time_based_metric.h

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/*
   Copyright (c) 2024, Oracle and/or its affiliates.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
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   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
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   This program is distributed in the hope that it will be useful,
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   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.
 
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#ifndef CS_MTA_TIME_BASED_METRIC
#define CS_MTA_TIME_BASED_METRIC
 
#include <atomic>
#include "time_based_metric_interface.h"
 
/// @brief Class that encodes how much time we waited for something
class Time_based_metric : public Time_based_metric_interface {
 public:
  /// @brief Constructor that allows you to define counting as being manual
  /// @param manual_counting shall count be automatic on start_timer or not
  /// (default false)
  explicit Time_based_metric(bool manual_counting = false);
 
  /// @brief Assignment operator
  /// @param other the object that is copied
  /// @return this object
  Time_based_metric &operator=(const Time_based_metric &other);
 
  /// @brief Deleted copy constructor, move constructor, move assignment
  /// operator.
  Time_based_metric(const Time_based_metric &) = delete;
  Time_based_metric(Time_based_metric &&) = delete;
  Time_based_metric &operator=(Time_based_metric &&) = delete;
 
  /// @brief Default destuctor.
  ~Time_based_metric() override = default;
 
  /// @brief Resets the counter and summed time to 0
  void reset() override;
 
  /// @brief Starts counting time we are waiting on something
  void start_timer() override;
 
  /// @brief Stops the timer for the wait.
  ///        Requires start_timer to be called first
  void stop_timer() override;
 
  /// @brief Returns the time waited across all executions of the start/stop
  /// methods
  /// @return The total time waited
  int64_t get_sum_time_elapsed() const override;
 
  /// @brief Increments the waiting counter
  void increment_counter() override;
 
  /// @brief Returns the number of time we waited on give spot
  /// @return the number of times waited
  int64_t get_count() const override;
 
 private:
  /// @brief Helper to get current time.
  /// @return Current time since the epoch for steady_clock, in nanoseconds.
  static int64_t now();
 
  /// The total nanoseconds of all completed waits, minus the absolute start
  /// time of an ongoing wait, if any.
  ///
  /// If there is no ongoing wait, this is nonnegative and is the correct
  /// metric. If there is an ongoing wait, this is negative, and the correct
  /// value is given by adding the current time to it:
  /// result = sum_of_completed_waits + current_time - start_of_current_wait
  std::atomic<int64_t> m_time{0};
  /// @brief The number of times we waited.
  std::atomic<int64_t> m_count{0};
 
  /// If false, the counter is incremented automatically by start_time, and the
  /// caller must not invoke increment_counter. If true, the counter is not
  /// incremented by start_time, so the caller has to invoke increment_counter.
  bool m_manual_counting{false};
};
 
#endif /* CS_MTA_TIME_BASED_METRIC */