Sampling period for computing the rolling average real time factor (#758)

* Introduced cosim::real_time_config.step_duration_to_monitor for computing the rolling average real time factor using the specified period in second.

* Local variable naming change.

* Addressed comments

* Additional fix

* Using duration_cast

Author: davidhjp01

include/cosim/timer.hpp

@@ -36,6 +36,15 @@ struct real_time_config
      * This value is used for monitoring purposes only.
      */
     std::atomic<int> steps_to_monitor = 5;
+
+    /**
+     *  A sampling period in real time (wall clock) in milliseconds used in the rolling average real time factor calculation.
+     *  This can be useful when simulation step size is small and a fixed value for `steps_to_monitor`
+     *  would not compute an accurate rolling average real time factor.
+     *  When the value is greater than zero, the real time factor is computed periodically using the
+     *  specified time instead of the `steps_to_monitor` value.
+     */
+    std::atomic<std::chrono::milliseconds> sampling_period_to_monitor = std::chrono::milliseconds(-1);
 };
 
 } // namespace cosim
@@ -54,6 +63,7 @@ class hash<cosim::real_time_config>
         boost::hash_combine(seed, v.real_time_simulation.load());
         boost::hash_combine(seed, v.real_time_factor_target.load());
         boost::hash_combine(seed, v.steps_to_monitor.load());
+        boost::hash_combine(seed, v.sampling_period_to_monitor.load().count());
         return seed;
     }
 };

src/cosim/timer.cpp

@@ -7,7 +7,6 @@
 
 #include <chrono>
 #include <thread>
-
 typedef std::chrono::steady_clock Time;
 constexpr std::chrono::microseconds MIN_SLEEP(100);
 
@@ -37,6 +36,12 @@ class real_time_timer::impl
         const auto newHash = std::hash<real_time_config>()(*config_);
         if (newHash != configHashValue_) {
             start(currentTime);
+            const auto sampling_period = config_->sampling_period_to_monitor.load();
+            if (sampling_period.count() > 0) {
+                sampling_period_to_monitor_ = sampling_period;
+            } else {
+                sampling_period_to_monitor_ = std::nullopt;
+            }
             configHashValue_ = newHash;
         }
         double rtfTarget = config_->real_time_factor_target.load();
@@ -72,21 +77,39 @@ class real_time_timer::impl
     std::shared_ptr<real_time_config> config_;
     size_t configHashValue_;
     std::shared_ptr<real_time_metrics> metrics_;
+    std::optional<std::chrono::milliseconds> sampling_period_to_monitor_ = std::nullopt;
+
+    template<typename Rep, typename Period>
+    void update_rolling_average_real_time_factor(
+        const Time::time_point& currentTime,
+        const time_point& currentSimulationTime,
+        const std::chrono::duration<Rep, Period>& elapsedRealTime)
+    {
+        const auto elapsedSimTime = currentSimulationTime - rtSimulationStartTime_;
+
+        metrics_->rolling_average_real_time_factor =
+            std::chrono::duration_cast<cosim::duration>(elapsedSimTime).count() / (1.0 * std::chrono::duration_cast<cosim::duration>(elapsedRealTime).count());
+        rtStartTime_ = currentTime;
+        rtSimulationStartTime_ = currentSimulationTime;
+        rtCounter_ = 0L;
+    }
 
     void update_real_time_factor(Time::time_point currentTime, time_point currentSimulationTime)
     {
-        const auto relativeSimTime = currentSimulationTime - simulationStartTime_;
-        const auto relativeRealTime = currentTime - startTime_;
+        const auto relativeSimTime =  std::chrono::duration_cast<cosim::duration>(currentSimulationTime - simulationStartTime_);
+        const auto relativeRealTime =  std::chrono::duration_cast<cosim::duration>(currentTime - startTime_);
         metrics_->total_average_real_time_factor = relativeSimTime.count() / (1.0 * relativeRealTime.count());
 
-        if (rtCounter_ >= config_->steps_to_monitor.load()) {
-            const auto elapsedSimTime = currentSimulationTime - rtSimulationStartTime_;
+        if (sampling_period_to_monitor_.has_value()) {
             const auto elapsedRealTime = currentTime - rtStartTime_;
 
-            metrics_->rolling_average_real_time_factor = elapsedSimTime.count() / (1.0 * elapsedRealTime.count());
-            rtStartTime_ = currentTime;
-            rtSimulationStartTime_ = currentSimulationTime;
-            rtCounter_ = 0L;
+            if (elapsedRealTime > sampling_period_to_monitor_.value()) {
+                const auto elapsedSimTime = currentSimulationTime - rtSimulationStartTime_;
+                update_rolling_average_real_time_factor(currentTime, currentSimulationTime, elapsedRealTime);
+            }
+        } else if (rtCounter_ >= config_->steps_to_monitor.load()) {
+            const auto elapsedRealTime = currentTime - rtStartTime_;
+            update_rolling_average_real_time_factor(currentTime, currentSimulationTime, elapsedRealTime);
         }
         rtCounter_++;
     }