fgdata/Nasal: avoid performance drop after sim reset/relocate

"/sim/signals/fdm-initialized" triggers _every_ time the FDM is reset,
so for every sim reset/relocate.
We need to uninstall the listeners after its first execution, or guard
certain parts of the initialization, to avoid starting multiple
"timer/update loops", or installing multiple property listeners.
Repeating "sim reset" often enough would eventually completely block/
overload the system.

Nasal/failures.nas

@@ -177,12 +177,12 @@ var setAllMCBF = func(mcbf) {
     }
 }
 
-
 # Initialization, called once Nasal and the FDM are loaded properly.
-_setlistener("/sim/signals/fdm-initialized", func {
+var fdm_init_listener = _setlistener("/sim/signals/fdm-initialized-once", func {
+    removelistener(fdm_init_listener); # uninstall, so we're only called once
     srand();
 
-    # Engines are added dynamically because there may be an arbritary number
+    # Engines are added dynamically because there may be an arbitrary number
     var i = 1;
     foreach (var e; props.globals.getNode("/engines").getChildren("engine")) {
         breakHash[e.getPath()] = { type: type.MTBF, failure: fail.ENGINE, desc : "Engine " ~ i };

Nasal/fuel.nas

@@ -68,8 +68,14 @@ var tanks = [];
 var engines = [];
 var fuel_freeze = nil;
 
+var freeze_fuel_listener = nil;
+var initialized = 0;
+
 _setlistener("/sim/signals/fdm-initialized", func {
-	setlistener("/sim/freeze/fuel", func(n) { fuel_freeze = n.getBoolValue() }, 1);
+	if (freeze_fuel_listener == nil)
+	{
+		freeze_fuel_listener = setlistener("/sim/freeze/fuel", func(n) { fuel_freeze = n.getBoolValue() }, 1);
+	}
 
 	# Fuel sub-system is only used by YASim. Other FDMs (e.g. JSBSim)
 	# handle fuel themselves.
@@ -81,6 +87,11 @@ _setlistener("/sim/signals/fdm-initialized", func {
 		e.getNode("out-of-fuel", 1).setBoolValue(0);
 	}
 
+	# do the following stuff once only
+	if (initialized)
+		return;
+	initialized = 1;
+
 	foreach (var t; props.globals.getNode("/consumables/fuel", 1).getChildren("tank")) {
 		if (!t.getAttribute("children"))
 			continue;           # skip native_fdm.cxx generated zombie tanks

Nasal/glide_slope_tunnel.nas

@@ -87,7 +87,8 @@ var loop = func(id) {
 
 var loopid = 0;
 
-_setlistener("/sim/signals/fdm-initialized", func {
+var fdm_init_listener = _setlistener("/sim/signals/fdm-initialized", func {
+	removelistener(fdm_init_listener); # uninstall, so we're only called once
 	# remove top bar unless otherwise specified
 	var top = props.globals.initNode("/sim/model/geometry/square/top", 1, "BOOL");
 

Nasal/redout.nas

@@ -114,8 +114,9 @@ var check_params = func() {
   }
 }
 
-_setlistener("/sim/signals/fdm-initialized",
+var fdm_init_listener = _setlistener("/sim/signals/fdm-initialized",
   func {
+    removelistener(fdm_init_listener); # uninstall, so we're only called once
     fdm = getprop("/sim/flight-model");
     running_redout = getprop("/sim/rendering/redout/enabled");
     running_compression = getprop("/sim/rendering/headshake/enabled");

Nasal/screen.nas

@@ -435,7 +435,8 @@ _setlistener("/sim/signals/nasal-dir-initialized", func {
 # --prop:display=position/              ... adds all properties under /position/  (ends with slash!)
 # --prop:display=position/,orientation/ ... separate multiple properties with comma
 #
-_setlistener("/sim/signals/fdm-initialized", func {
+var fdm_init_listener = _setlistener("/sim/signals/fdm-initialized", func {
+	removelistener(fdm_init_listener); # uninstall, so we're only called once
 	foreach (var n; props.globals.getChildren("display")) {
 		foreach (var p; split(",", n.getValue())) {
 			if (!size(p))

Nasal/view.nas

@@ -655,7 +655,8 @@ _setlistener("/sim/signals/nasal-dir-initialized", func {
 });
 
 
-_setlistener("/sim/signals/fdm-initialized", func {
+var fdm_init_listener = _setlistener("/sim/signals/fdm-initialized", func {
+	removelistener(fdm_init_listener); # uninstall, so we're only called once
 	var zoffset = nil;
 	foreach (var v; views) {
 		var index = v.getIndex();