Lock-free queue using a ring buffer on the stack

Example

#include <lockfree_ring.h>
// consumer threads:
void consumer(vir::lockfree_ring<Data> &q)
{
  while (keep_running) {
    auto popper = q.pop_front();
    for (;;) {
      std::optional<Data> data = popper.get();
      if (data) {
        do_work(data.value);
        break;
      }
      do_something_else();
    }
  }
}
// producer threads:
void producer(vir::lockfree_ring<Data> &q)
{
  while (keep_running) {
    Data data = produce_data();
    auto pusher = q.prepare_push(std::move(data));
    while (!pusher.try_push()) {
       do_something_else();
    }
  }
}

Remarks

There is little guarantee about ordering and no guarantee about fairness.
However, if the size of the ring is larger than the number of active reader
objects (returned from pop_front()) then all consumers will eventually be
able to read a value (unless one of the writers does not fill its pusher
object).