std::recursive_mutex::unlock
From cppreference.com
                    
                                        
                    < cpp | thread | recursive mutex
                    
                                                            
                    
|   void unlock();  | 
(since C++11) | |
Unlocks the mutex if its level of ownership is 1 (there was exactly one more call to lock() than there were calls to unlock() made by this thread), reduces the level of ownership by 1 otherwise.
The mutex must be locked by the current thread of execution, otherwise, the behavior is undefined.
This operation synchronizes-with (as defined in std::memory_order) any subsequent lock operation that obtains ownership of the same mutex.
Parameters
(none)
Return value
(none)
Exceptions
Throws nothing.
Notes
unlock() is usually not called directly: std::unique_lock and std::lock_guard are used to manage exclusive locking.
Example
| This section is incomplete Reason: no example  | 
See also
|   locks the mutex, blocks if the mutex is not available  (public member function)  | |
|   tries to lock the mutex, returns if the mutex is not available  (public member function)  | |
|   C documentation for mtx_unlock 
 | |