There was an integer overflow in the way elapsed_time_ms. Because the

SGTimeStamp "-" operator returns it's result in usec's, there is an upper bound of 37.8 minutes on the maximum difference this operator can reliably report
before the math overflows.  I change the global "int elapsed_time_ms" variable
to a "double sim_time_ms" and restructured how the value is calculated.
----
The practical result of the overflow bug is that a large negative dt was
passed to the event manager and the end effect was that no events would
be run until their counters caught up ... in another 37.8 minutes or so.

diff --git a/src/Main/fg_props.cxx b/src/Main/fg_props.cxx
index 33f9e2028fb49fc911a787055a28091c770a7704..152dbae1ec7dcf6dc6ef597f755164e4e6a77de8 100644 (file)
--- a/src/Main/fg_props.cxx
+++ b/src/Main/fg_props.cxx
@@ -264,10 +264,10 @@ setAircraftDir (const char * dir)
 /**
  * Return the number of milliseconds elapsed since simulation started.
  */
-static long
+static double
 getElapsedTime_ms ()
 {
-  return globals->get_elapsed_time_ms();
+  return globals->get_sim_time_ms();
 }
 
 

diff --git a/src/Main/globals.cxx b/src/Main/globals.cxx
index b03f7f0a8dc4dd731c20bb4a79a411a820d58f36..44ba968c4b386d5d33ece7c6d6261b1efb113548 100644 (file)
--- a/src/Main/globals.cxx
+++ b/src/Main/globals.cxx
@@ -42,7 +42,7 @@ FGGlobals *globals;
 
 // Constructor
 FGGlobals::FGGlobals() :
-    elapsed_time_ms(0L),
+    sim_time_ms(0.0),
 #if defined(FX) && defined(XMESA)
     fullscreen( true ),
 #endif

diff --git a/src/Main/globals.hxx b/src/Main/globals.hxx
index 67bea6200022342ce39218fe2a973552a870e685..ee8036c88f32adda22f098499244ed4ed220957a 100644 (file)
--- a/src/Main/globals.hxx
+++ b/src/Main/globals.hxx
@@ -80,7 +80,7 @@ class FGGlobals
 private:
 
     // Number of milliseconds elapsed since the start of the program.
-    long elapsed_time_ms;
+    double sim_time_ms;
 
     // Root of FlightGear data tree
     string fg_root;
@@ -174,8 +174,9 @@ public:
     FGGlobals();
     ~FGGlobals();
 
-    inline long get_elapsed_time_ms () const { return elapsed_time_ms; }
-    inline void set_elapsed_time_ms (long t) { elapsed_time_ms = t; }
+    inline double get_sim_time_ms () const { return sim_time_ms; }
+    inline void inc_sim_time_ms (double dt) { sim_time_ms += dt; }
+    inline void set_sim_time_ms (double t) { sim_time_ms = t; }
 
     inline const string &get_fg_root () const { return fg_root; }
     inline void set_fg_root (const string &root) { fg_root = root; }

diff --git a/src/Main/logger.cxx b/src/Main/logger.cxx
index cef1a46e163983bfa4ff51459e88ae2bee3b9359..7958300bbe0b93a53091a6384d6c03f6d1dd1f60 100644 (file)
--- a/src/Main/logger.cxx
+++ b/src/Main/logger.cxx
@@ -79,11 +79,11 @@ FGLogger::unbind ()
 void
 FGLogger::update (int dt)
 {
-  long elapsed_ms = globals->get_elapsed_time_ms();
+  double sim_time_ms = globals->get_sim_time_ms();
   for (unsigned int i = 0; i < _logs.size(); i++) {
-    if ((elapsed_ms - _logs[i].last_time_ms) >= _logs[i].interval_ms) {
-      _logs[i].last_time_ms = elapsed_ms;
-      (*_logs[i].output) << globals->get_elapsed_time_ms();
+    if ((sim_time_ms - _logs[i].last_time_ms) >= _logs[i].interval_ms) {
+      _logs[i].last_time_ms = sim_time_ms;
+      (*_logs[i].output) << globals->get_sim_time_ms();
       for (unsigned int j = 0; j < _logs[i].nodes.size(); j++) {
        (*_logs[i].output) << _logs[i].delimiter
                           << _logs[i].nodes[j]->getStringValue();
@@ -102,7 +102,7 @@ FGLogger::update (int dt)
 FGLogger::Log::Log ()
   : output(0),
     interval_ms(0),
-    last_time_ms(-999999L),
+    last_time_ms(-999999.0),
     delimiter(',')
 {
 }

diff --git a/src/Main/logger.hxx b/src/Main/logger.hxx
index fe2bc7948db8e33704a40d2a7137f42d0fa04c78..2929c421c6a15a9ff4394219b04edff67303cfd3 100644 (file)
--- a/src/Main/logger.hxx
+++ b/src/Main/logger.hxx
@@ -57,7 +57,7 @@ private:
     vector<SGPropertyNode *> nodes;
     ostream * output;
     long interval_ms;
-    long last_time_ms;
+    double last_time_ms;
     char delimiter;
   };
 

diff --git a/src/Main/main.cxx b/src/Main/main.cxx
index 94909df9c1f64abf97f84c69bc7f52f6965879b8..5e758d7d68deb31c48b4c930a103893909876242 100644 (file)
--- a/src/Main/main.cxx
+++ b/src/Main/main.cxx
@@ -241,7 +241,7 @@ ssgSimpleState *default_state;
 ssgSimpleState *hud_and_panel;
 ssgSimpleState *menus;
 
-SGTimeStamp start_time_stamp;
+SGTimeStamp last_time_stamp;
 SGTimeStamp current_time_stamp;
 
 void fgBuildRenderStates( void ) {
@@ -393,10 +393,11 @@ void trRenderFrame( void ) {
 // Update all Visuals (redraws anything graphics related)
 void fgRenderFrame( void ) {
   
-    static long old_elapsed_ms = 0;
-
-    int dt_ms = int(globals->get_elapsed_time_ms() - old_elapsed_ms);
-    old_elapsed_ms = globals->get_elapsed_time_ms();
+    // Update the elapsed time.
+    current_time_stamp.stamp();
+    int dt_ms = (current_time_stamp - last_time_stamp) / 1000L;
+    globals->inc_sim_time_ms( dt_ms );
+    last_time_stamp = current_time_stamp;
 
     // Process/manage pending events
     global_events.update( dt_ms );
@@ -440,17 +441,13 @@ void fgRenderFrame( void ) {
        if ( fgGetBool("/sim/startup/splash-screen") ) {
            fgSplashUpdate(0.0);
        }
-       start_time_stamp.stamp(); // Keep resetting the start time
+        // Keep resetting sim time while the sim is initializing
+       globals->set_sim_time_ms( 0.0 );
     } else {
        // idle_state is now 1000 meaning we've finished all our
        // initializations and are running the main loop, so this will
        // now work without seg faulting the system.
 
-        // Update the elapsed time.
-        current_time_stamp.stamp();
-       globals->set_elapsed_time_ms( (current_time_stamp - start_time_stamp)
-                                      / 1000L );
-
        // calculate our current position in cartesian space
        scenery.set_center( scenery.get_next_center() );