std::experimental::latch::wait
From cppreference.com
                    
                                        
                    < cpp | experimental | latch
                    
                                                            
                    | void wait() const; | (1) | (concurrency TS) | 
Blocks the calling thread until the internal counter reaches 0. If it is zero
already, returns immediately.
Parameters
(none)
Return value
(none)
Exceptions
Throws nothing.