std::atomic_flag::clear
From cppreference.com
                    
                                        
                    < cpp | atomic | atomic flag
                    
                                                            
                    |   Defined in header <atomic>
   | 
||
|   void clear( std::memory_order order = std::memory_order_seq_cst ) volatile;  | 
(1) | (since C++11) | 
|   void clear( std::memory_order order = std::memory_order_seq_cst );  | 
(2) | (since C++11) | 
Atomically changes the state of a std::atomic_flag to clear (false).
[edit] Parameters
| order | - | the memory sycnhronization ordering for this operation | 
[edit] Exceptions
[edit] See also
|    atomically sets the flag to true and obtains its previous value   (public member function)  | |
|    (C++11) (C++11)  | 
   atomically sets the value of the flag to false   (function)  | 
|    (C++11)  | 
   defines memory ordering constraints for the given atomic operation   (typedef)  |