RateLimiter.hpp

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#ifndef DATAHANDLINGLIBS_INCLUDE_DATAHANDLINGLIBS_UTILS_RATELIMITER_HPP_
#define DATAHANDLINGLIBS_INCLUDE_DATAHANDLINGLIBS_UTILS_RATELIMITER_HPP_
 
#include <atomic>
#include <chrono>
#include <ctime>
#include <unistd.h>
 
namespace dunedaq {
namespace datahandlinglibs {

class RateLimiter
{
public:
  using timestamp_t = std::uint64_t; // NOLINT(build/unsigned)
  static inline constexpr timestamp_t ns = 1;
  static inline constexpr timestamp_t us = 1000 * ns;
  static inline constexpr timestamp_t ms = 1000 * us;
  static inline constexpr timestamp_t s = 1000 * ms;
 
  explicit RateLimiter(double kilohertz)
    : m_max_overshoot(10 * ms)
  {
    adjust(kilohertz);
    init();
  }
 
  void init()
  {
    m_now = gettime();
    m_deadline = m_now + m_period.load();
  }

  void adjust(double kilohertz)
  {
    m_kilohertz.store(kilohertz);
    m_period.store(static_cast<timestamp_t>((1000.f / m_kilohertz) * static_cast<double>(us)));
  }
 
  void limit()
  {
    m_now = gettime();
    if (m_now > m_deadline + m_max_overshoot) {
      m_deadline = m_now + m_period.load();
    } else {
      if (m_now < m_deadline) {
        if (m_deadline - m_now > 0) {
          timespec tim;
          tim.tv_sec = 0;
          tim.tv_nsec = m_deadline - m_now;
          // The second argument will be overwritten but we
          // do not care about this temporary variable
          nanosleep(&tim, &tim);
          m_now = gettime();
        }
        while (m_now < m_deadline) {
            m_now = gettime();
        }
      }
      m_deadline += m_period.load();
    }
  }
 
protected:
  timestamp_t gettime()
  {
    ::timespec ts;
    ::clock_gettime(CLOCK_MONOTONIC, &ts);
    return timestamp_t(ts.tv_sec) * s + timestamp_t(ts.tv_nsec) * ns;
  }
 
private:
  std::atomic<double> m_kilohertz;
  timestamp_t m_max_overshoot;
  std::atomic<timestamp_t> m_period;
  timestamp_t m_now;
  timestamp_t m_deadline;
};
 
} // namespace datahandlinglibs
} // namespace dunedaq
 
#endif // DATAHANDLINGLIBS_INCLUDE_DATAHANDLINGLIBS_UTILS_RATELIMITER_HPP_