透過CreateMutexA函式建立一個互斥體，然後用GetLastError來獲取返回值判斷是否重複開啟同一個應用。

外部函式宣告

Function ulong CreateMutexA (ulong lpMutexAttributes, int bInitialOwner, ref string lpName) library "kernel32.dll"

Function ulong GetLastError () library "kernel32.dll"

APP的open事件程式碼

string ls_mutex_name

long ll_mutex

long ll_err

if handle (GetApplication(),false) 0 then

ls_mutex_name = this.AppName

ll_mutex = CreateMutexA (0,0,ls_mutex_name)

ll_err = GetLastError ()

if ll_err = 183 then

messagebox("","程式重複開啟")

Halt close

end if

end if

open(w_open)