std::experimental::barrier::barrier (3) - Linux Man Pages
explicit barrier( std::ptrdiff_t num_threads ); (1) (concurrency TS)
barrier( const barrier & ) = delete; (2) (concurrency TS)
1) Constructs a barrier for num_threads participating threads. The set of participating threads is the first num_threads threads to arrive at the synchronization point.
2) Copy constructor is deleted; barrier is not copyable.
num_threads - the number of participating threads for the barrier; must be non-negative
If num_threads is zero, the set of participating threads is empty, and barrier can only be destroyed.