Make time more precise on platforms that have CLOCK_MONOTONIC (otherwise, we'll only have second-level precision)

moses/src/Timer.cpp

@@ -15,9 +15,17 @@ namespace Moses
  */
 double Timer::elapsed_time()
 {
+#ifdef CLOCK_MONOTONIC
+  struct timespec now;
+  clock_gettime(CLOCK_MONOTONIC, &now);
+  double elapsed = (now.tv_sec - start_time.tv_sec);
+  elapsed += (now.tv_nsec - start_time.tv_nsec) / 1000000000.0;
+  return elapsed;
+#else
   time_t now;
   time(&now);
   return difftime(now, start_time);
+#endif
 }
 
 /***
@@ -48,7 +56,11 @@ void Timer::start(const char* msg)
   running = true;
 
   // Set the start time;
+#ifdef CLOCK_MONOTONIC
+  clock_gettime(CLOCK_MONOTONIC, &start_time);
+#else
   time(&start_time);
+#endif
 }
 
 /***

moses/src/Timer.h

@@ -10,6 +10,9 @@ namespace Moses
 {
 
 /** Wrapper around time_t to time how long things have been running
+ *  according to walltime. We avoid CPU time since it is less reliable
+ *  in a multi-threaded environment and can spuriously include clock cycles
+ *  used by other threads in the same process.
  */
 class Timer
 {
@@ -17,7 +20,13 @@ class Timer
 
 private:
   bool running;
+  // note: this only has the resolution of seconds, we'd often like better resolution
+  // we make our best effort to do this on a system-by-system basis
+#ifdef CLOCK_MONOTONIC
+  struct timespec start_time;
+#else
   time_t start_time;
+#endif
 
   // in seconds
   double elapsed_time();
@@ -27,7 +36,14 @@ public:
    * 'running' is initially false.  A timer needs to be explicitly started
    * using 'start' or 'restart'
    */
-  Timer() : running(false), start_time(0) { }
+  Timer() : running(false) {
+#ifdef CLOCK_MONOTONIC
+  start_time.tv_sec = 0;
+  start_time.tv_nsec = 0;
+#else
+  start_time = 0;
+#endif
+  }
 
   void start(const char* msg = 0);
 //  void restart(const char* msg = 0);