...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Inform the thread pool that some work is no longer outstanding.
void on_work_finished() const;
This function is used to inform the thread pool that some work has finished.
Once the count of unfinished work reaches zero, the thread pool's join()
function is permitted to exit.