Add path cache to avoid SharedPreferences jank.

The old getSharedPreferences() API had a side-effect behavior that
subsequent calls wouldn't touch disk if there was a cache hit.  Now
that we're using File as the cache key, we were generating the path
every time, which resulted in touching disk.

To bring back the old behavior, let's add yet another cache!

Bug: 26979210
Change-Id: Ib8346c6f69ae25f8f164e3b7e05bc6358de38906

1 files changed, 23 insertions, 6 deletions

diff --git a/core/java/android/app/ContextImpl.java b/core/java/android/app/ContextImpl.java
index 282707152e6a..377758ee575a 100644
--- a/core/java/android/app/ContextImpl.java
+++ b/core/java/android/app/ContextImpl.java
@@ -134,7 +134,14 @@ class ContextImpl extends Context {
     /**
      * Map from package name, to preference name, to cached preferences.
      */
-    private static ArrayMap<String, ArrayMap<File, SharedPreferencesImpl>> sSharedPrefs;
+    @GuardedBy("ContextImpl.class")
+    private static ArrayMap<String, ArrayMap<File, SharedPreferencesImpl>> sSharedPrefsCache;
+
+    /**
+     * Map from preference name to generated path.
+     */
+    @GuardedBy("ContextImpl.class")
+    private ArrayMap<String, File> mSharedPrefsPaths;
 
     final ActivityThread mMainThread;
     final LoadedApk mPackageInfo;
@@ -335,7 +342,17 @@ class ContextImpl extends Context {
             }
         }
 
-        final File file = getSharedPreferencesPath(name);
+        File file;
+        synchronized (ContextImpl.class) {
+            if (mSharedPrefsPaths == null) {
+                mSharedPrefsPaths = new ArrayMap<>();
+            }
+            file = mSharedPrefsPaths.get(name);
+            if (file == null) {
+                file = getSharedPreferencesPath(name);
+                mSharedPrefsPaths.put(name, file);
+            }
+        }
         return getSharedPreferences(file, mode);
     }
 
@@ -363,15 +380,15 @@ class ContextImpl extends Context {
     }
 
     private ArrayMap<File, SharedPreferencesImpl> getSharedPreferencesCacheLocked() {
-        if (sSharedPrefs == null) {
-            sSharedPrefs = new ArrayMap<>();
+        if (sSharedPrefsCache == null) {
+            sSharedPrefsCache = new ArrayMap<>();
         }
 
         final String packageName = getPackageName();
-        ArrayMap<File, SharedPreferencesImpl> packagePrefs = sSharedPrefs.get(packageName);
+        ArrayMap<File, SharedPreferencesImpl> packagePrefs = sSharedPrefsCache.get(packageName);
         if (packagePrefs == null) {
             packagePrefs = new ArrayMap<>();
-            sSharedPrefs.put(packageName, packagePrefs);
+            sSharedPrefsCache.put(packageName, packagePrefs);
         }
 
         return packagePrefs;