From fc9af34b9d0815a27077d29c5aea360a3e73ae57 Mon Sep 17 00:00:00 2001
From: Selim Cinek <cinek@google.com>
Date: Fri, 5 May 2017 14:45:11 -0700
Subject: [PATCH] Fixed a concurrent modification crash

Test: runtest -x packages/SystemUI/tests/src/com/android/systemui/settings/CurrentUserTrackerTest.java
Change-Id: I23261843b7366d3a66a795a41c61b7661f7ca3a6
Fixes: 38006784
---
 .../systemui/settings/CurrentUserTracker.java | 23 +++++--
 .../settings/CurrentUserTrackerTest.java      | 65 +++++++++++++++++++
 2 files changed, 83 insertions(+), 5 deletions(-)
 create mode 100644 packages/SystemUI/tests/src/com/android/systemui/settings/CurrentUserTrackerTest.java

diff --git a/packages/SystemUI/src/com/android/systemui/settings/CurrentUserTracker.java b/packages/SystemUI/src/com/android/systemui/settings/CurrentUserTracker.java
index 005206fcd14c5..0b89dc1070e12 100644
--- a/packages/SystemUI/src/com/android/systemui/settings/CurrentUserTracker.java
+++ b/packages/SystemUI/src/com/android/systemui/settings/CurrentUserTracker.java
@@ -22,6 +22,8 @@ import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
 
+import com.android.internal.annotations.VisibleForTesting;
+
 import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Consumer;
@@ -32,7 +34,12 @@ public abstract class CurrentUserTracker {
     private Consumer<Integer> mCallback = this::onUserSwitched;
 
     public CurrentUserTracker(Context context) {
-        mUserReceiver = UserReceiver.getInstance(context);
+        this(UserReceiver.getInstance(context));
+    }
+
+    @VisibleForTesting
+    CurrentUserTracker(UserReceiver receiver) {
+        mUserReceiver = receiver;
     }
 
     public int getCurrentUserId() {
@@ -49,7 +56,8 @@ public abstract class CurrentUserTracker {
 
     public abstract void onUserSwitched(int newUserId);
 
-    private static class UserReceiver extends BroadcastReceiver {
+    @VisibleForTesting
+    static class UserReceiver extends BroadcastReceiver {
         private static UserReceiver sInstance;
 
         private Context mAppContext;
@@ -58,7 +66,8 @@ public abstract class CurrentUserTracker {
 
         private List<Consumer<Integer>> mCallbacks = new ArrayList<>();
 
-        private UserReceiver(Context context) {
+        @VisibleForTesting
+        UserReceiver(Context context) {
             mAppContext = context.getApplicationContext();
         }
 
@@ -105,8 +114,12 @@ public abstract class CurrentUserTracker {
         private void notifyUserSwitched(int newUserId) {
             if (mCurrentUserId != newUserId) {
                 mCurrentUserId = newUserId;
-                for (Consumer<Integer> consumer : mCallbacks) {
-                    consumer.accept(newUserId);
+                List<Consumer<Integer>> callbacks = new ArrayList<>(mCallbacks);
+                for (Consumer<Integer> consumer : callbacks) {
+                    // Accepting may modify this list
+                    if (mCallbacks.contains(consumer)) {
+                        consumer.accept(newUserId);
+                    }
                 }
             }
         }
diff --git a/packages/SystemUI/tests/src/com/android/systemui/settings/CurrentUserTrackerTest.java b/packages/SystemUI/tests/src/com/android/systemui/settings/CurrentUserTrackerTest.java
new file mode 100644
index 0000000000000..9e15a054d22fc
--- /dev/null
+++ b/packages/SystemUI/tests/src/com/android/systemui/settings/CurrentUserTrackerTest.java
@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+package com.android.systemui.settings;
+
+import android.content.Intent;
+
+import com.android.systemui.SysuiTestCase;
+
+import org.junit.Before;
+import org.junit.Test;
+
+/**
+ * Testing functionality of the current user tracker
+ */
+public class CurrentUserTrackerTest extends SysuiTestCase {
+
+    private CurrentUserTracker mTracker;
+    private CurrentUserTracker.UserReceiver mReceiver;
+
+    @Before
+    public void setUp() {
+        mReceiver = new CurrentUserTracker.UserReceiver(getContext());
+        mTracker = new CurrentUserTracker(mReceiver) {
+            @Override
+            public void onUserSwitched(int newUserId) {
+                stopTracking();
+            }
+        };
+    }
+
+    @Test
+    public void testBroadCastDoesntCrashOnConcurrentModification() {
+        mTracker.startTracking();
+        CurrentUserTracker secondTracker = new CurrentUserTracker(mReceiver) {
+            @Override
+            public void onUserSwitched(int newUserId) {
+                stopTracking();
+            }
+        };
+        secondTracker.startTracking();
+        triggerUserSwitch();
+    }
+    /**
+     * Simulates a user switch event.
+     */
+    private void triggerUserSwitch() {
+        Intent intent = new Intent(Intent.ACTION_USER_SWITCHED);
+        intent.putExtra(Intent.EXTRA_USER_HANDLE, 1);
+        mReceiver.onReceive(getContext(), intent);
+    }
+}