33 Concurrency support library [thread]

33.9 Coordination types [thread.coord]

33.9.2 Latches [thread.latch] General [thread.latch.general]

A latch is a thread coordination mechanism that allows any number of threads to block until an expected number of threads arrive at the latch (via the count_down function).
The expected count is set when the latch is created.
An individual latch is a single-use object; once the expected count has been reached, the latch cannot be reused.