work_thread_activity.hpp

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/*
 * SObjectizer-5
 */
 
/*!
 * \file
 * \brief Data types for work thread's activity stats.
 *
 * \since v.5.5.18
 */
 
#pragma once
 
#include <cstdint>
#include <chrono>
#include <iostream>
#include <optional>
#include <type_traits>
 
namespace so_5
{
 
namespace stats
{
 
/*!
 * \brief An alias for clock type to be used for statistics.
 *
 * \since v.5.5.18
 */
using clock_type_t = std::conditional<
        std::chrono::high_resolution_clock::is_steady,
        std::chrono::high_resolution_clock,
        std::chrono::steady_clock
    >::type;
 
static_assert( clock_type_t::is_steady,
    "clock_type_t must be steady clock!" );
 
/*!
 * \brief An alias for type for representing time duration.
 *
 * \since v.5.5.18
 */
using duration_t = clock_type_t::duration;
 
/*!
 * \brief Statistics of some activity.
 *
 * \since v.5.5.18
 */
struct activity_stats_t
  {
    //! Count of events in that period of time.
    std::uint_fast64_t m_count{};
 
    //! Total time spent for events in that period of time.
    duration_t m_total_time{};
 
    //! Average time for one event.
    duration_t m_avg_time{};
 
    //! Duration of the current activity.
    //!
    //! This value is defined only if the current activity is present.
    //! Otherwise it will be nullopt.
    //!
    //! When it isn't nullopt it contains duration of the current
    //! activity. For example, the total execution time of the current
    //! event handler. If an instance of activity_stats_t describes
    //! waiting, then this field shows duration of the current waiting
    //! period.
    //!
    //! \since v.5.8.5
    std::optional< duration_t > m_current_activity_time;
  };
 
/*!
 * \brief Helper for printing value of activity_stats.
 *
 * \since v.5.5.18
 */
inline std::ostream &
operator<<( std::ostream & to, const activity_stats_t & what )
{
  auto to_ms = []( const duration_t & d ) {
    return double(std::chrono::duration_cast< std::chrono::nanoseconds >( d )
        .count()) / 1000000.0;
  };
 
  to << "[count=" << what.m_count
    << ";total=" << to_ms(what.m_total_time)
    << "ms;avg=" << to_ms(what.m_avg_time) << "ms";
  if( what.m_current_activity_time )
    to << ";current=" << to_ms(*what.m_current_activity_time) << "ms";
  to << ']';
 
  return to;
}
 
/*!
 * \brief Stats for a work thread activity.
 *
 * \since v.5.5.18
 */
struct work_thread_activity_stats_t
  {
    //! Stats for processed events.
    activity_stats_t m_working_stats{};
 
    //! Stats for waiting periods.
    /*!
     * \note
     * Not all dispatchers can provide this information. In such a case
     * there will be an object without actual information (all fields of
     * m_waiting_stats will have default zero values).
     */
    activity_stats_t m_waiting_stats{};
  };
 
namespace details
{
 
/*!
 * \brief A function for calculating average value.
 *
 * Uses modified moving average (also known as running moving average)
 * which is calculated as: MMA(t) = (last + (N-1)*MMA(t-1))/N.
 *
 * \since v.5.5.18
 */
inline duration_t
calc_avg_time(
  //! Total count of samples.
  std::uint_fast64_t count,
  //! Previous average value.
  duration_t previous,
  //! Duration of last activity (or waiting).
  duration_t last )
{
  const int N = count > 100u ? 100 : (count ? static_cast< int >(count) : 1);
  return (last + (N-1) * previous) / N;
}
 
/*!
 * \brief Helper function for simplification of current stats update.
 *
 * \since v.5.5.18
 */
inline void
update_stats_from_duration(
  activity_stats_t & value_to_update,
  clock_type_t::duration last_duration )
{
  value_to_update.m_total_time += last_duration;
  value_to_update.m_avg_time = calc_avg_time(
      value_to_update.m_count,
      value_to_update.m_avg_time, last_duration );
}
 
/*!
 * \brief Helper function for simplification of current stats update.
 *
 * \since v.5.5.18
 */
inline void
update_stats_from_current_time(
  activity_stats_t & value_to_update,
  clock_type_t::time_point activity_started_at )
{
  const auto current_activity_time =
      clock_type_t::now() - activity_started_at;
  value_to_update.m_current_activity_time = current_activity_time;
  update_stats_from_duration(
      value_to_update,
      current_activity_time );
}
 
} /* namespace details */
 
} /* namespace stats */
 
} /* namespace so_5 */