From c8593984523978da380181cd15c3c496b9a5a65d Mon Sep 17 00:00:00 2001
From: Jared Duke <jdduke@google.com>
Date: Wed, 2 Mar 2022 13:10:19 -0800
Subject: [PATCH] Avoid unnecessary Clock GC churn

Avoid recreating SimpleDateFormat and DateTimePatternGenerator objects
for each clock update. While the allocation sizes are relatively small,
they are continuous, and potentially frequent when seconds are shown.

Test: atest SystemUITests:StatusBarTest + visual inspection
Bug: 204187068
Change-Id: Ia267c6df44002328c6c32115326dc092ee89393f
---
 .../systemui/statusbar/policy/Clock.java      | 34 +++++++++++--------
 1 file changed, 20 insertions(+), 14 deletions(-)

diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/policy/Clock.java b/packages/SystemUI/src/com/android/systemui/statusbar/policy/Clock.java
index 562816fbe21fc..9e1e87b9856f3 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/policy/Clock.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/policy/Clock.java
@@ -88,10 +88,11 @@ public class Clock extends TextView implements
     private boolean mAttached;
     private boolean mScreenReceiverRegistered;
     private Calendar mCalendar;
-    private String mClockFormatString;
+    private String mContentDescriptionFormatString;
     private SimpleDateFormat mClockFormat;
     private SimpleDateFormat mContentDescriptionFormat;
     private Locale mLocale;
+    private DateTimePatternGenerator mDateTimePatternGenerator;
 
     private static final int AM_PM_STYLE_NORMAL  = 0;
     private static final int AM_PM_STYLE_SMALL   = 1;
@@ -196,7 +197,8 @@ public class Clock extends TextView implements
 
         // The time zone may have changed while the receiver wasn't registered, so update the Time
         mCalendar = Calendar.getInstance(TimeZone.getDefault());
-        mClockFormatString = "";
+        mContentDescriptionFormatString = "";
+        mDateTimePatternGenerator = null;
 
         // Make sure we update to the current time
         updateClock();
@@ -247,7 +249,9 @@ public class Clock extends TextView implements
                 handler.post(() -> {
                     if (!newLocale.equals(mLocale)) {
                         mLocale = newLocale;
-                        mClockFormatString = ""; // force refresh
+                         // Force refresh of dependent variables.
+                        mContentDescriptionFormatString = "";
+                        mDateTimePatternGenerator = null;
                     }
                 });
             }
@@ -367,17 +371,22 @@ public class Clock extends TextView implements
     private final CharSequence getSmallTime() {
         Context context = getContext();
         boolean is24 = DateFormat.is24HourFormat(context, mCurrentUserId);
-        DateTimePatternGenerator dtpg = DateTimePatternGenerator.getInstance(
+        if (mDateTimePatternGenerator == null) {
+            // Despite its name, getInstance creates a cloned instance, so reuse the generator to
+            // avoid unnecessary churn.
+            mDateTimePatternGenerator = DateTimePatternGenerator.getInstance(
                 context.getResources().getConfiguration().locale);
+        }
 
         final char MAGIC1 = '\uEF00';
         final char MAGIC2 = '\uEF01';
 
-        SimpleDateFormat sdf;
-        String format = mShowSeconds
-                ? is24 ? dtpg.getBestPattern("Hms") : dtpg.getBestPattern("hms")
-                : is24 ? dtpg.getBestPattern("Hm") : dtpg.getBestPattern("hm");
-        if (!format.equals(mClockFormatString)) {
+        final String formatSkeleton = mShowSeconds
+                ? is24 ? "Hms" : "hms"
+                : is24 ? "Hm" : "hm";
+        String format = mDateTimePatternGenerator.getBestPattern(formatSkeleton);
+        if (!format.equals(mContentDescriptionFormatString)) {
+            mContentDescriptionFormatString = format;
             mContentDescriptionFormat = new SimpleDateFormat(format);
             /*
              * Search for an unquoted "a" in the format string, so we can
@@ -409,12 +418,9 @@ public class Clock extends TextView implements
                         + "a" + MAGIC2 + format.substring(b + 1);
                 }
             }
-            mClockFormat = sdf = new SimpleDateFormat(format);
-            mClockFormatString = format;
-        } else {
-            sdf = mClockFormat;
+            mClockFormat = new SimpleDateFormat(format);
         }
-        String result = sdf.format(mCalendar.getTime());
+        String result = mClockFormat.format(mCalendar.getTime());
 
         if (mAmPmStyle != AM_PM_STYLE_NORMAL) {
             int magic1 = result.indexOf(MAGIC1);