Run only one instance of your application: Difference between revisions

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The question on how to make sure that your application is only started once by your users can be approached in several ways.
The question on how to make sure that your application is only started once by your users can be approached in several ways.


1. Using mutexes
# Using mutexes
2. Using FindWindow WinAPI
# Using FindWindow WinAPI


=== Using mutexes ===
=== Using mutexes ===
Line 11: Line 11:


In the SRC file within the panel object put this piece of code:
In the SRC file within the panel object put this piece of code:
Procedure Exit_Application
<pre>
Procedure Exit_Application
     integer iVoid
     integer iVoid
     If (ghMuteX) Move (CloseHandle(ghMutex)) to iVoid
     If (ghMuteX) Move (CloseHandle(ghMutex)) to iVoid
     move 0 to ghMuteX
     move 0 to ghMuteX
     Forward Send Exit_Application
     Forward Send Exit_Application
End_Procedure
End_Procedure
</pre>
And in a package that gets hit on startup:
And in a package that gets hit on startup:
// Constants
<pre>
Define ERROR_INVALID_HANDLE        for 6    //  taken from error.h of VS7
// Constants
Define ERROR_ALREADY_EXISTS        for 183<br/>
Define ERROR_INVALID_HANDLE        for 6    //  taken from error.h of VS7
Handle ghMuteX<br/>
Define ERROR_ALREADY_EXISTS        for 183<br/>
// external functions
Handle ghMuteX<br/>
#IFNDEF Get_CreateMuteX
// external functions
    External_Function CreateMuteX "CreateMutexA" Kernel32.dll Integer i1 Integer i2 Integer i3 Returns Integer
#IFNDEF Get_CreateMuteX
#ENDIF
    External_Function CreateMuteX "CreateMutexA" Kernel32.dll Integer i1 Integer i2 Integer i3 Returns Integer
#IFNDEF Get_CloseHandle
#ENDIF
    External_Function CloseHandle "CloseHandle" Kernel32.dll Integer i1 Returns Integer
#IFNDEF Get_CloseHandle
#ENDIF<br/>
  External_Function CloseHandle "CloseHandle" Kernel32.dll Integer i1 Returns Integer
// function to create a mutex
#ENDIF<br/>
Procedure Create_MuteX_Object
// function to create a mutex
    Integer iVoid iErr
Procedure Create_MuteX_Object
    String sID
  Integer iVoid iErr
    Move "Unique String For My Application" To sID
  String sID
    Move (CreateMuteX(0,1,AddressOf(sID))) To ghMuteX
  Move "Unique String For My Application" To sID
    If (ghMuteX <> ERROR_INVALID_HANDLE) Begin
  Move (CreateMuteX(0,1,AddressOf(sID))) To ghMuteX
        Move (GetLastError()) To iErr
  If (ghMuteX <> ERROR_INVALID_HANDLE) Begin
        If (iErr = ERROR_ALREADY_EXISTS) Begin  // program is already  
      Move (GetLastError()) To iErr
                                                // running
      If (iErr = ERROR_ALREADY_EXISTS) Begin  // program is already  
            Move (CloseHandle(ghMuteX)) To iVoid
                                              // running
            Move 0 To ghMuteX
          Move (CloseHandle(ghMuteX)) To iVoid
            // kill the application here if you do not want to allow  
          Move 0 To ghMuteX
            // multiple instances
          // kill the application here if you do not want to allow  
            ABORT
          // multiple instances
        End
          ABORT
        Else Send None  // program is not already running
      End
    End
      Else Send None  // program is not already running
    Else Send None  // rare error; object could not be created
  End
End_Procedure  // Create_MuteX_Object<br/>
  Else Send None  // rare error; object could not be created
// create the mutex
End_Procedure  // Create_MuteX_Object<br/>
Send Create_MuteX_Object
// create the mutex
Send Create_MuteX_Object
</pre>


=== Using FindWindow WinAPI ===
=== Using FindWindow WinAPI ===
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Usage in SRC:
Usage in SRC:
 
<pre>
  Use myPanel,pkg
  Use myPanel,pkg
  Object Main is a myPanel
  Object Main is a myPanel
 
</pre>


Source myPanel.pkg
Source myPanel.pkg
<pre>
  ////////////////////////////////////////////
  ////////////////////////////////////////////
  //
  //
Line 99: Line 104:
       End_Procedure // End_Construct_Object
       End_Procedure // End_Construct_Object
  End_class
  End_class
</pre>


The FindWindow technique is also discussed in the book [http://www.starzen.com/Products/DataFlexVDF/Books/tabid/56/Default.aspx Mastering Visual DataFlex] from Starzen.
The FindWindow technique is also discussed in the book [http://www.starzen.com/Products/DataFlexVDF/Books/tabid/56/Default.aspx Mastering Visual DataFlex] from Starzen.


[[Category: How To]]
[[Category: Tutorials]]

Revision as of 23:14, 10 December 2007

The question on how to make sure that your application is only started once by your users can be approached in several ways.

  1. Using mutexes
  2. Using FindWindow WinAPI

Using mutexes

Dalton Pulsipher says: "We use a MuteX object to do this. Just attach one to your program and on startup check if it already exists on the system. Here is the code if you want to go that route."

In the SRC file within the panel object put this piece of code:

Procedure Exit_Application
    integer iVoid
    If (ghMuteX) Move (CloseHandle(ghMutex)) to iVoid
    move 0 to ghMuteX
    Forward Send Exit_Application
End_Procedure

And in a package that gets hit on startup:

// Constants
Define ERROR_INVALID_HANDLE        for 6    //  taken from error.h of VS7
Define ERROR_ALREADY_EXISTS        for 183<br/>
Handle ghMuteX<br/>
// external functions
#IFNDEF Get_CreateMuteX
    External_Function CreateMuteX "CreateMutexA" Kernel32.dll Integer i1 Integer i2 Integer i3 Returns Integer
#ENDIF
#IFNDEF Get_CloseHandle
   External_Function CloseHandle "CloseHandle" Kernel32.dll Integer i1 Returns Integer
#ENDIF<br/>
// function to create a mutex
Procedure Create_MuteX_Object
   Integer iVoid iErr
   String sID
   Move "Unique String For My Application" To sID
   Move (CreateMuteX(0,1,AddressOf(sID))) To ghMuteX
   If (ghMuteX <> ERROR_INVALID_HANDLE) Begin
       Move (GetLastError()) To iErr
       If (iErr = ERROR_ALREADY_EXISTS) Begin  // program is already 
                                               // running
           Move (CloseHandle(ghMuteX)) To iVoid
           Move 0 To ghMuteX
           // kill the application here if you do not want to allow 
           // multiple instances
           ABORT
       End
       Else Send None  // program is not already running
   End
   Else Send None  // rare error; object could not be created
End_Procedure  // Create_MuteX_Object<br/>
// create the mutex
Send Create_MuteX_Object

Using FindWindow WinAPI

Leslie Brennan says:

Usage in SRC:

 Use myPanel,pkg
 Object Main is a myPanel

Source myPanel.pkg

 ////////////////////////////////////////////
 //
 // 05/24/2007 
 // Panel Class from Pieter van Dieren to check
 // to make sure program is only run one time.
 //
 /////////////////////////////////////////////

 Use dfPanel.pkg

 Class myPanel is a Panel
    // DoCheckProgramActive
    // Checks if the program already is active.
    // If so, it activates the running application and closes this one.
      Procedure DoCheckProgramActive
        String sTitle
        Handle hWnd
        Integer iVoid

        Register_Object Main
        Get Label of Main to sTitle
        Move (FindWindow("",sTitle))  to hWnd
        If (hWnd) Begin
          Send Stop_Box (sTitle + " Already is Running and Can only be Started Once.") "Error:"
          Move (ShowWindow(hWnd,SW_MAXIMIZE)) to iVoid  // 9 =SW_RESTORE SW_NORMAL
          Move (SetForegroundWindow(hWnd)) to iVoid
          Abort
        End
      End_Procedure // DoCheckProgramActive

      // End_Construct_Object
      Procedure End_Construct_Object
        Send DoCheckProgramActive
        Forward Send End_Construct_Object
      End_Procedure // End_Construct_Object
 End_class

The FindWindow technique is also discussed in the book Mastering Visual DataFlex from Starzen.