Make FirebasePerformance initialization lazy. (#2518)

* Make FirebasePerformane initialization lazy.

* Fix failing tests.

* Add tests for FirebasePerformance initialization.

* Add FirebasePerformanceInitializer and register it to AppStateMonitor cold start.

* Hide FirebasePerformanceInitializer api

* Add tests for appStateMonitor.

* Address comments.

Author: jeremyjiang-dev

firebase-perf/src/main/java/com/google/firebase/perf/FirebasePerfRegistrar.java

@@ -52,12 +52,14 @@ public List<Component<?>> getComponents() {
             .add(Dependency.required(FirebaseInstallationsApi.class))
             .add(Dependency.requiredProvider(TransportFactory.class))
             .factory(FirebasePerfRegistrar::providesFirebasePerformance)
-            // Since the SDK is eager(auto starts at app start), we use "lazy" dependency for some
-            // components that are not required during initialization so as not to force initialize
-            // them at app startup (refer
-            // https://github.com/google/guice/wiki/InjectingProviders#providers-for-lazy-loading).
-            .eagerInDefaultApp()
             .build(),
+        /**
+         * Fireperf SDK is lazily by {@link FirebasePerformanceInitializer} during {@link
+         * com.google.firebase.perf.application.AppStateMonitor#onActivityResumed(Activity)}. we use
+         * "lazy" dependency for some components that are not required during initialization so as
+         * not to force initialize them at app startup (refer
+         * https://github.com/google/guice/wiki/InjectingProviders#providers-for-lazy-loading)*
+         */
         LibraryVersionComponent.create("fire-perf", BuildConfig.VERSION_NAME));
   }
 

firebase-perf/src/main/java/com/google/firebase/perf/FirebasePerformanceInitializer.java

@@ -0,0 +1,33 @@
+// Copyright 2021 Google LLC
+//
+// 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.google.firebase.perf;
+
+import com.google.firebase.perf.application.AppStateMonitor;
+
+/**
+ * FirebasePerformanceInitializer to initialize FirebasePerformance during app cold start
+ *
+ * @hide
+ */
+/** @hide */
+public final class FirebasePerformanceInitializer implements AppStateMonitor.AppColdStartCallback {
+
+  /** @hide */
+  @Override
+  public void onAppColdStart() {
+    // Initialize FirebasePerformance when app cold starts.
+    FirebasePerformance.getInstance();
+  }
+}

firebase-perf/src/main/java/com/google/firebase/perf/application/AppStateMonitor.java

@@ -85,8 +85,9 @@ public static AppStateMonitor getInstance() {
 
   private ApplicationProcessState mCurrentState = ApplicationProcessState.BACKGROUND;
 
-  private Set<WeakReference<AppStateCallback>> mClients =
+  private Set<WeakReference<AppStateCallback>> appStateSubscribers =
       new HashSet<WeakReference<AppStateCallback>>();
+  private Set<AppColdStartCallback> appColdStartSubscribers = new HashSet<AppColdStartCallback>();
 
   private boolean hasFrameMetricsAggregator = false;
   private FrameMetricsAggregator mFrameMetricsAggregator;
@@ -207,6 +208,7 @@ public synchronized void onActivityResumed(Activity activity) {
       updateAppState(ApplicationProcessState.FOREGROUND);
       if (mIsColdStart) {
         // case 1: app startup.
+        sendAppColdStartUpdate();
         mIsColdStart = false;
       } else {
         // case 2: app switch from background to foreground.
@@ -234,36 +236,50 @@ public ApplicationProcessState getAppState() {
   }
 
   /**
-   * Register a client to receive app state update.
+   * Register a subscriber to receive app state update.
    *
    * @param client an AppStateCallback instance.
    * @hide
    */
   /** @hide */
-  public void registerForAppState(WeakReference<AppStateCallback> client) {
-    synchronized (mClients) {
-      mClients.add(client);
+  public void registerForAppState(WeakReference<AppStateCallback> subscriber) {
+    synchronized (appStateSubscribers) {
+      appStateSubscribers.add(subscriber);
     }
   }
 
   /**
-   * Unregister the client to stop receiving app state update.
+   * Unregister the subscriber to stop receiving app state update.
    *
-   * @param client an AppStateCallback instance.
+   * @param subscriber an AppStateCallback instance.
    * @hide
    */
   /** @hide */
-  public void unregisterForAppState(WeakReference<AppStateCallback> client) {
-    synchronized (mClients) {
-      mClients.remove(client);
+  public void unregisterForAppState(WeakReference<AppStateCallback> subscriber) {
+    synchronized (appStateSubscribers) {
+      appStateSubscribers.remove(subscriber);
     }
   }
 
-  /** Send update state update to registered clients. */
+  /**
+   * Register a subscriber to receive app cold start update.
+   *
+   * @param subscriber the {@link AppColdStartCallback} instance.
+   * @hide
+   */
+  /** @hide */
+  public void registerForAppColdStart(AppColdStartCallback subscriber) {
+    synchronized (appStateSubscribers) {
+      appColdStartSubscribers.add(subscriber);
+    }
+  }
+
+  /** Send update state update to registered subscribers. */
   private void updateAppState(ApplicationProcessState newState) {
     mCurrentState = newState;
-    synchronized (mClients) {
-      for (Iterator<WeakReference<AppStateCallback>> i = mClients.iterator(); i.hasNext(); ) {
+    synchronized (appStateSubscribers) {
+      for (Iterator<WeakReference<AppStateCallback>> i = appStateSubscribers.iterator();
+          i.hasNext(); ) {
         AppStateCallback callback = i.next().get();
         if (callback != null) {
           callback.onUpdateAppState(mCurrentState);
@@ -276,6 +292,18 @@ private void updateAppState(ApplicationProcessState newState) {
     }
   }
 
+  /** Send cold start update to registered subscribers. */
+  private void sendAppColdStartUpdate() {
+    synchronized (appStateSubscribers) {
+      for (Iterator<AppColdStartCallback> i = appColdStartSubscribers.iterator(); i.hasNext(); ) {
+        AppColdStartCallback callback = i.next();
+        if (callback != null) {
+          callback.onAppColdStart();
+        }
+      }
+    }
+  }
+
   /**
    * Return app is in foreground or not.
    *
@@ -425,7 +453,7 @@ private boolean hasFrameMetricsAggregatorClass() {
   }
 
   /**
-   * An interface to be implemented by clients which needs to receive app state update.
+   * An interface to be implemented by subscribers which needs to receive app state update.
    *
    * @hide
    */
@@ -436,6 +464,15 @@ public static interface AppStateCallback {
     public void onUpdateAppState(ApplicationProcessState newState);
   }
 
+  /**
+   * An interface to be implemented by subscribers which needs to receive app cold start update.
+   *
+   * @hide
+   */
+  public static interface AppColdStartCallback {
+    public void onAppColdStart();
+  }
+
   /**
    * Screen trace name is prefix "_st_" concatenates with Activity's class name.
    *

firebase-perf/src/main/java/com/google/firebase/perf/provider/FirebasePerfProvider.java

@@ -28,6 +28,7 @@
 import androidx.annotation.Nullable;
 import com.google.android.gms.common.internal.Preconditions;
 import com.google.android.gms.common.util.VisibleForTesting;
+import com.google.firebase.perf.FirebasePerformanceInitializer;
 import com.google.firebase.perf.application.AppStateMonitor;
 import com.google.firebase.perf.config.ConfigResolver;
 import com.google.firebase.perf.metrics.AppStartTrace;
@@ -61,7 +62,10 @@ public void attachInfo(Context context, ProviderInfo info) {
     ConfigResolver configResolver = ConfigResolver.getInstance();
     configResolver.setContentProviderContext(getContext());
 
-    AppStateMonitor.getInstance().registerActivityLifecycleCallbacks(getContext());
+    AppStateMonitor appStateMonitor = AppStateMonitor.getInstance();
+    appStateMonitor.registerActivityLifecycleCallbacks(getContext());
+    appStateMonitor.registerForAppColdStart(new FirebasePerformanceInitializer());
+
     AppStartTrace appStartTrace = AppStartTrace.getInstance();
     appStartTrace.registerActivityLifecycleCallbacks(getContext());
 

firebase-perf/src/test/java/com/google/firebase/perf/FirebasePerfRegistrarTest.java

@@ -48,6 +48,6 @@ public void testGetComponents() {
             Dependency.required(FirebaseInstallationsApi.class),
             Dependency.requiredProvider(TransportFactory.class));
 
-    assertThat(firebasePerfComponent.isEagerInDefaultApp()).isTrue();
+    assertThat(firebasePerfComponent.isLazy()).isTrue();
   }
 }

firebase-perf/src/test/java/com/google/firebase/perf/application/AppStateMonitorTest.java

@@ -32,6 +32,7 @@
 import android.content.Context;
 import android.os.Bundle;
 import android.view.WindowManager.LayoutParams;
+import com.google.firebase.perf.FirebasePerformanceInitializer;
 import com.google.firebase.perf.FirebasePerformanceTestBase;
 import com.google.firebase.perf.config.ConfigResolver;
 import com.google.firebase.perf.config.DeviceCacheManager;
@@ -675,51 +676,106 @@ public void backgroundTrace_perfMonDeactivated_traceCreated() {
   }
 
   @Test
-  public void activityStateChanges_singleClient_callbackIsCalled() {
+  public void activityStateChanges_singleSubscriber_callbackIsCalled() {
     AppStateMonitor monitor = new AppStateMonitor(transportManager, mClock);
-    Map<Integer, ApplicationProcessState> clientState = new HashMap<>();
+    Map<Integer, ApplicationProcessState> subscriberState = new HashMap<>();
 
-    final int client1 = 1;
+    final int subscriber1 = 1;
     monitor.registerForAppState(
-        new WeakReference<>(newState -> clientState.put(client1, newState)));
+        new WeakReference<>(newState -> subscriberState.put(subscriber1, newState)));
 
     // Activity comes to Foreground
     monitor.onActivityResumed(activity1);
-    assertThat(clientState.get(client1)).isEqualTo(ApplicationProcessState.FOREGROUND);
+    assertThat(subscriberState.get(subscriber1)).isEqualTo(ApplicationProcessState.FOREGROUND);
 
     // Activity goes to Background
     monitor.onActivityStopped(activity1);
-    assertThat(clientState.get(client1)).isEqualTo(ApplicationProcessState.BACKGROUND);
+    assertThat(subscriberState.get(subscriber1)).isEqualTo(ApplicationProcessState.BACKGROUND);
   }
 
   @Test
-  public void activityStateChanges_multipleClients_callbackCalledOnEachClient() {
+  public void activityStateChanges_multipleSubscribers_callbackCalledOnEachSubscriber() {
     AppStateMonitor monitor = new AppStateMonitor(transportManager, mClock);
-    Map<Integer, ApplicationProcessState> clientState = new HashMap<>();
+    Map<Integer, ApplicationProcessState> subscriberState = new HashMap<>();
 
-    final int client1 = 1;
+    final int subscriber1 = 1;
     monitor.registerForAppState(
-        new WeakReference<>(newState -> clientState.put(client1, newState)));
+        new WeakReference<>(newState -> subscriberState.put(subscriber1, newState)));
 
-    final int client2 = 2;
+    final int subscriber2 = 2;
     monitor.registerForAppState(
-        new WeakReference<>(newState -> clientState.put(client2, newState)));
+        new WeakReference<>(newState -> subscriberState.put(subscriber2, newState)));
 
-    final int client3 = 3;
+    final int subscriber3 = 3;
     monitor.registerForAppState(
-        new WeakReference<>(newState -> clientState.put(client3, newState)));
+        new WeakReference<>(newState -> subscriberState.put(subscriber3, newState)));
 
     // Activity comes to Foreground
     monitor.onActivityResumed(activity1);
-    assertThat(clientState.get(client1)).isEqualTo(ApplicationProcessState.FOREGROUND);
-    assertThat(clientState.get(client2)).isEqualTo(ApplicationProcessState.FOREGROUND);
-    assertThat(clientState.get(client3)).isEqualTo(ApplicationProcessState.FOREGROUND);
+    assertThat(subscriberState.get(subscriber1)).isEqualTo(ApplicationProcessState.FOREGROUND);
+    assertThat(subscriberState.get(subscriber2)).isEqualTo(ApplicationProcessState.FOREGROUND);
+    assertThat(subscriberState.get(subscriber3)).isEqualTo(ApplicationProcessState.FOREGROUND);
 
     // Activity goes to Background
     monitor.onActivityStopped(activity1);
-    assertThat(clientState.get(client1)).isEqualTo(ApplicationProcessState.BACKGROUND);
-    assertThat(clientState.get(client2)).isEqualTo(ApplicationProcessState.BACKGROUND);
-    assertThat(clientState.get(client3)).isEqualTo(ApplicationProcessState.BACKGROUND);
+    assertThat(subscriberState.get(subscriber1)).isEqualTo(ApplicationProcessState.BACKGROUND);
+    assertThat(subscriberState.get(subscriber2)).isEqualTo(ApplicationProcessState.BACKGROUND);
+    assertThat(subscriberState.get(subscriber3)).isEqualTo(ApplicationProcessState.BACKGROUND);
+  }
+
+  @Test
+  public void appColdStart_singleSubscriber_callbackIsCalled() {
+    AppStateMonitor monitor = new AppStateMonitor(transportManager, mClock);
+    FirebasePerformanceInitializer mockInitializer = mock(FirebasePerformanceInitializer.class);
+    monitor.registerForAppColdStart(mockInitializer);
+
+    // Activity comes to Foreground
+    monitor.onActivityResumed(activity1);
+    verify(mockInitializer, times(1)).onAppColdStart();
+  }
+
+  @Test
+  public void appHotStart_singleSubscriber_callbackIsNotCalled() {
+    AppStateMonitor monitor = new AppStateMonitor(transportManager, mClock);
+    FirebasePerformanceInitializer mockInitializer = mock(FirebasePerformanceInitializer.class);
+    monitor.registerForAppColdStart(mockInitializer);
+
+    // Activity comes to Foreground
+    monitor.onActivityResumed(activity1);
+    verify(mockInitializer, times(1)).onAppColdStart();
+
+    // Activity goes to Background
+    monitor.onActivityStopped(activity1);
+
+    // Activity comes to Foreground
+    monitor.onActivityResumed(activity1);
+    verify(mockInitializer, times(1)).onAppColdStart();
+  }
+
+  @Test
+  public void appColdStart_multipleSubscriber_callbackIsCalled() {
+    AppStateMonitor monitor = new AppStateMonitor(transportManager, mClock);
+    FirebasePerformanceInitializer mockInitializer1 = mock(FirebasePerformanceInitializer.class);
+    FirebasePerformanceInitializer mockInitializer2 = mock(FirebasePerformanceInitializer.class);
+    monitor.registerForAppColdStart(mockInitializer1);
+    monitor.registerForAppColdStart(mockInitializer2);
+
+    // Activity comes to Foreground
+    monitor.onActivityResumed(activity1);
+    verify(mockInitializer1, times(1)).onAppColdStart();
+    verify(mockInitializer2, times(1)).onAppColdStart();
+  }
+
+  @Test
+  public void appColdStart_singleSubscriberRegistersForMultipleTimes_oneCallbackIsCalled() {
+    AppStateMonitor monitor = new AppStateMonitor(transportManager, mClock);
+    FirebasePerformanceInitializer mockInitializer1 = mock(FirebasePerformanceInitializer.class);
+    monitor.registerForAppColdStart(mockInitializer1);
+    monitor.registerForAppColdStart(mockInitializer1);
+
+    // Activity comes to Foreground
+    monitor.onActivityResumed(activity1);
+    verify(mockInitializer1, times(1)).onAppColdStart();
   }
 
   private static Activity createFakeActivity(boolean isHardwareAccelerated) {