perf(Scope): limit propagation of $broadcast to scopes that have listeners for the event

Update $on and $destroy to maintain a count of event keys registered for each scope and its children.
$broadcast will not descend past a node that has a count of 0/undefined for the $broadcasted event key.

Closes #5341
Closes #5371

1 files changed, 29 insertions, 4 deletions

diff --git a/src/ng/rootScope.js b/src/ng/rootScope.js
index a56abc5c..1bb12869 100644
--- a/src/ng/rootScope.js
+++ b/src/ng/rootScope.js
@@ -133,6 +133,7 @@ function $RootScopeProvider(){
       this.$$asyncQueue = [];
       this.$$postDigestQueue = [];
       this.$$listeners = {};
+      this.$$listenerCount = {};
       this.$$isolateBindings = {};
     }
 
@@ -192,6 +193,7 @@ function $RootScopeProvider(){
         }
         child['this'] = child;
         child.$$listeners = {};
+        child.$$listenerCount = {};
         child.$parent = this;
         child.$$watchers = child.$$nextSibling = child.$$childHead = child.$$childTail = null;
         child.$$prevSibling = this.$$childTail;
@@ -696,6 +698,8 @@ function $RootScopeProvider(){
         this.$$destroyed = true;
         if (this === $rootScope) return;
 
+        forEach(this.$$listenerCount, bind(null, decrementListenerCount, this));
+
         if (parent.$$childHead == this) parent.$$childHead = this.$$nextSibling;
         if (parent.$$childTail == this) parent.$$childTail = this.$$prevSibling;
         if (this.$$prevSibling) this.$$prevSibling.$$nextSibling = this.$$nextSibling;
@@ -885,8 +889,18 @@ function $RootScopeProvider(){
         }
         namedListeners.push(listener);
 
+        var current = this;
+        do {
+          if (!current.$$listenerCount[name]) {
+            current.$$listenerCount[name] = 0;
+          }
+          current.$$listenerCount[name]++;
+        } while ((current = current.$parent));
+
+        var self = this;
         return function() {
           namedListeners[indexOf(namedListeners, listener)] = null;
+          decrementListenerCount(self, 1, name);
         };
       },
 
@@ -998,8 +1012,7 @@ function $RootScopeProvider(){
             listeners, i, length;
 
         //down while you can, then up and next sibling or up and next sibling until back at root
-        do {
-          current = next;
+        while ((current = next)) {
           event.currentScope = current;
           listeners = current.$$listeners[name] || [];
           for (i=0, length = listeners.length; i<length; i++) {
@@ -1021,12 +1034,14 @@ function $RootScopeProvider(){
           // Insanity Warning: scope depth-first traversal
           // yes, this code is a bit crazy, but it works and we have tests to prove it!
           // this piece should be kept in sync with the traversal in $digest
-          if (!(next = (current.$$childHead || (current !== target && current.$$nextSibling)))) {
+          // (though it differs due to having the extra check for $$listenerCount)
+          if (!(next = ((current.$$listenerCount[name] && current.$$childHead) ||
+              (current !== target && current.$$nextSibling)))) {
             while(current !== target && !(next = current.$$nextSibling)) {
               current = current.$parent;
             }
           }
-        } while ((current = next));
+        }
 
         return event;
       }
@@ -1055,6 +1070,16 @@ function $RootScopeProvider(){
       return fn;
     }
 
+    function decrementListenerCount(current, count, name) {
+      do {
+        current.$$listenerCount[name] -= count;
+
+        if (current.$$listenerCount[name] === 0) {
+          delete current.$$listenerCount[name];
+        }
+      } while ((current = current.$parent));
+    }
+
     /**
      * function used as an initial value for watchers.
      * because it's unique we can easily tell it apart from other values