Ensuring only one instance of a program – how?

[Michael Mattias]

You are assuming that this type of code will be used only to determine if your own application is already running.

Actually, I was assuming it would be used to determine if an instance of THIS program was running... which was, after all, the original question.

MCM

[David Roberts]

Re your version 2 Erik

' This version will is based on the file size. It will kill instances with the
' same file size even if the file has been renamed by someone.
.....
.....
.....
IF DirDataVar.FileSizeLow = FileSize AND lngR <> kk THEN ' kill other files of same size even if renamed.

Before killing I'd be inclined to make sure that they have the same SHA1 hash value.

[Graham McPhee]

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

You are assuming that this type of code will be used only to determine if your own application is already running.

The scope of the code I wrote was to cover detection of multiple instances of selected applications, SQL Query analyser for example, that I had no control over the launching of; but might still cause my application problems when it is trying to apply tsql scripts to one or more databases.

[Mike Doty]

Synonyms
charisma, dash, flare, style, swagger, élan, flair, flourish, verve, vigor,

[Michael Mattias]

The file solution is awfully straightforward.... but if you don't need the panache points......

[Mike Doty]

To make it more useful, the locked file can contain the computer name and time the file was locked.
Makes it much easier on a network to see who is holding up production.

[Erik Christensen]

Mike, your suggestion was fine.

[Michael Mattias]

>What was wrong with my suggestion

Nothing. Testing a file either for 'existence' or 'in use' is a perfectly valid way to check if a program is running.

MCM

[Mike Doty]

What was wrong with my suggestion

[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.

[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.

[Mike Doty]

Should also mention somebody could rename program and run it.

[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).

[Erik Christensen]

I am talking about other programs, not your own.

[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]

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

[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

[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

[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

[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