absl::Barrier

Description

This class creates a barrier which blocks threads until a prespecified threshold of threads (num_threads) utilizes the barrier. A thread utilizes the Barrier by calling Block() on the barrier, which will block that thread; no call to Block() will return until num_threads threads have called it.

Exactly one call to Block() will return true, which is then responsible for destroying the barrier; because stack allocation will cause the barrier to be deleted when it is out of scope, barriers should not be stack allocated.

Example:

// Main thread creates a `Barrier`:
barrier = new Barrier(num_threads);

// Each participating thread could then call:
if (barrier->Block()) delete barrier;  // Exactly one call to `Block()`
                                        // returns `true`; that call
                                        // deletes the barrier.