Sometimes users click several times on the same icon and run several instances of program.
To prevent it you can create a global atom when starting your program if it does not exist yet.
(Global atoms are string variables for all Windows applications)


-- FirstIdle script for first page
to handle FirstIdle  
	system logical myFirstEnter
	system int myAtom

	linkdll "USER"
		INT GlobalFindAtom(STRING)
		INT GlobalAddAtom(STRING)
		INT GlobalDeleteAtom(INT)
	end

	myText = "My program already here" -- Here might be any text - it is global string variable for all Windows applications
	get GlobalFindAtom(myText)
	if It <> 0 -- This global atom already exists
		request "Another instance of this program already exists or this program was finished incorrectly." & CRLF & "Run this program again?" with "Yes" or "No"
		if It = "No"
			send Exit to this book
			break to system
		else
			myFirstEnter = false
		end if
	else  -- Create global atom
		myAtom = GlobalAddAtom(myText)
		myFirstEnter = true
	end if
end


-- Exit script for book
to handle Exit
	system int myAtom
	system logical myFirstEnter

	if myFirstEnter = true --This is a first instance
		get GlobalDeleteAtom(myAtom)
	end if
	forward
end