From b8dd2652982f165a6f206b16b189baf78602ffcf Mon Sep 17 00:00:00 2001
From: Tim Murray <timmurray@google.com>
Date: Fri, 23 Jun 2023 16:27:43 -0700
Subject: SharedPreferences: replace per-load threads with single thread

Switch to a shared executor instead of explicit threads for
SharedPreferences loads in order to reduce mmap_sem contention from
thread creation spam.

Test: atest android.content.cts.SharedPreferencesTest
Bug: 289006197
Change-Id: Ieed7bdaa3f08c3fe9121b157d8bdb29b013f4b83
---
 core/java/android/app/SharedPreferencesImpl.java | 28 +++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/core/java/android/app/SharedPreferencesImpl.java b/core/java/android/app/SharedPreferencesImpl.java
index 1ebf56550e03..a87187b8affb 100644
--- a/core/java/android/app/SharedPreferencesImpl.java
+++ b/core/java/android/app/SharedPreferencesImpl.java
@@ -55,6 +55,11 @@ import java.util.Map;
 import java.util.Set;
 import java.util.WeakHashMap;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
 
 final class SharedPreferencesImpl implements SharedPreferences {
     private static final String TAG = "SharedPreferencesImpl";
@@ -119,6 +124,10 @@ final class SharedPreferencesImpl implements SharedPreferences {
     private final ExponentiallyBucketedHistogram mSyncTimes = new ExponentiallyBucketedHistogram(16);
     private int mNumSync = 0;
 
+    private static final ThreadPoolExecutor sLoadExecutor = new ThreadPoolExecutor(0, 1, 10L,
+            TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(),
+            new SharedPreferencesThreadFactory());
+
     @UnsupportedAppUsage
     SharedPreferencesImpl(File file, int mode) {
         mFile = file;
@@ -135,11 +144,10 @@ final class SharedPreferencesImpl implements SharedPreferences {
         synchronized (mLock) {
             mLoaded = false;
         }
-        new Thread("SharedPreferencesImpl-load") {
-            public void run() {
-                loadFromDisk();
-            }
-        }.start();
+
+        sLoadExecutor.execute(() -> {
+            loadFromDisk();
+        });
     }
 
     private void loadFromDisk() {
@@ -874,4 +882,14 @@ final class SharedPreferencesImpl implements SharedPreferences {
         }
         mcr.setDiskWriteResult(false, false);
     }
+
+
+    private static final class SharedPreferencesThreadFactory implements ThreadFactory {
+        @Override
+        public Thread newThread(Runnable runnable) {
+            Thread thread = Executors.defaultThreadFactory().newThread(runnable);
+            thread.setName("SharedPreferences");
+            return thread;
+        }
+    }
 }
-- 
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