From a896b47cfe7be8fb7039fe692295419e2c5bee9e Mon Sep 17 00:00:00 2001
From: Michael Comella <michael.l.comella@gmail.com>
Date: Mon, 20 Jan 2020 18:19:10 -0800
Subject: [PATCH] For #7820: warm BrowsersCache on background thread.

In an early iteration of his patch on a beta build, I saw no improvement over
6 runs (Pixel 2):
- Before: 401.5ms
- After: 402.17ms

This may be attributed to noise in startup performance. However,
BrowsersCache disappears from profiles completely and results in
theoretical performance gains.

When using the StartupTimeline class (not landed yet), I see a 27.75ms
runtime improvement on beta builds after this patch.
---
 .../main/java/org/mozilla/fenix/FenixApplication.kt    | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/app/src/main/java/org/mozilla/fenix/FenixApplication.kt b/app/src/main/java/org/mozilla/fenix/FenixApplication.kt
index c181a8a34..80253554c 100644
--- a/app/src/main/java/org/mozilla/fenix/FenixApplication.kt
+++ b/app/src/main/java/org/mozilla/fenix/FenixApplication.kt
@@ -37,6 +37,7 @@ import org.mozilla.fenix.components.Components
 import org.mozilla.fenix.ext.settings
 import org.mozilla.fenix.session.NotificationSessionObserver
 import org.mozilla.fenix.session.VisibilityLifecycleCallback
+import org.mozilla.fenix.utils.BrowsersCache
 
 @SuppressLint("Registered")
 @Suppress("TooManyFunctions")
@@ -104,6 +105,7 @@ open class FenixApplication : LocaleAwareApplication() {
 
             setDayNightTheme()
             enableStrictMode()
+            warmBrowsersCache()
 
             // Enable the service-experiments component
             if (settings().isExperimentationEnabled && Config.channel.isReleaseOrBeta) {
@@ -260,6 +262,14 @@ open class FenixApplication : LocaleAwareApplication() {
         }
     }
 
+    private fun warmBrowsersCache() {
+        // We avoid blocking the main thread for BrowsersCache on startup by loading it on
+        // background thread.
+        GlobalScope.launch(Dispatchers.Default) {
+            BrowsersCache.all(this@FenixApplication)
+        }
+    }
+
     private fun enableStrictMode() {
         if (Config.channel.isDebug) {
             StrictMode.setThreadPolicy(