Allow only Single instance, blitz+ blitz3d

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Allow only Single instance, blitz+ blitz3d by Dan

2015

Here is the code which checks if the Program is allready running on the windows systems.
Put it at the beginning of your program.

It is usefull for screensavers and other programs where only one instance should run.

(got this from the german blitzbasic forum )

So here is a copy for the blitzbasic forum.

;kernel32.decls:

;.lib "kernel32.dll"
; CreateMutex%(lpMutexAttributes%,bInitialOwner%,lpName$):"CreateMutexA"
; api_GetLastError% () : "GetLastError"
; api_ReleaseMutex%(Handle%):"ReleaseMutex"
;
; Note: My system allready has api_CreateMutex% (lpMutexAttributes*, bInitialOwner%, lpName$) : "CreateMutexA" in Kernel32.decls but it crashes the app. The above Function works.

	Const ERROR_ALREADY_EXISTS=183
	hMutex=CreateMutex(0,1,"Change this for different programs") ; Mutex accessible to any program, change it for other programs 
	If api_GetLastError() = ERROR_ALREADY_EXISTS Then
	
	    Print "Sorry allready running!" ; Remove this line, it is only for this demo
	    Delay 5000                      ; Remove this line, it is only for this demo
	
		End ; End the app
	EndIf
	
	Print " Working ! "
	Print "Start me again to check if this demo is working correctly"
	Print "Remember to''Change this for different programs'' text "
	Print " so your apps have an unique mutex assigned"
	Repeat 
	Until KeyDown(1)
;At the end of your program release the Mutex with: 	
	api_ReleaseMutex(hMutex)
	
	End

;**********************************************************

;Edit 15.6.2016:    Mutex as function, simplifies the usage.

Function Mutex(MutexName$="")
;To set a mutex, enter a name
;call it again without parameters to end the duplicate start!

;Copy following lines at the beginning of your program and uncomment
;Const ERROR_ALREADY_EXISTS=183			;For mutex
;Global hMutex

;example run:
;If Mutex("My Saver C")=1 Then Mutex() ;Prevents multiple instances 
    
	If Len(MutexName$)>0
		hMutex=CreateMutex(0,1,MutexName$) ; Mutex accessible to any program, change it for other programs 
		If api_GetLastError() = ERROR_ALREADY_EXISTS Then Return 1
	Else
		api_ReleaseMutex(hMutex)
		End 						;To end or not to end ?!?
	EndIf
End Function

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