【trick】A variant of token bucket implementation

struct TokenBucket
{
  uint64_t fill_interval_;
  uint64_t gen_interval_;
  uint64_t reset_time_;
  // reset_time_ is equivalent to last_consume_time + token_num and
  // the calculated token num is auto renormalized on limit change.
  
  TokenBucket()
  : fill_interval_(0)
  , gen_interval_(0)
  , reset_time_(0) {}
  
  // eg, for 10req/30s, capacity=10, period=30
  void set_limit(uint64_t capacity, uint64_t period)
  {
    fill_interval_ = period;
    gen_interval_ = period / capacity;
  }
  
  bool consume(unsigned num)
  {
    uint64_t curr_time = get_monotonic_time();
    uint64_t new_reset_time = std::max(reset_time_, curr_time - fill_interval_) + gen_interval_ * num;
    if (curr_time >= new_reset_time)
    {
      reset_time_ = new_reset_time; // reset_time_ is monotonic increasing
      return true;
    }
    return false;
  }
};