Add sequence ID to emit calls to prevent race

lib/page.js

@@ -26,6 +26,7 @@ module.exports = exports = function(options) {
       context = Contextify.createContext({}),
       window = context.getGlobal(),
       _id = windowId++,
+      requestId = 0,
       $;
 
   _.extend(window, {
@@ -41,7 +42,14 @@ module.exports = exports = function(options) {
     emit: function(after) {
       function checkComplete() {
         if (isComplete()) {
-          setImmediate(emit);
+          var associatedRequestId = requestId;
+          setImmediate(function() {
+            // Avoid a race condtion where pooled requests may come in while we still have
+            // pending emit calls. This will generally only happen for very chatty emit callers.
+            if (requestId === associatedRequestId) {
+              emit();
+            }
+          });
         }
       }
       function isComplete() {
@@ -242,6 +250,7 @@ module.exports = exports = function(options) {
     },
 
     navigate: function(path, _callback) {
+      requestId++;
       window._start = start = process.hrtime();
       callback = _callback;
       dom.location(window, protocol + '//' + host + path, redirect);