Ensuring only one instance of a program – how?

[Erik Christensen]

Is there a simple method by which a program can ensure that there at any time is only one instance of another program running? Thanks in advance.

Best regards,

Erik

[Michael Mattias]

Multiple examples here.

Search 'mutex' and/or 'instance' in message subject.

[Guest]

?

Eric,

Is there a simple method by which a program can ensure that there at any time is only one instance of another program running?

Do you want to ensure, there is only one instance of your own program
running at a given time, or there is only one instance of a third
party program running at a given time.

What do you mean by ensure?
- just look to make sure (count instances)
- do something to make sure (kill a second (third and so on ..) instance)


Ensuring your own program runs only in a single instance is very easy.
You need some kind of a global flag (a file, a .ini file, a memory mapped
file, a mutex, a registry entry, ...). When your program starts, it must
check, if this flag is set. If so - it must abort (because there is already
another instance running), if not - it must set this flag by itself to prevent
other instances from running. When exiting don´t forget to reset this flag
again.


Hope this helps


guenther

[Erik Christensen]

I want to do something to make sure that only one instance of my own program exists at any time (i.e. kill a second (third and so on ..) instance).

I think the technique you describe Guenther is fine. I will try this. Thank you.

[Mel Bishop]

Check my MP3 player at:

http://www.powerbasic.com/support/pbforums/showthread.php?t=25095

and look for the Is_Already_Running function

[Erik Christensen]

Thanks.

I found a similar function in this thread:

http://www.powerbasic.com/support/pbforums/showthread.php?t=25148

This prevents more than one instance, which is fine.

If for some reason there are already more instances of a program, is it then possible to delete (by another program) the superfluous ones?

[Erik Christensen]

I just found this link:

http://www.powerbasic.com/support/pbforums/showthread.php?t=24019

I think this will answer my question.

[John Petty]

Eric
Just a reminder this is not as simple as it sounds if you are in a situation with multiple name spaces such as when running with Terminal Services or Citrix or even with XP or Vista with fast user switching as unless exceptionally careful many of the normally checked objects will only be visible in a single namespace.
Some discussion here http://www.powerbasic.com/support/pb...ad.php?t=37884
John

[Erik Christensen]

I managed to produce this code based on previous contributions in the PowerBasic Forum. Thanks a lot.

http://www.powerbasic.com/support/pbforums/showthread.php?p=303356

[Michael Mattias]

>I managed to produce this code ...

Kind of the 'long way,' isn't it?

$MUTEX_NAME = "whatever" 

FUNCTION WinMain(...) 

  SzMutex = $MUTEX_NAME 
  hMutex =  OpenMutex (....szMutex  no_ownership_needed) 
  IF ISTRUE Mutex THEN 
      'program already running , return error code and exit
      CloseHandle hMutex
      FUNCTION = 1 
      EXIT FUNCTION
  ELSE
     hMutex = CreateMutex (..) 
     ' next program instance will be able to open the mutex forcing it to exit
  END IF

  ' here there is a debate... you can CloseHandle (hMutex), or you can let 
  ' windows do it for you when your process completely ends. 
  '

END FUNCTION

[Gösta H. Lovgren-2]

Erik, here's some simpler code. I got most of it from the Forums a long time ago and don't remember who should get credit.

        Case %WM_INITDIALOG '<- for processing that needs to occur when the program loads 
            'Check to see if program already running
               Local hmutex&, smutex$ 'just used for testing program existence
            smutex$ = " Checkbook"   'Program name 
            hmutex& = CreateMutex(ByVal %Null, 0, ByVal StrPtr(smutex$))'check if running
            If hmutex& <> %Null Then 'Program probably already running
               If GetLastError() = %error_already_exists Then 'Constant defined in WinAPI
                  MsgBox SmuTex$ & " is already running", %Top, Using$("Error code #",Err)
                 Dialog Post CbHndl, %Dialog_End, 0, 0 'Tell program not to run
                                                       'Can't end it in %WM_InitDialog
                                                       'Tell it to end in %WM_Command
                 Exit Function 
              End If
            End If
            'Continue Any initializing code here

[Fred Buffington]

Here's what I use that is probably in one of the links provided in earlier posts

    CASE %WM_INITDIALOG
        gWhatApp = lTitle$ ' title to find 
        EnumWindows CODEPTR(EnumWindowsProc), 0
       IF gAppCount>1 THEN
         MSGBOX "Warning: "+FORMAT$(gAppCount) & " occurrence(s) of Client Writeup running"
       END IF

[Russ Srole]

Stick this in your WinMain function

    Local PrgName As Asciiz * 255
    Local hInstanceMutex&
    PrgName = "My_Program_Name" ' Important
    hInstanceMutex = CreateMutex(ByVal %Null, 0, PrgName)
    If hInstanceMutex = 0 Then Exit Function ' Error in Mutex
    If GetLastError = %ERROR_ALREADY_EXISTS Then
        MsgBox  "This old Program is already running"
        Exit Function
    End If

[Erik Christensen]

Many Thanks. The mutex method is fine, but if for some reason there are already more instances of a program, the method provided in the code may be better.
The routines by Graham McPhee can deal with all processes in the computer.

I actually used his routines for another code which lists all processes in the computer.

http://www.powerbasic.com/support/pbforums/showthread.php?p=303395

It may come as a surprise to you to see how many there are.

Best regards

Erik

[Michael Mattias]

>but if for some reason there are already more instances of a program

???

There can't be. You prevented this from happening.

???

You can't create program code on the assumption you have made an error. Kind of self-defeating, no?

[Erik Christensen]

I am talking about other programs, not your own.

[Mike Doty]

Prevent anyone on a network. "wait.dat" could be on the internet if TCP open is used.

FUNCTION PBMAIN () AS LONG
  OPEN "wait.dat" FOR BINARY AS #9999
  IF ERR THEN ? "Sorry, in use":EXIT FUNCTION
  ? "I'm running"
END FUNCTION

Post #1
Is there a simple method by which a program can ensure that there at any time is only one instance of "another program running?" Thanks in advance.

Post #4 says "my own program"

I want to do something to make sure that only one instance of my own program exists at any time (i.e. kill a second (third and so on ..) instance).

[Mike Doty]

Should also mention somebody could rename program and run it.

[John Petty]

I really don’t understand why there is so much code here that is not totally reliable for such a simple problem. Mutexes only work if you know how to create them as Global (no examples shown here for that) and then only on the local computer and the default namespace has yet again changed in 2008, same applies for matching window names, as for module checking as Mike says they only have to rename the program and of course none of the methods work if the program is being run by workstations sharing the data.
As an example on a 2003 server if a user logs on locally as say administrator and leaves a program running, then you log on as administrator using remote desktop the running program will not show even in task manager, you are in a different namespace.
The solution is incredibly simple, never allow two copies of the program to start.
In WINMAIN
ON ERROR RESUME NEXT
OPEN “c:\ not allowed.wtf” for binary LOCK READ WRITE as #1
If ERR = 70 EXIT FUNCTION
You can be nice if you like and give a message box.
Worried about network users then
OPEN \\shared drive\ etc
How easy can it get.

[Erik Christensen]

I apologize for having been somewhat unclear along the way. Thanks John for the wise comments and suggestions. I have really learned something.