Add ListenerSet and use in places which currently copy-on-iterate.

Test: atest ListenerSetTest
Change-Id: Ic1320b4f6c424322451f7def11346865bf878f99

packages/SystemUI/src/com/android/systemui/statusbar/phone/KeyguardBouncer.java

@@ -44,6 +44,7 @@ import com.android.systemui.dagger.qualifiers.RootView;
 import com.android.systemui.keyguard.DismissCallbackRegistry;
 import com.android.systemui.shared.system.SysUiStatsLog;
 import com.android.systemui.statusbar.policy.KeyguardStateController;
+import com.android.systemui.util.ListenerSet;
 
 import java.io.PrintWriter;
 import java.util.ArrayList;
@@ -83,11 +84,11 @@ public class KeyguardBouncer {
     private final Runnable mRemoveViewRunnable = this::removeView;
     private final KeyguardBypassController mKeyguardBypassController;
     private KeyguardHostViewController mKeyguardViewController;
-    private final List<KeyguardResetCallback> mResetCallbacks = new ArrayList<>();
+    private final ListenerSet<KeyguardResetCallback> mResetCallbacks = new ListenerSet<>();
     private final Runnable mResetRunnable = ()-> {
         if (mKeyguardViewController != null) {
             mKeyguardViewController.resetSecurityContainer();
-            for (KeyguardResetCallback callback : new ArrayList<>(mResetCallbacks)) {
+            for (KeyguardResetCallback callback : mResetCallbacks) {
                 callback.onKeyguardReset();
             }
         }
@@ -602,7 +603,7 @@ public class KeyguardBouncer {
     }
 
     public void addKeyguardResetCallback(KeyguardResetCallback callback) {
-        mResetCallbacks.add(callback);
+        mResetCallbacks.addIfAbsent(callback);
     }
 
     public void removeKeyguardResetCallback(KeyguardResetCallback callback) {

packages/SystemUI/src/com/android/systemui/statusbar/policy/HeadsUpManager.java

@@ -38,11 +38,10 @@ import com.android.systemui.R;
 import com.android.systemui.statusbar.AlertingNotificationManager;
 import com.android.systemui.statusbar.notification.collection.NotificationEntry;
 import com.android.systemui.statusbar.notification.row.NotificationRowContentBinder.InflationFlag;
+import com.android.systemui.util.ListenerSet;
 
 import java.io.FileDescriptor;
 import java.io.PrintWriter;
-import java.util.ArrayList;
-import java.util.HashSet;
 
 /**
  * A manager which handles heads up notifications which is a special mode where
@@ -52,7 +51,7 @@ public abstract class HeadsUpManager extends AlertingNotificationManager {
     private static final String TAG = "HeadsUpManager";
     private static final String SETTING_HEADS_UP_SNOOZE_LENGTH_MS = "heads_up_snooze_length_ms";
 
-    protected final HashSet<OnHeadsUpChangedListener> mListeners = new HashSet<>();
+    protected final ListenerSet<OnHeadsUpChangedListener> mListeners = new ListenerSet<>();
 
     protected final Context mContext;
 
@@ -118,7 +117,7 @@ public abstract class HeadsUpManager extends AlertingNotificationManager {
      * Adds an OnHeadUpChangedListener to observe events.
      */
     public void addListener(@NonNull OnHeadsUpChangedListener listener) {
-        mListeners.add(listener);
+        mListeners.addIfAbsent(listener);
     }
 
     /**
@@ -158,7 +157,7 @@ public abstract class HeadsUpManager extends AlertingNotificationManager {
                         NotificationPeekEvent.NOTIFICATION_PEEK, entry.getSbn().getUid(),
                         entry.getSbn().getPackageName(), entry.getSbn().getInstanceId());
             }
-            for (OnHeadsUpChangedListener listener : new ArrayList<>(mListeners)) {
+            for (OnHeadsUpChangedListener listener : mListeners) {
                 if (isPinned) {
                     listener.onHeadsUpPinned(entry);
                 } else {
@@ -178,7 +177,7 @@ public abstract class HeadsUpManager extends AlertingNotificationManager {
         entry.setHeadsUp(true);
         setEntryPinned((HeadsUpEntry) alertEntry, shouldHeadsUpBecomePinned(entry));
         EventLogTags.writeSysuiHeadsUpStatus(entry.getKey(), 1 /* visible */);
-        for (OnHeadsUpChangedListener listener : new ArrayList<>(mListeners)) {
+        for (OnHeadsUpChangedListener listener : mListeners) {
             listener.onHeadsUpStateChanged(entry, true);
         }
     }
@@ -189,7 +188,7 @@ public abstract class HeadsUpManager extends AlertingNotificationManager {
         entry.setHeadsUp(false);
         setEntryPinned((HeadsUpEntry) alertEntry, false /* isPinned */);
         EventLogTags.writeSysuiHeadsUpStatus(entry.getKey(), 0 /* visible */);
-        for (OnHeadsUpChangedListener listener : new ArrayList<>(mListeners)) {
+        for (OnHeadsUpChangedListener listener : mListeners) {
             listener.onHeadsUpStateChanged(entry, false);
         }
     }
@@ -207,7 +206,7 @@ public abstract class HeadsUpManager extends AlertingNotificationManager {
         if (mHasPinnedNotification) {
             MetricsLogger.count(mContext, "note_peek", 1);
         }
-        for (OnHeadsUpChangedListener listener : new ArrayList<>(mListeners)) {
+        for (OnHeadsUpChangedListener listener : mListeners) {
             listener.onHeadsUpPinnedModeChanged(hasPinnedNotification);
         }
     }

packages/SystemUI/src/com/android/systemui/util/ListenerSet.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) 2021 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.util
+
+import java.util.concurrent.CopyOnWriteArrayList
+
+/**
+ * A collection of listeners, observers, callbacks, etc.
+ *
+ * This container is optimized for infrequent mutation and frequent iteration, with thread safety
+ * and reentrant-safety guarantees as well.
+ */
+class ListenerSet<E> : Iterable<E> {
+    private val listeners: CopyOnWriteArrayList<E> = CopyOnWriteArrayList()
+
+    /**
+     * A thread-safe, reentrant-safe method to add a listener.
+     * Does nothing if the listener is already in the set.
+     */
+    fun addIfAbsent(element: E): Boolean = listeners.addIfAbsent(element)
+
+    /**
+     * A thread-safe, reentrant-safe method to remove a listener.
+     */
+    fun remove(element: E): Boolean = listeners.remove(element)
+
+    /**
+     * Returns an iterator over the listeners currently in the set.  Note that to ensure
+     * [ConcurrentModificationException] is never thrown, this iterator will not reflect changes
+     * made to the set after the iterator is constructed.
+     */
+    override fun iterator(): Iterator<E> = listeners.iterator()
+}

packages/SystemUI/tests/src/com/android/systemui/util/ListenerSetTest.kt

@@ -0,0 +1,135 @@
+/*
+ * Copyright (C) 2021 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.util
+
+import android.test.suitebuilder.annotation.SmallTest
+import androidx.test.runner.AndroidJUnit4
+import com.android.systemui.SysuiTestCase
+import com.google.common.truth.Truth.assertThat
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+
+@SmallTest
+@RunWith(AndroidJUnit4::class)
+class ListenerSetTest : SysuiTestCase() {
+
+    var runnableSet: ListenerSet<Runnable> = ListenerSet()
+
+    @Before
+    fun setup() {
+        runnableSet = ListenerSet()
+    }
+
+    @Test
+    fun addIfAbsent_doesNotDoubleAdd() {
+        // setup & preconditions
+        val runnable1 = Runnable { }
+        val runnable2 = Runnable { }
+        assertThat(runnableSet.toList()).isEmpty()
+
+        // Test that an element can be added
+        assertThat(runnableSet.addIfAbsent(runnable1)).isTrue()
+        assertThat(runnableSet.toList()).containsExactly(runnable1)
+
+        // Test that a second element can be added
+        assertThat(runnableSet.addIfAbsent(runnable2)).isTrue()
+        assertThat(runnableSet.toList()).containsExactly(runnable1, runnable2)
+
+        // Test that re-adding the first element does nothing and returns false
+        assertThat(runnableSet.addIfAbsent(runnable1)).isFalse()
+        assertThat(runnableSet.toList()).containsExactly(runnable1, runnable2)
+    }
+
+    @Test
+    fun remove_removesListener() {
+        // setup and preconditions
+        val runnable1 = Runnable { }
+        val runnable2 = Runnable { }
+        assertThat(runnableSet.toList()).isEmpty()
+        runnableSet.addIfAbsent(runnable1)
+        runnableSet.addIfAbsent(runnable2)
+        assertThat(runnableSet.toList()).containsExactly(runnable1, runnable2)
+
+        // Test that removing the first runnable only removes that one runnable
+        assertThat(runnableSet.remove(runnable1)).isTrue()
+        assertThat(runnableSet.toList()).containsExactly(runnable2)
+
+        // Test that removing a non-present runnable does not error
+        assertThat(runnableSet.remove(runnable1)).isFalse()
+        assertThat(runnableSet.toList()).containsExactly(runnable2)
+
+        // Test that removing the other runnable succeeds
+        assertThat(runnableSet.remove(runnable2)).isTrue()
+        assertThat(runnableSet.toList()).isEmpty()
+    }
+
+    @Test
+    fun remove_isReentrantSafe() {
+        // Setup and preconditions
+        val runnablesCalled = mutableListOf<Int>()
+        // runnable1 is configured to remove itself
+        val runnable1 = object : Runnable {
+            override fun run() {
+                runnableSet.remove(this)
+                runnablesCalled.add(1)
+            }
+        }
+        val runnable2 = Runnable {
+            runnablesCalled.add(2)
+        }
+        assertThat(runnableSet.toList()).isEmpty()
+        runnableSet.addIfAbsent(runnable1)
+        runnableSet.addIfAbsent(runnable2)
+        assertThat(runnableSet.toList()).containsExactly(runnable1, runnable2)
+
+        // Test that both runnables are called and 1 was removed
+        for (runnable in runnableSet) {
+            runnable.run()
+        }
+        assertThat(runnablesCalled).containsExactly(1, 2)
+        assertThat(runnableSet.toList()).containsExactly(runnable2)
+    }
+
+    @Test
+    fun addIfAbsent_isReentrantSafe() {
+        // Setup and preconditions
+        val runnablesCalled = mutableListOf<Int>()
+        val runnable99 = Runnable {
+            runnablesCalled.add(99)
+        }
+        // runnable1 is configured to add runnable99
+        val runnable1 = Runnable {
+            runnableSet.addIfAbsent(runnable99)
+            runnablesCalled.add(1)
+        }
+        val runnable2 = Runnable {
+            runnablesCalled.add(2)
+        }
+        assertThat(runnableSet.toList()).isEmpty()
+        runnableSet.addIfAbsent(runnable1)
+        runnableSet.addIfAbsent(runnable2)
+        assertThat(runnableSet.toList()).containsExactly(runnable1, runnable2)
+
+        // Test that both original runnables are called and 99 was added but not called
+        for (runnable in runnableSet) {
+            runnable.run()
+        }
+        assertThat(runnablesCalled).containsExactly(1, 2)
+        assertThat(runnableSet.toList()).containsExactly(runnable1, runnable2, runnable99)
+    }
+}