000000 Private Const WM_CANCELMODE = &H1F Private Sub Form_Load() Msghook1.HwndHook = Me.hWnd 'intercept messages for my window Msghook1.Message(WM_QUERYENDSESSION) = True 'enable event for WM_QUERYENDSESSION End Sub Private Sub Msghook1_Message(ByVal msg As Long, ByVal wp As Long, ByVal lp As Long, result As Long) If msg = WM_QUERYENDSESSION Then ' result = False MsgBox "Shutting Down" ' Else ' result = Msghook1.InvokeWindowProc(msg, wp, lp) End If End Sub Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer) Msghook1.Message(WM_QUERYENDSESSION) = False Msghook1.HwndHook = 0 'unhook any window End Sub

How can I prevent shutdown so that no program should be closed?
Thanks

Re: Prevent windows shutdown

You will need to test and this is at the form level but I think you can trap it this way:

Code:

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer) Select Case UnloadMode Case vbFormControlMenu MsgBox "The user chose the Close command (the ""X"") from the Control menu on the form." Case vbFormCode MsgBox "The Unload statement is invoked from code." Case vbAppWindows MsgBox "The current Microsoft Windows operating environment session is ending." Case vbAppTaskManager MsgBox "The Microsoft Windows Task Manager is closing the application." Case vbFormMDIForm MsgBox "An MDI child form is closing because the MDI form is closing." Case vbFormOwner MsgBox "A form is closing because its owner is closing." End Select End sub

focus on:

Case vbAppWindows
MsgBox "The current Microsoft Windows operating environment session is ending."
Case vbAppTaskManager
MsgBox "The Microsoft Windows Task Manager is closing the application."

Re: Prevent windows shutdown

" It works, but some other programs (mostly in system tray) are still unloaded. After that my program shows "Shutting Down" message & then shut down is cancelled." -- that's not surprising... they're probably getting closed down before your app is requested to close. your app may be stopping the shutdown process, but if other apps/services have already shut down... you can't really do a whole lot about that.

-tg

Re: Prevent windows shutdown

Quote:

Originally Posted by vbdev100

1. ... How can I return a value while using MsgHook.

You were correct in using the result [out] parameter.

Quote:

Originally Posted by vbdev100

2. I used following code without returning any value. It works, ...

That's because functions return False by default. However, the Else clause in your code shouldn't have been commented out. It prevents other messages you may be watching for from reaching the previous window procedure.

Quote:

Originally Posted by vbdev100

How can I prevent shutdown so that no program should be closed?

MSDN says:

Quote:

If any application returns zero, the session is not ended. The system stops sending WM_QUERYENDSESSION messages as soon as one application returns zero.

When an application returns TRUE for this message, it receives the WM_ENDSESSION message, regardless of how the other applications respond to the WM_QUERYENDSESSION message. Each application should return TRUE or FALSE immediately upon receiving this message, and defer any cleanup operations until it receives the WM_ENDSESSION message.

That means the OS sequentially sends the WM_QUERYENDSESSION to each application. If an application closes before another one postpones the shutdown, then there's not much that can be done about that. However, if your app starts early enough (and will be running throughout), then it'll be the first one that the OS sends the WM_QUERYENDSESSION message to. If your app returns FALSE, then you effectively prevented other apps from receiving WM_QUERYENDSESSION and thus closing.

If you're using VB5/6, you actually don't need the MsgHook component because the AddressOf operator available in those versions enable native subclassing. Also, VB already has the capability you're looking for, as TysonLPrice showed you. Here's code equivalent to yours:

Code:

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer) If UnloadMode = vbAppWindows Then Cancel = True End Sub

For Vista and later OSes, the ShutdownBlockReasonCreate function et al. is the proper way of telling the OS not to shutdown. BTW, users who are prevented from shutting down their computers are most likely going to turn it off at the switch. Happened to me once with a DVD-burner app. :mad:

Re: Prevent windows shutdown

Quote:

Originally Posted by vbdev100

Now I am trying to prevent windows from shutting down, restart or logging off while my application is running.

Why ?

Re: Prevent windows shutdown

Quote:

Originally Posted by Doogle

Why ?

Because, my application should monitor some machines continuously & it should not be closed by any means.

Re: Prevent windows shutdown

Then (IMHO) it should be running as a 'non-stoppable Service'. You shouldn't be preventing a machine from shutting down and your Service should respect a machine Shutdown request.

Re: Prevent windows shutdown

Quote:

Originally Posted by TysonLPrice

You will need to test and this is at the form level but I think you can trap it this way:

Code:

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer) Select Case UnloadMode Case vbFormControlMenu MsgBox "The user chose the Close command (the ""X"") from the Control menu on the form." Case vbFormCode MsgBox "The Unload statement is invoked from code." Case vbAppWindows MsgBox "The current Microsoft Windows operating environment session is ending." Case vbAppTaskManager MsgBox "The Microsoft Windows Task Manager is closing the application." Case vbFormMDIForm MsgBox "An MDI child form is closing because the MDI form is closing." Case vbFormOwner MsgBox "A form is closing because its owner is closing." End Select End sub

focus on:

Case vbAppWindows
MsgBox "The current Microsoft Windows operating environment session is ending."
Case vbAppTaskManager
MsgBox "The Microsoft Windows Task Manager is closing the application."

Thanks, vbAppWindows works perfectly. I added 'Cancel = True' & shutdown was prevented. But some programs were ended earlier.

Your solution also clicked me an idea of preventing to end my application from task manager. So I tried it but I get the program is not responding message. The shutdown can continue either automatically after some period or by pressing the end button. Anyway, this was not my requirement.

If windows sends the WM_QUERYENDSESSION message in some particular sequence/priority (may be some system windows like desktop gets it earlier), I can trap the message from there???

Re: Prevent windows shutdown

Bonnie West, thanks!

I commented out the Else clause in my code, because only the WM_QUERYENDSESSION message is enabled to trap in MsgHook. So even 'If' clause is also not necessary (I think) as I have enabled only one message.

Quote:

You were correct in using the result [out] parameter.

I am still not able to understand the return method. Is result = False alright?

Thanks.

Re: Prevent windows shutdown

Quote:

Originally Posted by vbdev100

Is result = False alright?

Yes.

Notice that the result parameter is declared implicitly As ByRef. That means the original variable's memory address was passed to that function so that you can directly manipulate its value.

Please refer to the MSDN doc Passing Arguments to Procedures for a more complete discussion.

Re: Prevent windows shutdown

Quote:

Originally Posted by vbdev100

If windows sends the WM_QUERYENDSESSION message in some particular sequence/priority (may be some system windows like desktop gets it earlier), I can trap the message from there???

According to my tests, the system sends that message in the order that programs were started. So, if you could ensure that your app starts before everything else, there's a good chance it will be able to block that message from reaching the others.

My tests seem to indicate that the explorer.exe process waits for all the processes' response before it decides what to do. If one app returns FALSE after the others exited, the explorer process remains alive.

I'm not sure if the WM_QUERYENDSESSION message can be trapped with Hooking...

Re: Prevent windows shutdown

Quote:

Originally Posted by Doogle

Then (IMHO) it should be running as a 'non-stoppable Service'. You shouldn't be preventing a machine from shutting down and your Service should respect a machine Shutdown request.

I agree with Doogle.
I'm curious how your program is going to prevent a user from just pulling the power-cord.....:rolleyes:

Re: Prevent windows shutdown

Thanks Bonnie West,

Now I understood the result parameter correctly.

For now, I am quitting the idea of hooking any window. As I don't know beforehand which window will be first to get the message. So either using the WM_QUERYENDSESSION message or deny in Form_QueryUnload event will be more or less the same thing. And yes, the WM_QUERYENDSESSION message can be trapped because I got the 'shutting down' message which was in Msghook1_Message event.

I used the following code to popup password screen to allow exit/shutdown. (Though some programs are closed, but mine NOT). I did not check for UnloadMode.

Code:

Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer) If PwdExit Then PwdType = Pwd.ProgExit frmPassword.Show vbModal, Me If Not FrmEnding Then Cancel = True Exit Sub End If End If Screen.MousePointer = vbHourglass tmrTime.Enabled = False tmrTimeOut.Enabled = False CloseAllRecords Unload frmSock RemoveIcon Me ' FrmEnding = True If Not qryShift Is Nothing Then qryShift.Close Set qryShift = Nothing Call CloseDB . . . .

Re: Prevent windows shutdown

Quote:

So, if you could ensure that your app starts before everything else,

do you know some way to do that?

Re: Prevent windows shutdown

this in a module

Code:

Option Explicit Public Declare Function SetWindowLong Lib "user32.dll" Alias "SetWindowLongA" ( _ ByVal hwnd As Long, _ ByVal nIndex As Long, _ ByVal dwNewLong As Long) As Long Public Declare Function CallWindowProc Lib "user32.dll" Alias "CallWindowProcA" ( _ ByVal lpPrevWndFunc As Long, _ ByVal hwnd As Long, _ ByVal Msg As Long, _ ByVal wParam As Long, _ ByVal lParam As Long) As Long Public Const WM_QUERYENDSESSION As Long = &H11 Public Const GWL_WNDPROC As Long = -4 Public oldProc As Long Public Function WindowProc(ByVal hwnd As Long, ByVal iMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long If iMsg = WM_QUERYENDSESSION Then WindowProc = 0 Else WindowProc = CallWindowProc(oldProc, hwnd, iMsg, wParam, lParam) End If End Function

with this in form of project should prevent windows from shutting down

Code:

Option Explicit Private Sub Form_Load() oldProc = SetWindowLong(Me.hwnd, GWL_WNDPROC, AddressOf WindowProc) End Sub Private Sub Form_Unload(Cancel As Integer) SetWindowLong Me.hwnd, GWL_WNDPROC, oldProc End Sub

Re: Prevent windows shutdown

Thanks, this small & clean code is really self-explanatory.

Re: Prevent windows shutdown

The WindowProc function can be simplified a bit:

Quote:

Originally Posted by Rattled_Cage

Code:

Public Function WindowProc(ByVal hwnd As Long, ByVal iMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long If iMsg <> WM_QUERYENDSESSION Then WindowProc = CallWindowProc(oldProc, hwnd, iMsg, wParam, lParam) End Function

Re: Prevent windows shutdown

Quote:

Originally Posted by westconn1

do you know some way to do that?

The Sysinternals' Autoruns for Windows should be quite helpful.

EDIT

Here are a couple more potentially useful links:

how to start program before user logon windows 7
Understand and Control Startup Apps with the System Configuration Utility

Re: Prevent windows shutdown

hmm .... I certianly would not want any program on my computer that prevented me from doing a normal shutdown or restart nor would I create such a thing as it would be very intrusive.

Basically such a program would prevent you from being able to install some software, updates or just restart when the system was unstable and would force the user to power off the computer or hit the reset button neither of which is a good idea.

Should sucha thing exist on one of my systems the first thing I would do is shut it down then boot to a different OS and delete the program and all hooks to it just like I would with any other virus or malicous software that is not auto removed by my virus scanner.

Re: Prevent windows shutdown

Quote:

I certianly would not want any program on my computer that prevented me from doing a normal shutdown or restart

i would be very keen to have something like this, to prevent automatic reboots by windows updates or other programs that think it is their god given right to control my computer when ever they like regardless of what data i may loose
i would of course prefer it written by me, with option to continue shutdown if i was the one initiating the shutdown

i will look at the link posted above to see if i can make my program the first to be loaded, so that no data will be lost from other programs

Re: Prevent windows shutdown

Hello,

This code does not work for Windows Vista, Windows 7 and Windows 8 ... Is there another valid code for these operating systems?

Thank you very much!

Quote:

Originally Posted by Rattled_Cage

this in a module

Code:

Option Explicit Public Declare Function SetWindowLong Lib "user32.dll" Alias "SetWindowLongA" ( _ ByVal hwnd As Long, _ ByVal nIndex As Long, _ ByVal dwNewLong As Long) As Long Public Declare Function CallWindowProc Lib "user32.dll" Alias "CallWindowProcA" ( _ ByVal lpPrevWndFunc As Long, _ ByVal hwnd As Long, _ ByVal Msg As Long, _ ByVal wParam As Long, _ ByVal lParam As Long) As Long Public Const WM_QUERYENDSESSION As Long = &H11 Public Const GWL_WNDPROC As Long = -4 Public oldProc As Long Public Function WindowProc(ByVal hwnd As Long, ByVal iMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long If iMsg = WM_QUERYENDSESSION Then WindowProc = 0 Else WindowProc = CallWindowProc(oldProc, hwnd, iMsg, wParam, lParam) End If End Function

with this in form of project should prevent windows from shutting down

Code:

Option Explicit Private Sub Form_Load() oldProc = SetWindowLong(Me.hwnd, GWL_WNDPROC, AddressOf WindowProc) End Sub Private Sub Form_Unload(Cancel As Integer) SetWindowLong Me.hwnd, GWL_WNDPROC, oldProc End Sub

Re: Prevent windows shutdown

Quote:

Originally Posted by Korku

This code does not work for Windows Vista, Windows 7 and Windows 8 ... Is there another valid code for these operating systems?

In case you've overlooked post # 4 above, see the last paragraph.

Re: Prevent windows shutdown

Quote:

Originally Posted by westconn1

i would be very keen to have something like this, to prevent automatic reboots by windows updates or other programs that think it is their god given right to control my computer when ever they like regardless of what data i may loose
i would of course prefer it written by me, with option to continue shutdown if i was the one initiating the shutdown

i will look at the link posted above to see if i can make my program the first to be loaded, so that no data will be lost from other programs

Isn't there settings on windows to do this already, to ask a user if he wants to install updates, or automatically install updates.
This would prevent windows from doing automatic reboots, but maybe not other programs.

To be honest I never had a program restart my computer for me, it always asked me if I wanted to reboot later or reboot now.
I guess it could happen and if your working on a project (VB,EXCEL,PHOTO SHOP,AUTOCAD) and it shuts down windows and you forgot to save for an hour or more then it would ruin the whole project!
In this case a program to prevent from rebooting would actually be fantastic! :)

Re: Prevent windows shutdown

Quote:

Originally Posted by Bonnie West

In case you've overlooked post # 4 above, see the last paragraph.

Ok, do you have a code example of how to run the function ShutdownBlockReasonCreate? Thank you!

Re: Prevent windows shutdown

Quote:

Originally Posted by Korku

Ok, do you have a code example of how to run the function ShutdownBlockReasonCreate? Thank you!

Code:

Option Explicit 'Reason string should be <= MAX_STR_BLOCKREASON, else it is truncated Private Const SHUTDOWN_BLOCK_REASON As String = "Unable to shutdown for some reason." Private Const MAX_STR_BLOCKREASON As Long = 256 Private Declare Function ShutdownBlockReasonCreate Lib "user32.dll" (ByVal hWnd As Long, ByVal pwszReason As Long) As Long Private Declare Function ShutdownBlockReasonDestroy Lib "user32.dll" (ByVal hWnd As Long) As Long Private Sub Form_Load() Dim RetVal As Long RetVal = ShutdownBlockReasonCreate(hWnd, StrPtr(SHUTDOWN_BLOCK_REASON)) Debug.Assert RetVal 'If code stops here, ShutdownBlockReasonCreate failed End Sub Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer) If UnloadMode = vbAppWindows Then Cancel = True 'Still need to do this End Sub Private Sub Form_Unload(Cancel As Integer) Dim RetVal As Long RetVal = ShutdownBlockReasonDestroy(hWnd) Debug.Assert RetVal 'If code stops here, ShutdownBlockReasonDestroy failed End Sub

Application Shutdown Changes in Windows Vista is highly recommended reading! :thumb:

Re: [RESOLVED] Prevent windows shutdown

Quote:

Isn't there settings on windows to do this already, to ask a user if he wants to install updates, or automatically install updates.
This would prevent windows from doing automatic reboots, but maybe not other programs.

if the user does not click later, it will wait a short while then reboot, when running unattended this can be a problem, also i have in the past clicked the default (restart now) when the dialog pops up, as focus had changed from what i was previously doing, some registry changes did help, but still have issues on W7 when automatic updates are on

Re: Prevent windows shutdown

Works fine! Thank you very much!

But it's not what I want. What I want is that when you try to shut down the computer with the application open, display a message something like "You must close the application before turning off the computer."

Also this sample code closes the programs that are in the background.

I'm trying to make a remote connection application for a tablet with Windows 8, I wanted to avoid placing in sleep mode or turned off when the application is open.

Quote:

Originally Posted by Bonnie West

Code:

Option Explicit 'Reason string should be <= MAX_STR_BLOCKREASON, else it is truncated Private Const SHUTDOWN_BLOCK_REASON As String = "Unable to shutdown for some reason." Private Const MAX_STR_BLOCKREASON As Long = 256 Private Declare Function ShutdownBlockReasonCreate Lib "user32.dll" (ByVal hWnd As Long, ByVal pwszReason As Long) As Long Private Declare Function ShutdownBlockReasonDestroy Lib "user32.dll" (ByVal hWnd As Long) As Long Private Sub Form_Load() Dim RetVal As Long RetVal = ShutdownBlockReasonCreate(hWnd, StrPtr(SHUTDOWN_BLOCK_REASON)) Debug.Assert RetVal 'If code stops here, ShutdownBlockReasonCreate failed End Sub Private Sub Form_QueryUnload(Cancel As Integer, UnloadMode As Integer) If UnloadMode = vbAppWindows Then Cancel = True 'Still need to do this End Sub Private Sub Form_Unload(Cancel As Integer) Dim RetVal As Long RetVal = ShutdownBlockReasonDestroy(hWnd) Debug.Assert RetVal 'If code stops here, ShutdownBlockReasonDestroy failed End Sub

Application Shutdown Changes in Windows Vista is highly recommended reading! :thumb:

Re: Prevent windows shutdown

Quote:

Originally Posted by Korku

But it's not what I want. What I want is that ...

You should've made that clear right from the start. :cool:

Quote:

Originally Posted by Korku

... when you try to shut down the computer with the application open, display a message something like "You must close the application before turning off the computer."

ShutdownBlockReasonCreate already does that. Isn't that what you want? The SHUTDOWN_BLOCK_REASON constant in the example code in post #25 above can be modified as desired.

Quote:

Originally Posted by Korku

Also this sample code closes the programs that are in the background.

Well, it could be because of the reason mentioned in posts #3 & #4. It might also be because those programs have no visible top-level window. As discussed in the Application Shutdown Changes in Windows Vista:

Quote:

Originally Posted by MSDN

Windows Vista will also not allow console applications or applications that have no visible top-level windows to block shutdown. In most cases, such applications are less important to users at shutdown than applications that do have visible top-level windows. If an application without a visible top-level window blocks shutdown by vetoing WM_QUERYENDSESSION, or takes over 5 seconds to respond to WM_QUERYENDSESSION or WM_ENDSESSION, Windows will automatically terminate it.

Quote:

Originally Posted by Korku

I'm trying to make a remote connection application for a tablet with Windows 8, I wanted to avoid placing in sleep mode or turned off when the application is open.

As pointed out several times already, you shouldn't prevent the user from shutting down the computer. Even Microsoft agrees:

Quote:

Originally Posted by Application Shutdown Changes in Windows Vista

Applications should not block shutdown

If you take only one thing away from reading this topic, it should be this one. You will be presenting the best experience to your users if your application does not block shutdown. When users initiate shutdown, in the vast majority of cases, they have a strong desire to see shutdown succeed; they may be in a hurry to leave the office for the weekend, for example. Applications should respect this desire by not blocking shutdown if at all possible.

In many cases, applications that block shutdown can be redesigned so that they no longer need to do so. For example, applications with unsaved data at shutdown can be designed to automatically save their data and restore it when the user next starts the application, instead of blocking shutdown to ask the user what to do. Microsoft Office 2007 will do this in certain scenarios.

In other cases, there is usually a sensible default action that applications should automatically perform, instead of blocking shutdown to ask the user what to do. In many cases, this is true even if the default action could be slightly destructive. Read more...