tickconverter.inl

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//==================================================================================================
/// \file
/// This header-file is part of the \aliblong. It does not belong to an \alibmod and is
/// included in any \alibbuild.
///
/// \emoji :copyright: 2013-2025 A-Worx GmbH, Germany.
/// Published under \ref mainpage_license "Boost Software License".
//==================================================================================================
ALIB_EXPORT namespace alib {  namespace time {
 
//==================================================================================================
/// As explained in detail in the documentation of the module \alib_time, a steady time model is
/// supported with class \alib{time;Ticks} and a non-steady one representing the system clock with
/// class \alib{time;DateTime}.
/// Only values of the latter type can be converted to human-readable (calendar) date and time values.
///
/// In some situations however,software that requires steady, monotonic time points, may also be
/// required to present these time points in human-readable format. It is possible to do some sort
/// of conversion. For that, simply both clocks need to be probed at the same point
/// in time and then time points of both notions can be put in relation to these two probes.
///
/// The effect, however, is that the conversion results will change for all values as soon as
/// the system clock is changed and the probe values of the two clocks are updated.
/// This is true also for values that are "older" than the point in time that the clock change
/// happened. The reason is quickly understood: The system clock's counter changes, while the steady
/// clock's counter does not.
///
/// To give the user of \alib full control about how system clock changes are reflected,
/// the conversion of time points is encapsulated by this class together with one pair of clock probe
/// data. software can use one ore more instances of this class and update (synchronize) these
/// instances independently.
//==================================================================================================
class TickConverter
{
    protected:
        /// Time point of steady clock of last invocation of #SyncClocks.
        Ticks::TTimePoint       steadyClockSyncTime;
 
        /// Time point of system clock of last invocation of #SyncClocks.
        DateTime::TTimePoint    systemClockSyncTime;
 
    public:
        //==========================================================================================
        /// Constructor. Invokes #SyncClocks.
        //==========================================================================================
        TickConverter()
        {
            SyncClocks();
        }
 
        //==========================================================================================
        /// Generates a set of "probes" of the steady, monotonic clock and the system clock.
        /// The measurement of both clocks is repeated the given number of times and the pair with
        /// the smallest difference between both is chosen.
        /// This approach mitigates the risk of using a pair for which thread execution had been
        /// interrupted during the two measurements.
        ///
        /// Note that after a call to this method, the conversion methods may return slightly
        /// different values than before the call, even if the system clock was not changed.
        ///
        /// If this method is not invoked after a change of the system clock, such change of the
        /// system clock is not reflected by the conversion methods.
        /// In other words, the conversion methods always work just as if the system clock had not
        /// changed since the last invocation of this method.
        ///
        /// \note
        ///   On a GNU/Linux workstation (without workload), the error observed when doing only one
        ///   measurement was in the magnitude of several microseconds.
        ///
        /// @param qtyRepeats    The number of measurements to perform. Defaults to \c 5.
        //==========================================================================================
        ALIB_DLL
        void SyncClocks( int qtyRepeats = 5 );
 
        //==========================================================================================
        /// Sets the pair of conversion times to equal the other converter object. This is useful
        /// to avoid differences in conversion across converter instances used in software.
        ///
        /// @param other  Another converter object to copy the synchronization information from.
        //==========================================================================================
        void SetAs( const TickConverter& other )
        {
            steadyClockSyncTime= other.steadyClockSyncTime;
            systemClockSyncTime= other.systemClockSyncTime;
        }
 
        //==========================================================================================
        /// Converts a \b %Ticks object to a \b %DateTime object.
        /// @param ticks The ticks object to convert.
        /// @return The date time object.
        //==========================================================================================
        DateTime  ToDateTime( Ticks ticks )
        {
            return DateTime( systemClockSyncTime
                           + std::chrono::duration_cast<std::chrono::system_clock::duration>(
                                                         ticks.Export() - steadyClockSyncTime ) );
        }
 
        //==========================================================================================
        /// Converts a \b %DateTime object to a \b %Ticks object.
        /// @param dateTime The date/time object to convert.
        /// @return The date time object.
        //==========================================================================================
        Ticks  ToTicks( DateTime dateTime )
        {
            return Ticks( dateTime.Export() - systemClockSyncTime + steadyClockSyncTime);
        }
};
 
 
} // namespace alib[::time]
 
/// Type alias in namespace \b alib.
using   TickConverter= time::TickConverter;
 
}  // namespace [alib]