Stopping multiple executions

[Clay Clear]

Henning,

i have never used a Mutex in a DLL. You may want to consider
doing so in the LIBMAIN function, and open or close the mutex
depending on the Reason that the LIBMAIN was called.

This is an idea, only, as I've never used them in DLL's.

Regards,


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Clay C. Clear

Clay Clear's Software
mailto:[email protected][email protected]</A>

[Henning Wallgren]

Semen,

Thanks for clearing it up.

------------------
Henning

[Semen Matusovski]

Henning --
You should close Mutex, when it's not necessary anymore.
In certain situation - exactly before program termination (in PbMain).

Meanwhile, like Edwin mentioned, OS closes the handle automatically when the process terminates.
So, to close or not to close is mostly a style of programming.
You can leave a file opened. Here is the same.

Personally I follow a logic - if I opened/created, I should close/destroy.



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E-MAIL: [email protected]

[Henning Wallgren]

Hi all

I've been using Clay/Semen's Mutex sample which I put into a DLL.
So far this has worked 100%. However, Clay, if I use the commented line
it does not.. With the multitude of ways suggested, can I consider
this a safe way?

FUNCTION ProgramRunning(byval program$) EXPORT AS LONG
FUNCTION = %FALSE
DIM szTemp AS ASCIIZ * %MAX_PATH
szTemp = program$
DIM hMutex AS LONG
hMutex = CreateMutex(BYVAL %NULL, 0, szTemp)
IF hMutex = %NULL THEN FUNCTION = %TRUE
IF GETLASTERROR = %ERROR_ALREADY_EXISTS THEN FUNCTION = %TRUE
'CloseHandle hMutex
END FUNCTION


------------------
Henning

I don't do this (it is quite lame ) but it seems one might use a "semaphore" file to control multiple executions and check for proper shutdown of the last instance of the app which was running.

#Dim All
#Register None
#Option Version4
 
Type SemaphoreType
  AppAlreadyRunning       As Long
  LastShutdownSuccessful  As Long
End Type
 
 
'  Put in Registry or cfg/ini file
$Hash = "0102030405060708090A0B0C0D0E0F101112131415161718191A"
$SemaPath = "SemaPhore\"
 
Declare Function AppRunning( HashName As String ) As Long
Declare Function ReHash( HashHex As String ) As String
Declare Sub CreateDirectoryTree( ByVal NewPath As String )
Declare Sub DoStuff()
Declare Sub UpdateSemaphore( ReHashName As String )
 
Global CurDrive$
 
Function PbMain
  Local lResult As Long
  CurDrive$ = Left$(CurDir$,3)
  'Create the Path for the SemaPhore file
  CreateDirectoryTree CurDrive$ & $SemaPath
 
  lResult = AppRunning(ReHash($Hash))
  If (lResult > 0& ) Then
    Beep
    Select Case lResult
      Case 1&
        StdOut "No can Do.  App Running..."
      Case 2&
        StdOut "No can Do.  Semaphore File already opened."
    End Select
    Exit Function
  End If
 
  DoStuff
  Call UpdateSemaphore( ReHash($Hash) )
End Function
 
 
Sub DoStuff
  WaitKey$
End Sub
 
 
Function AppRunning( ReHashName As String ) As Long
  Local DaError   As Long
  Local udtSema   As SemaphoreType
 
  ErrClear
  Open CurDrive$ & $SemaPath & ReHashName For Binary Access Read Write Lock Read Write As #1
  DaError = ErrClear
  If DaError > 0& Then
    StdOut "Error Opening Semaphore File:" & Str$(DaError)
    Function = 2&
  End If
  Get #1,, udtSema
 
  Select Case udtSema.AppAlreadyRunning
    Case 0&
      udtSema.AppAlreadyRunning = 1&
      udtSema.LastShutdownSuccessful = 0&
      Put #1,1, udtSema
      Function = 0&
 
    Case 1&
      If udtSema.LastShutdownSuccessful = 0& Then
        Function = 1&
      Else
        Function = 0&
      End If
  End Select
  Close 1
End Function
 
 
Sub UpdateSemaphore( ReHashName As String )
  Local DaError   As Long
  Local udtSema   As SemaphoreType
 
  udtSema.LastShutdownSuccessful = 1&
  udtSema.AppAlreadyRunning = 0&
  ErrClear
  Open CurDrive$ & $SemaPath & ReHashName For Binary Access Write Lock Read Write As #1
  DaError = ErrClear
  If DaError > 0& Then
    StdOut "Error Opening Semaphore File:" & Str$(DaError) & "!  Investigate and manually update file."
    Exit Sub
  End If
 
  Put #1,, udtSema
  Close 1
End Sub
 
 
Function ReHash( HashHex As String ) As String
  '  Do something real here with hash code...
  Rehash = "HashTest"
End Function
 
Sub CreateDirectoryTree( ByVal NewPath As String )
  Local s   As String
  Local Pth As String
  Local l   As Long
 
  If Right$(NewPath,1) = "\" Then
    NewPath = Left$(NewPath, Len(NewPath) -1 )
  End If
 
  l = 1
  Do
    s = Parse$( NewPath, "\", l )
    If Len(s) > 0& Then
      Pth = Pth & s & "\"
      MkDir Pth
      Incr l
    Else
      Exit Do
    End If
  Loop
End Sub

[This message has been edited by Ron Pierce (edited September 28, 2001).]

[Semen Matusovski]

I don't think that it's necessary to think about viruses.
Another question that "correct" app should activate first instance.
For this purpose SetProp could be much more useful.

Correct "activation" code is a separate thread.
Here I used "quick" (but not 100% correct) method, because wanted to show SetProp only.

   #Compile Exe
   #Dim All
   #Register None
   #Include "WIN32API.INC"

   %Sign1 = &H12345678&  ' Any unique
   %Sign2 = &H90123456&


   Function EnumWindowsProc(ByVal hWnd As Long, Param As Long Ptr) As Long
      If GetProp (hWnd, ByVal 1) = %Sign1 Then _
         If GetProp (hWnd, ByVal 2) = %Sign2 Then @Param = hWnd: Exit Function
      Function = 1
   End Function

   CallBack Function DlgProc
     Select Case CbMsg
     Case %WM_INITDIALOG
        SetProp CbHndl, ByVal 1, ByVal %Sign1
        SetProp CbHndl, ByVal 2, ByVal %Sign2
     End Select
   End Function

   Function PbMain
      Dim hDlg As Long, k As Long
      EnumWindows CodePtr(EnumWindowsProc), VarPtr(k)
      If k <> 0 Then ShowWindow k, %SW_RESTORE: SetForegroundWindow k: Exit Function ' dirty and incorrect method; simply for test
      Dialog New  %HWND_DESKTOP, "Started at " + Time$, 240, 120, 150, 60, %WS_CAPTION Or %WS_OVERLAPPEDWINDOW To hDlg
      Dialog Show Modal hDlg, Call DlgProc
   End Function

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E-MAIL: [email protected]

[Wayne Diamond]

Henning, well lets just say that youve developed a security program, and it uses a mutex to determine if it's already running. Just say its mutex name is "MyMutex" (remembering that mutexes are case sensitive ). A virus/trojan could find your security program (which could be as easy as one call to FindWindow) and then terminate it. Once it has terminated your program (which also naturally terminates all mutexes created by that process), it can then create the mutex "MyMutex". From that point on, you wouldn't be able to use your security program, because every time you tried to run it it would detect the mutex and assume that it's already running, even though it's actually the trojan/virus that is using the mutex - not another instance of your program.

So! I was just suggesting that if you are building a program that could be targetted by trojans/viruses such as security programs then it would be a wise idea not to use a fixed mutex name like "MyMutex". If your mutex is based on a unique checksum or mathematical algorithm then there's a very good chance that no trojan/virus author would bother going to such a length just to stop your program from running, but with plaintext fixed mutexes like "MyName" there's no effort, it's game set and match with one call to CreateMutex

For example, I dont know if this is still the case, but ZoneAlarm (the personal firewall) used a mutex called something like "ZAMutex"! Needless to say it didnt take long for some trojan authors to realise this.
Its not really something you need to worry about though if your program isn't likely to be the target of viruses/trojans, but just something to be aware of nonetheless!
I hope that makes a bit more sense

Also this applies not just to mutexes. If your security program uses (for example) FindWindow to determine if it is already running, then a trojan just has to create a window with the same title that your program looks for, pretty much the same as the mutex problem. A less efficient but more secure method would be to literally check the process list to see if your process is listed more than once

Best,
Wayne


[This message has been edited by Wayne Diamond (edited September 27, 2001).]

[Henning Wallgren]

Wayne,

Do you have any examples of how to do that (what you just said is
unfortunately greek to me..) ?


------------------
Henning

[Edwin Knoppert]

The good part is that it isn't required to destroy the mutex as suggested above.

This saves programming.


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http://www.hellobasic.com

[Wayne Diamond]

A note of caution if you use mutexes to determine if your prog is already alive - 3rd party programs (including trojans/viruses etc) can use your mutex if your program isn't running/using it, so your program can effectively be blocked and won't be able to run. This wouldn't apply to programs such as simple tools and utilities, but certainly would apply to any security-related programs! (I recall that ZoneAlarm's components each have a fixed mutex name, big no no!)
So rather than using a fixed mutex name, you may want to use a secure hash (MD5/SHA)
Best,
Wayne


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[Clay Clear]

Henning,

You're quite welcome.

You should note that, if you use my sample, you should also put
in your code, right before "EXIT FUNCTION" or "END FUNCTION"
the following:

CloseHandle hMutex

Sorry for forgetting to mention that.

Regards,


------------------
Clay C. Clear

Clay Clear's Software
mailto:[email protected][email protected]</A>

[Henning Wallgren]

Thanks Clay,

That was the easiest of all codes to implement.

I found a well of ways of doing it here and in POFFS (once I knew
what to look for) including a short samplecode from Semen who
always seems to provide a right to the point sample. Thank you.




------------------
Henning

[Clay Clear]

This is the code I use, which uses a Mutex:

DIM szTemp AS ASCIIZ*%MAX_PATH
szTemp = "myprogram.exe"
'
DIM hMutex AS LONG
'
hMutex = CreateMutex(BYVAL %NULL, 0, szTemp)
IF hMutex = %NULL THEN EXIT FUNCTION

IF GetLastError = %ERROR_ALREADY_EXISTS THEN EXIT FUNCTION

I believe Semen posted the original code.

Hope this helps!

Regards,


------------------
Clay C. Clear

Clay Clear's Software
mailto:[email protected][email protected]</A>

[This message has been edited by Clay Clear (edited September 26, 2001).]

[Henning Wallgren]

Thanks guys.

------------------
Henning

[Edwin Knoppert]

I have a mutex example too on my site IN the helpfile i believe..


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http://www.hellobasic.com

[Borje Hagsten]

lasse rantanen once posted a way. see http://www.powerbasic.com/support/pb...ad.php?t=17497


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[Sven Blumenstein]

Originally posted by Henning Wallgren:
Hi all

I was wondering how I can stop multiple executions of my program?

Search the Forum for "App Previnstance"


------------------
Sven Blumenstein
IT-Trainee at DECOMA Exterior Systems, Germany
E-Mail: mailto:[email protected][NOSPAM]cycos.net[email protected][NOSPAM]cycos.net</A>
Programming with: PB/DLL, MASM, VB, VC++, LCC, VBA, WML

[Henning Wallgren]

Hi all

I was wondering how I can stop multiple executions of my program?



------------------
Henning