From 4049d0fd9ce283617079a341916cc423fed62c80 Mon Sep 17 00:00:00 2001
From: Kweku Adams <kwekua@google.com>
Date: Tue, 10 Aug 2021 08:31:30 -0700
Subject: [PATCH] Improve forEach.

The default implementation of Collection.forEach() uses the
iterator(). Switch to a simple for loop iterating through the array
since the iterator is an inefficient way to access the array contents.

Benchmark results:

Before:

android.util.ArrayMapPerfTest#testForEach_Large:
	forEach_Large_min (ns): 599759
	forEach_Large_median (ns): 655845
	forEach_Large_mean (ns): 636927
	forEach_Large_standardDeviation: 34373
android.util.ArrayMapPerfTest#testForEach_Small:
	forEach_Small_min (ns): 118822
	forEach_Small_median (ns): 121422
	forEach_Small_mean (ns): 121695
	forEach_Small_standardDeviation: 2079

After:

android.util.ArrayMapPerfTest#testForEach_Large:
	forEach_Large_min (ns): 403562
	forEach_Large_median (ns): 441364
	forEach_Large_mean (ns): 442301
	forEach_Large_standardDeviation: 24917
android.util.ArrayMapPerfTest#testForEach_Small:
	forEach_Small_min (ns): 81889
	forEach_Small_median (ns): 87889
	forEach_Small_mean (ns): 86905
	forEach_Small_standardDeviation: 2880

Bug: 194098491
Test: atest CorePerfTests:ArrayMapPerfTest (see results above)
Test: atest CtsUtilTestCases:ArrayMapTest
Test: atest FrameworksCoreTests:ArrayMapTest
Change-Id: Id528fe24f1d17af01a2d639753d42e2ad21144d2
---
 .../src/android/util/ArrayMapPerfTest.java    | 72 +++++++++++++++++++
 core/java/android/util/ArrayMap.java          | 23 ++++++
 2 files changed, 95 insertions(+)
 create mode 100644 apct-tests/perftests/core/src/android/util/ArrayMapPerfTest.java

diff --git a/apct-tests/perftests/core/src/android/util/ArrayMapPerfTest.java b/apct-tests/perftests/core/src/android/util/ArrayMapPerfTest.java
new file mode 100644
index 0000000000000..b93a6ea18d8db
--- /dev/null
+++ b/apct-tests/perftests/core/src/android/util/ArrayMapPerfTest.java
@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2018 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 android.util;
+
+import android.perftests.utils.BenchmarkState;
+import android.perftests.utils.PerfStatusReporter;
+
+import androidx.test.filters.LargeTest;
+import androidx.test.runner.AndroidJUnit4;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.util.function.BiConsumer;
+
+@RunWith(AndroidJUnit4.class)
+@LargeTest
+public class ArrayMapPerfTest {
+    private static final int NUM_ITERATIONS = 100;
+    private static final int SET_SIZE_SMALL = 10;
+    private static final int SET_SIZE_LARGE = 50;
+
+    @Rule
+    public PerfStatusReporter mPerfStatusReporter = new PerfStatusReporter();
+
+    @Test
+    public void testForEach_Small() {
+        BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        BiConsumer<String, Integer> consumer = (s, i) -> {
+        };
+        while (state.keepRunning()) {
+            for (int i = 0; i < NUM_ITERATIONS; ++i) {
+                ArrayMap<String, Integer> map = new ArrayMap<>();
+                for (int j = 0; j < SET_SIZE_SMALL; j++) {
+                    map.put(Integer.toString(j), j);
+                }
+                map.forEach(consumer);
+            }
+        }
+    }
+
+    @Test
+    public void testForEach_Large() {
+        BenchmarkState state = mPerfStatusReporter.getBenchmarkState();
+        BiConsumer<String, Integer> consumer = (s, i) -> {
+        };
+        while (state.keepRunning()) {
+            for (int i = 0; i < NUM_ITERATIONS; ++i) {
+                ArrayMap<String, Integer> map = new ArrayMap<>();
+                for (int j = 0; j < SET_SIZE_LARGE; j++) {
+                    map.put(Integer.toString(j), j);
+                }
+                map.forEach(consumer);
+            }
+        }
+    }
+}
diff --git a/core/java/android/util/ArrayMap.java b/core/java/android/util/ArrayMap.java
index 4edff27d0ced4..f50b51bbdb356 100644
--- a/core/java/android/util/ArrayMap.java
+++ b/core/java/android/util/ArrayMap.java
@@ -27,6 +27,7 @@ import java.util.Collection;
 import java.util.ConcurrentModificationException;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.BiConsumer;
 
 /**
  * ArrayMap is a generic key->value mapping data structure that is
@@ -979,6 +980,28 @@ public final class ArrayMap<K, V> implements Map<K, V> {
         return MapCollections.containsAllHelper(this, collection);
     }
 
+    /**
+     * Performs the given action for all elements in the stored order. This implementation overrides
+     * the default implementation to avoid iterating using the {@link #entrySet()} and iterates in
+     * the key-value order consistent with {@link #keyAt(int)} and {@link #valueAt(int)}.
+     *
+     * @param action The action to be performed for each element
+     */
+    @Override
+    public void forEach(BiConsumer<? super K, ? super V> action) {
+        if (action == null) {
+            throw new NullPointerException("action must not be null");
+        }
+
+        final int size = mSize;
+        for (int i = 0; i < size; ++i) {
+            if (size != mSize) {
+                throw new ConcurrentModificationException();
+            }
+            action.accept(keyAt(i), valueAt(i));
+        }
+    }
+
     /**
      * Perform a {@link #put(Object, Object)} of all key/value pairs in <var>map</var>
      * @param map The map whose contents are to be retrieved.