atomic_flag
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  
<stdatomic.h>
  | 
||
|   typedef /* unspecified */ atomic_flag; 
 | 
(since C11) | |
atomic_flag is an atomic boolean type. Unlike other atomic types, it is guaranteed to be lock-free. Unlike atomic_bool, atomic_flag does not provide load or store operations.