MXS-2078 Add IntervalTimer

IntervalTimer is used for accumulating intervals (i.e. durations) over sections of code.

maxutils/maxbase/include/maxbase/stopwatch.hh

@@ -101,6 +101,40 @@ private:
     TimePoint m_lap;
 };
 
+/** IntervalTimer for accumulating intervals (i.e. durations). Do not expect many very short
+ *  durations to accumulate properly (unless you have a superfast processor, RTLinux, etc.)
+ *
+ * Usage pattern:
+ * IntervalTimer timer;  // created ahead of time.
+ * ...
+ * In some sort of a loop (explicit or implicit):
+ * timer.start_interval();
+ * foo();
+ * timer.end_interval();
+ * ...
+ * And finally:
+ * std::cout << timer.total() << std::endl;
+ *
+ */
+class IntervalTimer
+{
+public:
+    /** Create but do not start the intervaltimer, i.e. starting in paused mode. */
+    IntervalTimer();
+
+    /** Resume measuring time. Ok to call multiple times without an end_interval(). */
+    void start_interval();
+
+    /** Pause measuring time. */
+    void end_interval();
+
+    /** Total duration of intervals (thus far). */
+    Duration total() const;
+private:
+    TimePoint m_last_start;
+    Duration  m_total;
+};
+
 /** Returns the duration as a double and string adjusted to a suffix like ms for milliseconds.
  *  The double and suffix (unit) combination is selected to be easy to read.
  *  This is for output conveniece. You can always convert a duration to a specific unit:

maxutils/maxbase/src/stopwatch.cc

@@ -46,6 +46,27 @@ Duration StopWatch::restart()
     m_start = m_lap = now;
     return split;
 }
+
+IntervalTimer::IntervalTimer() : m_total(0)
+{
+}
+
+void IntervalTimer::start_interval()
+{
+    m_last_start = Clock::now();
+}
+
+void IntervalTimer::end_interval()
+{
+    m_total += Clock::now() - m_last_start;
+    // reset to make it easier to spot usage bugs, like calling end_interval(); end_interval();
+    m_last_start = TimePoint();
+}
+
+Duration IntervalTimer::total() const
+{
+    return m_total;
+}
 }   // maxbase
 
 /********** OUTPUT ***********/