From c8312dd5ae0e94629bb6e69f420f3654ff42e94a Mon Sep 17 00:00:00 2001
From: Luke Barnard <luke@matrix.org>
Date: Wed, 28 Mar 2018 10:25:28 +0100
Subject: [PATCH] Use a less fragile API to track page change performance

---
 src/Analytics.js                        | 23 +++-------------
 src/components/structures/MatrixChat.js | 35 ++++++++++++++++++++++---
 2 files changed, 35 insertions(+), 23 deletions(-)

diff --git a/src/Analytics.js b/src/Analytics.js
index ab47d30c1d..bb9f900145 100644
--- a/src/Analytics.js
+++ b/src/Analytics.js
@@ -148,24 +148,7 @@ class Analytics {
         return true;
     }
 
-    startPageChangeTimer() {
-        performance.clearMarks('riot_page_change_start');
-        performance.mark('riot_page_change_start');
-    }
-
-    stopPageChangeTimer() {
-        performance.mark('riot_page_change_stop');
-        performance.measure(
-            'riot_page_change_delta',
-            'riot_page_change_start',
-            'riot_page_change_stop',
-        );
-
-        const measurement = performance.getEntriesByName('riot_page_change_delta').pop();
-        this.generationTimeMs = measurement.duration;
-    }
-
-    trackPageChange() {
+    trackPageChange(generationTimeMs) {
         if (this.disabled) return;
         if (this.firstPage) {
             // De-duplicate first page
@@ -174,8 +157,8 @@ class Analytics {
             return;
         }
         this._paq.push(['setCustomUrl', getRedactedUrl()]);
-        if (typeof this.generationTimeMs === 'number') {
-            this._paq.push(['setGenerationTimeMs', this.generationTimeMs]);
+        if (typeof generationTimeMs === 'number') {
+            this._paq.push(['setGenerationTimeMs', generationTimeMs]);
         }
         this._paq.push(['trackPageView']);
     }
diff --git a/src/components/structures/MatrixChat.js b/src/components/structures/MatrixChat.js
index a898808141..2c38e3d26e 100644
--- a/src/components/structures/MatrixChat.js
+++ b/src/components/structures/MatrixChat.js
@@ -370,14 +370,14 @@ export default React.createClass({
 
     componentWillUpdate: function(props, state) {
         if (this.shouldTrackPageChange(this.state, state)) {
-            Analytics.startPageChangeTimer();
+            this.startPageChangeTimer();
         }
     },
 
     componentDidUpdate: function(prevProps, prevState) {
         if (this.shouldTrackPageChange(prevState, this.state)) {
-            Analytics.stopPageChangeTimer();
-            Analytics.trackPageChange();
+            const durationMs = this.stopPageChangeTimer();
+            Analytics.trackPageChange(durationMs);
         }
         if (this.focusComposer) {
             dis.dispatch({action: 'focus_composer'});
@@ -385,6 +385,35 @@ export default React.createClass({
         }
     },
 
+    startPageChangeTimer() {
+        // This shouldn't happen because componentWillUpdate and componentDidUpdate
+        // are used.
+        if (this._pageChanging) {
+            console.warn('MatrixChat.startPageChangeTimer: timer already started');
+            return;
+        }
+        this._pageChanging = true;
+        performance.mark('riot_MatrixChat_page_change_start');
+    },
+
+    stopPageChangeTimer() {
+        if (!this._pageChanging) {
+            console.warn('MatrixChat.stopPageChangeTimer: timer not started');
+            return;
+        }
+        this._pageChanging = false;
+        performance.mark('riot_MatrixChat_page_change_stop');
+        performance.measure(
+            'riot_MatrixChat_page_change_delta',
+            'riot_MatrixChat_page_change_start',
+            'riot_MatrixChat_page_change_stop',
+        );
+        performance.clearMarks('riot_MatrixChat_page_change_start');
+        performance.clearMarks('riot_MatrixChat_page_change_stop');
+        const measurement = performance.getEntriesByName('riot_MatrixChat_page_change_delta').pop();
+        return measurement.duration;
+    },
+
     shouldTrackPageChange(prevState, state) {
         return prevState.currentRoomId !== state.currentRoomId ||
             prevState.view !== state.view ||