From 65b51b8d9155f72fd8eb61662d5a4d0eccbdbfd2 Mon Sep 17 00:00:00 2001
From: Torsten Dreyer <torsten@t3r.de>
Date: Wed, 26 Oct 2016 11:02:24 +0200
Subject: [PATCH] Limit the update rate of the property change websocket

Of fast systems with 60fps sending many properties to web clients
may overrun the rendering capabilities of the browser. At some point
the web socket client halts the simulation by throtteling the network
connection.

Update rate is settable at startup setting to a double value
/sim/http/property-websocket/update-interval-secs
(default: 0.05 aka 20Hz)
---
 src/Network/http/PropertyChangeWebsocket.cxx | 16 ++++++++++++++--
 src/Network/http/PropertyChangeWebsocket.hxx |  2 ++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/Network/http/PropertyChangeWebsocket.cxx b/src/Network/http/PropertyChangeWebsocket.cxx
index c1c23b516..0c70061f1 100644
--- a/src/Network/http/PropertyChangeWebsocket.cxx
+++ b/src/Network/http/PropertyChangeWebsocket.cxx
@@ -118,7 +118,10 @@ static void handleExecCommand(cJSON* json)
 }
   
 PropertyChangeWebsocket::PropertyChangeWebsocket(PropertyChangeObserver * propertyChangeObserver)
-    : id(++nextid), _propertyChangeObserver(propertyChangeObserver)
+    : id(++nextid),
+      _propertyChangeObserver(propertyChangeObserver),
+      _minTriggerInterval(fgGetDouble("/sim/http/property-websocket/update-interval-secs", 0.05)), // default 20Hz
+      _lastTrigger(-1000)
 {
 }
 
@@ -206,12 +209,21 @@ void PropertyChangeWebsocket::handleRequest(const HTTPRequest & request, Websock
 
 void PropertyChangeWebsocket::poll(WebsocketWriter & writer)
 {
+  double now = fgGetDouble("/sim/time/elapsed-sec");
+
+  if( _minTriggerInterval > .0 ) {
+    if( now - _lastTrigger <= _minTriggerInterval )
+      return;
+
+    _lastTrigger = now;
+  }
+
   for (WatchedNodesList::iterator it = _watchedNodes.begin(); it != _watchedNodes.end(); ++it) {
     SGPropertyNode_ptr node = *it;
 
     string newValue;
     if (_propertyChangeObserver->isChangedValue(node)) {
-      string out = JSON::toJsonString( false, node, 0, fgGetDouble("/sim/time/elapsed-sec") );
+      string out = JSON::toJsonString( false, node, 0, now );
       SG_LOG(SG_NETWORK, SG_DEBUG, "PropertyChangeWebsocket::poll() new Value for " << node->getPath(true) << " '" << node->getStringValue() << "' #" << id << ": " << out );
       writer.writeText( out );
     }
diff --git a/src/Network/http/PropertyChangeWebsocket.hxx b/src/Network/http/PropertyChangeWebsocket.hxx
index 3f5af11f5..2409961ca 100644
--- a/src/Network/http/PropertyChangeWebsocket.hxx
+++ b/src/Network/http/PropertyChangeWebsocket.hxx
@@ -51,6 +51,8 @@ private:
   };
 
   WatchedNodesList _watchedNodes;
+  double _minTriggerInterval;
+  double _lastTrigger;
 };
 
 }