Msgbox doesn't display after PostQuitMessage

[Mike Doty]

2/24/09
This thread from 3 days ago is about preventing the user from closing a dialog with "X" or using ALT+F4
PostQuitMessage should never have been used.
Solutions are in post #11.
--------------------------------------------------------------------------------------------------



What is wrong with this code?
If MSGBOX is placed before PostQuitMessage it works.
If placed after PostQuitMessage the msgbox does not display and dialog can not be closed even if threads have finished.
Don't plan on using the MSGBOX, but curious.

Code to prevent user from closing dialog before all threads have finished.

CASE %WM_SYSCOMMAND
          IF THREADCOUNT > 1 THEN
              PostQuitMessage 0
              ? "Threads still active" + STR$(THREADCOUNT) 'doesn't display, program can't end
              FUNCTION =1
          END IF

[Michael Mattias]

One of two things is happening:

1. MSGBOX is MODAL, creating its own message loop, which executes asynchronously from the program's primary message loop.

WM_QUIT reaches and is processed by that primary message loop as soon as MSGBOX is started up, and the normal handling of WM_QUIT is to end the GUI thread. (Insufficient code shown).

I think you could get the messagebox to display by suspending the primary thread after the MSGBOX (SLEEP ought to do it); but that is going to be a timing thing, so it's not going to be terribly reliable in any event.

2. THREADCOUNT is not greater than one, in which case the default procedure will handle WM_SYSCOMMAND, so what happens is dependent on the notification code in wParam.

MCM

[Edwin Knoppert]

I did try to use Msgbox during a WM_DESTROY ever.
It may be Windows does not allow this box during a 'critical' message.

I don't know.

[Mike Doty]

Wrote a smaller test program, here.
It appears I got pretty lazy in not checking for a mouse click in SYS_COMMAND.
The dialog couldn't be moved or resized.
Wrote this improvement, but MSGBOX should still NOT go after PostQuitMessage.
'SYS_COMMAND thread
http://www.powerbasic.com/support/pb...=WM_SYSCOMMAND

#PBFORMS CREATED V1.51
#COMPILE EXE
#DIM ALL
'------------------------------------------------------------------------------
'   ** Includes **
'------------------------------------------------------------------------------
#PBFORMS BEGIN INCLUDES
#IF NOT %DEF(%WINAPI)
    #INCLUDE "WIN32API.INC"
#ENDIF
#PBFORMS END INCLUDES
'------------------------------------------------------------------------------
'------------------------------------------------------------------------------
'   ** Constants **
'------------------------------------------------------------------------------
#PBFORMS BEGIN CONSTANTS
%IDD_DIALOG1 = 101
#PBFORMS END CONSTANTS
'------------------------------------------------------------------------------
'------------------------------------------------------------------------------
'   ** Declarations **
'------------------------------------------------------------------------------
DECLARE CALLBACK FUNCTION ShowDIALOG1Proc()
DECLARE FUNCTION ShowDIALOG1(BYVAL hParent AS DWORD) AS LONG
#PBFORMS DECLARATIONS
'------------------------------------------------------------------------------
'------------------------------------------------------------------------------
'   ** Main Application Entry Point **
'------------------------------------------------------------------------------
FUNCTION PBMAIN()
    ShowDIALOG1 %HWND_DESKTOP
    ? "PBMAIN EXIT"
END FUNCTION
'------------------------------------------------------------------------------
'------------------------------------------------------------------------------
'   ** CallBacks **
'------------------------------------------------------------------------------
CALLBACK FUNCTION ShowDIALOG1Proc()
    LOCAL dw AS DWORD
    SELECT CASE AS LONG CBMSG
        CASE %WM_INITDIALOG
            ' Initialization handler
            THREAD CREATE t(CBHNDL) TO dw
            THREAD CLOSE dw TO dw
            SLEEP 250
 
        CASE %WM_NCACTIVATE
            STATIC hWndSaveFocus AS DWORD
            IF ISFALSE CBWPARAM THEN
                ' Save control focus
                hWndSaveFocus = GetFocus()
            ELSEIF hWndSaveFocus THEN
                ' Restore control focus
                SetFocus(hWndSaveFocus)
                hWndSaveFocus = 0
            END IF
        CASE %WM_COMMAND
            ' Process control notifications
            SELECT CASE AS LONG CBCTL
            END SELECT
 
        CASE %WM_SYSCOMMAND
            IF (CBWPARAM AND &HFFF0) = %SC_CLOSE THEN
               FUNCTION = 1
               IF THREADCOUNT > 1 THEN  'only end if no extra threads
                 MSGBOX "Can not end yet, thread count" + STR$(THREADCOUNT) 'ok
                 PostQuitMessage 0
                 'MSGBOX "THIS IS NOT OKAY
               ELSE
                 FUNCTION = 1
                 PostMessage CBHNDL, %WM_USER + 2048, 0, 0
                 EXIT FUNCTION
               END IF
            END IF
        CASE %WM_USER + 2048
            ? "2048"
            DIALOG END CBHNDL
        'CASE %WM_SYSCOMMAND
        '    IF (CB.WPARAM AND &HFFF0) = %SC_CLOSE THEN
        '      IF THREADCOUNT > 1 THEN   'Dialog can't be resized/moved
        '                                'until thread has finished
        '        PostQuitMessage 0
        '        ? "Thread is still running"
        '        FUNCTION = 0
        '      END IF
        '    END IF
    END SELECT
END FUNCTION
'------------------------------------------------------------------------------
'------------------------------------------------------------------------------
'   ** Dialogs **
'------------------------------------------------------------------------------
FUNCTION ShowDIALOG1(BYVAL hParent AS DWORD) AS LONG
    LOCAL lRslt AS LONG
#PBFORMS BEGIN DIALOG %IDD_DIALOG1->->
    LOCAL hDlg  AS DWORD
    DIALOG NEW hParent, "Dialog1", 325, 196, 204, 121, %WS_POPUP OR _
        %WS_BORDER OR %WS_DLGFRAME OR %WS_THICKFRAME OR %WS_CAPTION OR _
        %WS_SYSMENU OR %WS_CLIPSIBLINGS OR %WS_VISIBLE OR %DS_MODALFRAME OR _
        %DS_3DLOOK OR %DS_NOFAILCREATE OR %DS_SETFONT, %WS_EX_CONTROLPARENT _
        OR %WS_EX_LEFT OR %WS_EX_LTRREADING OR %WS_EX_RIGHTSCROLLBAR, TO _
        hDlg
#PBFORMS END DIALOG
    DIALOG SHOW MODAL hDlg, CALL ShowDIALOG1Proc TO lRslt
#PBFORMS BEGIN CLEANUP %IDD_DIALOG1
#PBFORMS END CLEANUP
    FUNCTION = lRslt
END FUNCTION
'------------------------------------------------------------------------------
THREAD FUNCTION t(BYVAL hDlg AS DWORD) AS DWORD
  LOCAL x AS LONG
  FOR x = 10 TO 1 STEP -1
      DIALOG SET TEXT hDlg, STR$(x) + " ThreadCount" + STR$(THREADCOUNT)
      SLEEP 1000
  NEXT
END FUNCTION

CASE %WM_SYSCOMMAND
    IF (CBWPARAM AND &HFFF0) = %SC_CLOSE THEN
      IF THREADCOUNT > 1 THEN  'prevent end if extra threads
        ? "Thread count still" + STR$(THREADCOUNT) 'ok before PostQuitMessage
        PostQuitMessage 0
        'Do not put any MSGBOX statements in here
        FUNCTION = 1
      END IF
    END IF

[Michael Mattias]

PostQuitMessage is 'conventionally' called on WM_DESTROY, not on WM_SYSCOMMAND (any).

Do that=end of problems.

[Mike Doty]

PostQuitMessage did not stop dialog from ending in my testing within %WM_DESTROY. I would like to see a working example. Thanks for trying.

Here is a solution and MSGBOX (if used) does not cause a problem.

 CASE %WM_SYSCOMMAND
     IF (CBWPARAM AND &HFFF0) = %SC_CLOSE THEN
       IF THREADCOUNT > 1 THEN FUNCTION = 1 'prevent dialog end
     END IF

Thanks to Bern Ertl (post #3)
http://www.powerbasic.com/support/pb...5WM_SYSCOMMAND

[Michael Mattias]

Here is a solution and MSGBOX (if used) does not cause a problem.

 CASE %WM_SYSCOMMAND
     IF (CBWPARAM AND &HFFF0) = %SC_CLOSE THEN

If you had said originally you were interested in the SC_CLOSE notification this would have been a lot simpler. Your posted code problem expresses interest in 'any' notification provided via WM_SYSCOMMAND.

But I think I said that: " ... so what happens is dependent on the notification code in wParam. "

As far as using WM_DESTROY, a current thread on this subject is at http://www.powerbasic.com/support/pb...ad.php?t=39941. I think the key statement there is "it *IS* too late..." . That may be of interest, too.

[Mike Doty]

Original posting title was confusing.
The code did show this:
Code to prevent user from closing dialog before all threads have finished.

Off subject, but I dislike postings that are titled "Need help".

To prevent a dialog from ending when using clicks X or if Alt+F4 is used
only requires FUNCTION=1 in %WM_SYSCOMMAND
My use of PostQuitMessage was entirely incorrect.

CASE %WM_SYSCOMMAND
     IF (CBWPARAM AND &HFFF0) = %SC_CLOSE THEN
       IF THREADCOUNT > 1 THEN FUNCTION = 1 'prevent dialog end
     END IF

[Michael Mattias]

Another way to do it is to disable the SC_CLOSE option on the system menu until you wish to permit that action. If the user can't click the "X" or "Close" he knows he ain't ending now.

(I'm pretty sure that handles Alt+F4, too).

I know there are examples here.

MCM

[Mike Doty]

Good suggestion. I'll post code for that later today.

RemoveMenu(GetSystemMenu(CBHNDL, %False), %SC_CLOSE, %MF_BYCOMMAND) 'removes X
It does not disable the Alt+F4.
Not sure how to force the "X" (caption) to be refreshed. Resizing the window refreshes.

[Mike Doty]

Works, but would think a windows handle would have been needed

This appears to work, but I would have thought the windows handle rather
than CBHNDL would have been necessary.

RemoveMenu(GetSystemMenu(CBHNDL, %False), %SC_CLOSE, %MF_BYCOMMAND)
DrawMenuBar CBHNDL

Before any thread is created the X is disabled (code above.)
When threads finish they see if they were the last thread and if so enable X.

IF THREADCOUNT = 2 THEN    'allow user to end, thread count about to be 1
    RemoveMenu(GetSystemMenu(ghDlg, %True), %SC_CLOSE, %MF_BYCOMMAND)
    DrawMenuBar ghDlg
END IF

This takes care of Alt+F4. Disabling "X" does not handle it.

CASE %WM_SYSCOMMAND
     IF (CBWPARAM AND &HFFF0) = %SC_CLOSE THEN
       IF THREADCOUNT > 1 THEN FUNCTION = 1 'prevent dialog end
     END IF