call_once
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | Defined in header  <threads.h> | ||
| void call_once( once_flag* flag, void (*func)(void) ); | (since C11) | |
Calls function func exactly once, even if invoked from several threads.
The completion of the function func synchronizes with all previous or subsequent calls to call_once with the same flag variable.
[edit] Parameters
| flag | - | pointer to an object that is used to ensure funcis called only once | 
| func | - | the function to execute | 
[edit] Return value
(none)


