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**Michael Mattias** · 5 Mar 2000, 03:35 AM

You want to share data among multiple Windows of the same class in the same thread of the same process? (Is this Win-32?)

The data are aleady shared. If you need data unique to each Window, that's where you use the WindowExtra field. Any size limitation on the number of extra bytes is easily overcome: just save a (four-byte) pointer to a block you allocate on receipt of the WM_CREATE message.

MCM

**LRantanen** · 5 Mar 2000, 05:38 AM

Here is one sample how it can be done - allowing only one instance to run. The idea has been around some time - make a search in the net. Works under Win9x/NT 4 (at least).

Lasse Rantanen
[email protected]

Code:

#COMPILE EXE
#INCLUDE "WIN32API.INC"
 
%IDCLOSE                = 10000
 
%PAGE_READONLY          = &H002 ' Defines for these constants are missing from PB/DLL include files.
 
GLOBAL hFile AS LONG
 
DECLARE CALLBACK FUNCTION DlgProc
 
'==============================================================================
FUNCTION PBMAIN() AS LONG
 
    LOCAL hDlg      AS LONG
    LOCAL szMapName AS ASCIIZ*16
 
    szMapName = "MyAppsName" ' Make sure this is unique
 
    hFile = CreateFileMapping(&HFFFFFFFF, _
                              BYVAL %NULL, _
                              %PAGE_READONLY , _
                              0, _
                              10, _
                              szMapName)
 
    IF (hFile > 0) AND (GetLastError() = %ERROR_ALREADY_EXISTS) THEN
        MSGBOX "Only one instance allowed!", _
                %MB_OK OR %MB_ICONSTOP, _
                szMapName
        UnmapViewOfFile hFile
        EXIT FUNCTION
    END IF
 
    DIALOG NEW  %HWND_DESKTOP, "Only Allowed Instance", _
                240, 120, 150, 60, _
                %WS_CAPTION + %WS_SYSMENU, TO hDlg
 
    CONTROL ADD BUTTON, hDlg, %IDCLOSE, "Close", _
                        35, 40, 80, 14, _
                        %WS_TABSTOP
 
    DIALOG SHOW MODAL hDlg, CALL DlgProc
 
END FUNCTION
 
'==============================================================================
CALLBACK FUNCTION DlgProc
 
    SELECT CASE CBMSG
 
        CASE %WM_COMMAND
 
            SELECT CASE CBWPARAM
 
                CASE %IDCLOSE
 
                    IF hFile>0 THEN UnmapViewOfFile hFile
 
                    DIALOG END CBHNDL
 
             END SELECT
    END SELECT
END FUNCTION

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[This message has been edited by LRantanen (edited March 05, 2000).]

**LRantanen** · 5 Mar 2000, 05:42 AM

Oops - forgot the closing [/code] tag and also noticed that I'm not talking exactly the same thing as E B Knoppert. However, this is also using shared memory and allowing only one instance to run - so maybe this qualify as a branch in this thread.

Lasse Rantanen
[email protected]

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**Eric Pearson** · 5 Mar 2000, 05:49 AM

Lasse --

> Oops - forgot the closing [/code] tag

You can always go back and edit a post that contains an error... just click the little "pencil and paper" icon to the right of the post date/time.

It's a little tricky sometimes... If the post already contains {code} tags you'll find that you have to remove the html tags (in angle brackets) and re-type the code and /code tags (in square brackets). That's a bug in the UBBS software.

-- Eric

------------------
Perfect Sync: Perfect Sync Development Tools
Email: mailto:[email protected][email protected]</A>

**LRantanen** · 5 Mar 2000, 06:19 AM

Thanks Eric,

went and did that.

Lasse Rantanen
[email protected]

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**E B Knoppert** · 5 Mar 2000, 10:40 AM

I was thinking about two things in one procedure.

Creating a global(!) class is noticable from another instance.
AND, it handles data, why shouldn't i take that opportunity?

Sure, a dozen diff. methods for this, Mutexes whatever.
just another tip..

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**LRantanen** · 5 Mar 2000, 06:19 PM

Sorry E B, at the first reading I misunderstood you. Just after hitting that Submit Reply button I realized I was talking about different thing.

BTW, what do you mean with a global class? A class registered with CS_GLOBALCLASS style? A class usable by every process? A couple of quotes - first one from a MSDN technical article "Window Classes in Win32" by Kyle Marsh.

16-BIT versions of Windows such as Windows 3.1 gave real meaning to application global classes. A DLL or application could register an application global class that any other DLL or application on the system could use. Thus, an application global class was a global class registered by an application instead of the system.

Application global classes are quite different in Win32. An application global class is a class that is available to all parts of a process.

MS Platform SDK defines

An application global class is a window class registered by an executable or dynamic-link library (.dll) that is available to all other modules in the process.

Then documentation describes how under NT you can write a DLL and register it under a certain registry key. Then every process loads that DLL and can use the application global class defined in it. As far as I understand this works only under NT.

IMHO, using this technique to detect previous instance will work only under NT and will require usage of a DLL and sounds somewhat complicated for this purpose.

Back to my posting. I realize there are other ways to prevent multiple instances and that what I supplied was just another tip. However, I haven't seen any supplied in these forums so after reading your message I thought to post one, because I thought that was what you were after. If I unintentionally offended you, I apologize.

Lasse Rantanen
[email protected]

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[This message has been edited by LRantanen (edited March 05, 2000).]

**E B Knoppert** · 6 Mar 2000, 12:40 AM

Lasse,
This was written before your last reply;

First, i think your solution is much better.
Didn't know that it was that easy, never used it before.
I was planning to test this soon to increase filereading speed.
(Lot's of seeks, ANYONE A SPEEDY SUGGESTION?)

But, we both have a problem.

If the app crashes, we are stuck with a 'flag' for prev. instance.

In win2000, the class remains, even while the DLL/EXE is closed.

Filemapping; (MSDN)

To fully close a file-mapping object,
an application must unmap all mapped views of the
file-mapping object by calling UnmapViewOfFile,
and close the file-mapping object handle by calling CloseHandle.
The order in which these functions are called does not matter.
The call to UnmapViewOfFile is necessary because mapped views
of a file-mapping object maintain internal open handles to the object,
and a file-mapping object will not close until all open handles to it are closed.

Note To guard against an access violation,
use structured exception handling to protect any code that
writes to or reads from a memory mapped view. For more information,
see Reading and Writing.

Let's forget the global class stuff, it wasn't the best idea.
(Therefore i posted it here..)

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**LRantanen** · 6 Mar 2000, 02:33 AM

E B,
that is a problem when mapping files into memory. You should carefully release/close all handles. In case of crash you are more or less out of luck, AFAIK. You have to try to catch as many errors as you can and close all handles opened so far.

Glad there is someone else struggling with this matter

Lasse Rantanen
[email protected]

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**Fred Oxenby** · 6 Mar 2000, 03:27 AM

(Edited by Administrator)

Have you thought about this little silly *******?
Easy to implement, no sideeffects(?).
Your first lines of code in the application will give you
a chance to detect another instance of the program.

The RegisterWindowMessage function is typically used to
register messages for communicating between two cooperating
applications.

If two different applications register the same message string,
the applications return the same message value. The message
remains registered until the session ends.

<font face="Courier New, Courier" size="3"><pre>
IsRunning& = RegisterWindowMessage("SPID_SLAV")
If SendMessage(%HWND_BROADCAST,IsRunning&,0&,0&)<> 0 then
Quit
End if
</pre></font>
I have not tried it but woud like opinions.
Like: Will there be a timout if no-one in the other end?

------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se

**Semen Matusovski** · 6 Mar 2000, 04:04 AM

I like to do
Open "Log" For Binary Lock Read Write
If, when a program starts, you are not able to open a file - means there is another instance

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**LRantanen** · 6 Mar 2000, 04:29 AM

Fred,

isn't following what happens:

RegisterWindowMessage -> a new message is registered
SendMessage(%HWND_BROADCAST,...) -> Window under construction responds to that message, so actually even the first instance does not start.

At least following behaves so

Code:

FUNCTION PBMAIN() AS LONG
 
    LOCAL hDlg      AS LONG
 
    IsRunning& = RegisterWindowMessage("SPLID_SLAV")
    IF SendMessage(%HWND_BROADCAST,IsRunning&,0&,0&)<> 0 THEN
        MSGBOX "Only one instance allowed!"
        EXIT FUNCTION
    END IF
 
    DIALOG NEW  %HWND_DESKTOP, "Only Allowed Instance", _
                240, 120, 150, 60, _
                %WS_CAPTION + %WS_SYSMENU, TO hDlg
 
    DIALOG SHOW MODAL hDlg, CALL DlgProc
    
END FUNCTION

I am not so familiar w/ DDT so if I am doing something wrong above, let me know.

Lasse Rantanen
[email protected]

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[This message has been edited by LRantanen (edited March 06, 2000).]

**Fred Oxenby** · 6 Mar 2000, 06:25 AM

It was a sloppy suggestion:
First: The returnvalue from IsRunning-test should not be
False or True. It should be some predefined value.
Second: It seems that DDT-engine always return "1"
whatever Returnvalue you assign.
Third: The methode works. Run one instance in the debugger and set breakpoint in DlgProc.
Then start a second instance and you will see that the broadcast
is handled. Unfortunatly not in DDT-engine
You have no "window" under creation, and your Msg-loop has to
be running to respond to this message

Code:

Your testprog modified
#Compile Exe
#Include "Win32Api.inc"
Global IsRunning&

CallBack Function DlgProc
 If CbMsg = IsRunning& Then
  Function = 5&:Exit Function
 End If
End Function

Function PbMain() As Long

    Local hDlg      As Long

    IsRunning& = RegisterWindowMessage("SPLID_SLAV")
    rc&= SendMessage(%HWND_BROADCAST,IsRunning&,0&,0&)
    #Debug Print Format$(rc&)
    If rc& = 5 Then
        MsgBox "Only one instance allowed!"
        Exit Function
    End If

    Dialog New  %HWND_DESKTOP, "First Instance", _
                240, 120, 150, 60, _
                %WS_CAPTION + %WS_SYSMENU, To hDlg

    Dialog Show Modal hDlg, Call DlgProc

End Function

------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se

[This message has been edited by Fred Oxenby (edited March 06, 2000).]

**Semen Matusovski** · 6 Mar 2000, 08:09 AM

RegisterWindowMessage really works, but it's seems to me that it's necessary to write something like this

Code:

#Compile Exe
#Include "Win32Api.inc"
Global IsRunning&

CallBack Function DlgProc
 Select Case CbMsg
    Case %WM_INITDIALOG
       SendMessage %HWND_BROADCAST, IsRunning&, 0&, 0&
    Case IsRunning&
       PostMessage CbHndl, %WM_USER + 999, 0, 0
    Case %WM_USER + 999
       Dialog End CbHndl
       MsgBox "Only one instance is allowed"
 End Select
End Function

Function PbMain() As Long
    Local hDlg      As Long
    IsRunning& = RegisterWindowMessage("SPLID_SLAV")
    Dialog New  %HWND_DESKTOP, "First Instance", _
                240, 120, 150, 60, _
                %WS_CAPTION + %WS_SYSMENU, To hDlg
    Dialog Show Modal hDlg, Call DlgProc
End Function

------------------

**jcfuller** · 6 Mar 2000, 08:39 AM

RE: RegisterWindowMessage

Correct me if I'm wrong but the message registered is valid until
the Windows session ends. I don't know if this will cause any problems on
systems that are seldom shut down but you should be aware of it.
Seems it would be more of an issue on a development systems??

James

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[This message has been edited by jcfuller (edited March 06, 2000).]

**Fred Oxenby** · 6 Mar 2000, 09:53 AM

James, the idea is to have someone answering your broadcast.
But it turns out that returnvalue ALWAYS is "1" whether it
is someone handling the message or not.
My assumption it was only the DDT-engine doing this was also
wrong.
The idea was to send this broadcast before you create any
windows, and it fell flat to the ground....
It will work, but you have to create a window,start the message-
loop, register TWO windowmessages (a send and a reply-message)
It will work nicely to communicate beetween two applications
but doesnot seem to qualify as an easy way to detect previous
instances.

------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se

**E B Knoppert** · 7 Mar 2000, 12:37 AM

For prev. inst. i do have some VB code to walk through the processes, this might be the best solution..

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Tip: Prev. inst.and shared mem.

Tip: Prev. inst.and shared mem.

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