Fix lock contention in ResourcesManager

1. Scope dowm synchronized block to mAdjustedDisplays put and get
2. Use SoftReference instead of WeakReference because
   display's weak reference is cleared after getAdjustedDisplay
   returned and the cache didn't take effects previously.

fixes: 162445376
Test: ResourcesManagerPerfTest
Before:
    getDisplayMetrics_median: 3413
    getDisplayMetrics_mean: 3439
    getDisplayMetrics_min: 3364
    getDisplayMetrics_standardDeviation: 107
After:
    getDisplayMetrics_median: 3048
    getDisplayMetrics_mean: 3096
    getDisplayMetrics_min: 2999
    getDisplayMetrics_standardDeviation: 134

Change-Id: I8a5c3ba960c8231aee78b0e7fb958bf6845d5bb5

2 files changed, 38 insertions, 17 deletions

diff --git a/apct-tests/perftests/core/src/android/app/ResourcesManagerPerfTest.java b/apct-tests/perftests/core/src/android/app/ResourcesManagerPerfTest.java
index 050fecde8213..d3938f4c0926 100644
--- a/apct-tests/perftests/core/src/android/app/ResourcesManagerPerfTest.java
+++ b/apct-tests/perftests/core/src/android/app/ResourcesManagerPerfTest.java
@@ -17,7 +17,6 @@ package android.app;
 
 import android.content.Context;
 import android.content.res.Configuration;
-import android.content.res.Resources;
 import android.perftests.utils.BenchmarkState;
 import android.perftests.utils.PerfStatusReporter;
 import android.view.Display;
@@ -136,4 +135,22 @@ public class ResourcesManagerPerfTest {
             }
         }
     }
+
+    @Test
+    public void getDisplayMetrics() {
+        ResourcesManager resourcesManager = ResourcesManager.getInstance();
+
+        final BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        while (state.keepRunning()) {
+            state.pauseTiming();
+            // Invalidate cache.
+            resourcesManager.applyConfigurationToResourcesLocked(
+                    resourcesManager.getConfiguration(), null);
+            state.resumeTiming();
+
+            // Invoke twice for testing cache.
+            resourcesManager.getDisplayMetrics();
+            resourcesManager.getDisplayMetrics();
+        }
+    }
 }
diff --git a/core/java/android/app/ResourcesManager.java b/core/java/android/app/ResourcesManager.java
index 7cd3fcad177b..9e4ab33c6aa0 100644
--- a/core/java/android/app/ResourcesManager.java
+++ b/core/java/android/app/ResourcesManager.java
@@ -54,6 +54,7 @@ import java.io.IOException;
 import java.io.PrintWriter;
 import java.lang.ref.Reference;
 import java.lang.ref.ReferenceQueue;
+import java.lang.ref.SoftReference;
 import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -245,7 +246,7 @@ public class ResourcesManager {
     /**
      * A cache of DisplayId, DisplayAdjustments to Display.
      */
-    private final ArrayMap<Pair<Integer, DisplayAdjustments>, WeakReference<Display>>
+    private final ArrayMap<Pair<Integer, DisplayAdjustments>, SoftReference<Display>>
             mAdjustedDisplays = new ArrayMap<>();
 
     /**
@@ -373,25 +374,28 @@ public class ResourcesManager {
                 ? new DisplayAdjustments(displayAdjustments) : new DisplayAdjustments();
         final Pair<Integer, DisplayAdjustments> key =
                 Pair.create(displayId, displayAdjustmentsCopy);
+        SoftReference<Display> sd;
         synchronized (this) {
-            WeakReference<Display> wd = mAdjustedDisplays.get(key);
-            if (wd != null) {
-                final Display display = wd.get();
-                if (display != null) {
-                    return display;
-                }
-            }
-            final DisplayManagerGlobal dm = DisplayManagerGlobal.getInstance();
-            if (dm == null) {
-                // may be null early in system startup
-                return null;
-            }
-            final Display display = dm.getCompatibleDisplay(displayId, key.second);
+            sd = mAdjustedDisplays.get(key);
+        }
+        if (sd != null) {
+            final Display display = sd.get();
             if (display != null) {
-                mAdjustedDisplays.put(key, new WeakReference<>(display));
+                return display;
+            }
+        }
+        final DisplayManagerGlobal dm = DisplayManagerGlobal.getInstance();
+        if (dm == null) {
+            // may be null early in system startup
+            return null;
+        }
+        final Display display = dm.getCompatibleDisplay(displayId, key.second);
+        if (display != null) {
+            synchronized (this) {
+                mAdjustedDisplays.put(key, new SoftReference<>(display));
             }
-            return display;
         }
+        return display;
     }
 
     /**