[core] Fix bug in frequency calculator that will reset the frequency …

…to 0.0 even though data is still incoming. (eclipse-ecal#1650)

ecal/core/src/util/frequency_calculator.h

@@ -1,6 +1,6 @@
-/* ========================= eCAL LICENSE =================================
+/* ========================= eCAL LICENSE =================================
  *
- * Copyright (C) 2016 - 2019 Continental Corporation
+ * Copyright (C) 2016 - 2024 Continental Corporation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -52,16 +52,16 @@ namespace eCAL
 
     FrequencyCalculator(const time_point& now_)
       : counted_elements(0)
-      , first_tick(now_)
-      , last_tick(now_)
+      , first_tick_time(now_)
+      , last_tick_time(now_)
       , previous_frequency(0.0)
     {
     }
 
     void addTick(const time_point& now)
     {
       counted_elements++;
-      last_tick = now;
+      last_tick_time = now;
     }
 
     double getFrequency()
@@ -71,16 +71,16 @@ namespace eCAL
         return previous_frequency;
       }
 
-      previous_frequency = calculateFrequency<T>(first_tick, last_tick, counted_elements);
-      first_tick = last_tick;
+      previous_frequency = calculateFrequency<T>(first_tick_time, last_tick_time, counted_elements);
+      first_tick_time = last_tick_time;
       counted_elements = 0;
       return previous_frequency;
     }
 
   private:
     long long counted_elements;
-    time_point first_tick;
-    time_point last_tick;
+    time_point first_tick_time;
+    time_point last_tick_time;
     double previous_frequency;
   };
 
@@ -105,22 +105,37 @@ namespace eCAL
       {
         calculator->addTick(now);
       }
-      last_tick = now;
+      last_tick_time = now;
+      received_tick_since_get_frequency_called = true;
     }
 
     double getFrequency(const time_point& now)
     {
       double frequency = calculator ? calculator->getFrequency() : 0.0;
 
+      // if the frequency is 0.0, return it right away
       if (frequency == 0.0)
       {
         return 0.0;
       }
 
-      // calculate theoretical frequency to detect timeouts;
-      double theoretical_frequency = calculateFrequency<T>(last_tick, now, 1);
-      // If the frequency is higher than reset_factor * theoretical_frequency, we reset. 
-      if (frequency >= theoretical_frequency * reset_factor)
+      // if we have received ticks, this means we don't want to reset the calculation
+      // so we return the frequency that the calculator has calculated
+      if (received_tick_since_get_frequency_called)
+      {
+        received_tick_since_get_frequency_called = false;
+        return frequency;
+      }
+
+      // if we have not received ticks since the last call of getFrequency
+      // then we calculate the  ΔT, e.g. the timespan in seconds between last received and next incoming element
+      // Based on the last time we received a tick we could calculate when we expect the next tick
+      // We can also calculate when we want to time out, based on the reset factor
+      // timeout = last_tick + ΔT * reset_factor
+      // If the current time is greater than the timeout time, we reset the calculator and return 0
+      auto expected_time_in_seconds_between_last_and_next_tick = std::chrono::duration<double>(1 / frequency);
+      time_point timeout_time = last_tick_time + std::chrono::duration_cast<std::chrono::nanoseconds>(expected_time_in_seconds_between_last_and_next_tick * reset_factor);
+      if (now > timeout_time)
       {
         calculator.reset();
         return 0.0;
@@ -131,7 +146,8 @@ namespace eCAL
 
   private:
     float reset_factor;
-    time_point last_tick;
+    time_point last_tick_time;
+    bool received_tick_since_get_frequency_called = false;
     std::unique_ptr<FrequencyCalculator<T>> calculator;
   };
 }

ecal/tests/cpp/util_test/src/util_test.cpp

@@ -1,6 +1,6 @@
 /* ========================= eCAL LICENSE =================================
  *
- * Copyright (C) 2016 - 2019 Continental Corporation
+ * Copyright (C) 2016 - 2024 Continental Corporation
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -194,3 +194,56 @@ TEST(core_cpp_util, Freq_ResettableFrequencyCalculator)
     }
   }
 }
+
+
+struct command
+{
+  std::string command_type;
+  long long time_point;
+};
+
+std::vector<command> commands =
+{
+command{"getting frequency", 0 },
+command{"ticking", 500         },
+command{"getting frequency", 1000 },
+command{"ticking", 1500         },
+command{"getting frequency", 2000 },
+command{"ticking", 2500         },
+command{"getting frequency", 3000 },
+command{"ticking", 3998         },
+command{"getting frequency", 4000 },
+command{"ticking", 4002         },
+command{"getting frequency", 5000 },
+command{"ticking", 5998         },
+command{"getting frequency", 6000 },
+};
+
+TEST(core_cpp_util, Freq_NoZeroFrequency)
+{
+  eCAL::ResettableFrequencyCalculator<std::chrono::steady_clock> calculator(3.0f);
+  int i = 0;
+
+  for (const auto& command : commands)
+  {
+    std::chrono::steady_clock::time_point time(std::chrono::milliseconds(command.time_point));
+
+    if (command.command_type == "ticking")
+    {
+      calculator.addTick(time);
+    }
+    else if (command.command_type == "getting frequency")
+    {
+      auto frequency = calculator.getFrequency(time);
+      if (i > 1)
+      {
+        ASSERT_GT(frequency, 0.0) << "Iteration " << i;
+      }
+
+      ++i;
+    }
+    else
+    {
+    }
+  }
+}