C # The application can only be opened once, and only one application can be opened. The application cannot be opened repeatedly.

ModifyProgram **************************************** ***** Using system; Using system. Collections. Generic; Using system. Windows. forms; Using system. Threading; namespace pcbilling_server {< br> static class Program {< br> Public static bool bonlyoneinstance = false; /// // main entry point of the application. // [stathread] static void main () {< br> bonlyoneinstance = false; mutex = new mutex (true, application. userappdatapath. replace (@ "/", "_"), Out bonlyoneinstance); If (! Bonlyoneinstance) {< br> MessageBox. Show ("the system is running! "," Message ", messageboxbuttons. OK, messageboxicon. information); system. environment. exit (0); return; } application. enablevisualstyles (); application. setcompatibletextrenderingdefault (false); application. run (New frm_login (); }< BR >}