Revert "Make a change to prevent false positive background app starts." (#7278)

Reverts #7274

Reverting this if the current change is going to be included in M169. 

An additional change is needed to verify that the
`mainThreadRunnableTime` should be set only if no activity's onCreate
has been called - otherwise this can cause a regression of *genuine*
background starts.

Author: tejasd

firebase-perf/CHANGELOG.md

@@ -1,6 +1,5 @@
 # Unreleased
 * [fixed] Fixed an ANR on app launch. [#4831]
-* [fixed] Fixed app start traces on API 34+. [#5920]
 
 # 22.0.0
 * [changed] **Breaking Change**: Updated minSdkVersion to API level 23 or higher.

firebase-perf/src/main/java/com/google/firebase/perf/metrics/AppStartTrace.java

@@ -75,8 +75,6 @@ public class AppStartTrace implements ActivityLifecycleCallbacks, LifecycleObser
   private static final @NonNull Timer PERF_CLASS_LOAD_TIME = new Clock().getTime();
   private static final long MAX_LATENCY_BEFORE_UI_INIT = TimeUnit.MINUTES.toMicros(1);
 
-  private static final long MAX_BACKGROUND_RUNNABLE_DELAY = TimeUnit.MILLISECONDS.toMicros(100);
-
   // Core pool size 0 allows threads to shut down if they're idle
   private static final int CORE_POOL_SIZE = 0;
   private static final int MAX_POOL_SIZE = 1; // Only need single thread
@@ -113,8 +111,6 @@ public class AppStartTrace implements ActivityLifecycleCallbacks, LifecycleObser
   private final @Nullable Timer processStartTime;
   private final @Nullable Timer firebaseClassLoadTime;
   private Timer onCreateTime = null;
-
-  private Timer mainThreadRunnableTime = null;
   private Timer onStartTime = null;
   private Timer onResumeTime = null;
   private Timer firstForegroundTime = null;
@@ -323,26 +319,8 @@ private void recordOnDrawFrontOfQueue() {
     logExperimentTrace(this.experimentTtid);
   }
 
-  private void resolveIsStartedFromBackground() {
-    // If the mainThreadRunnableTime is null, either the runnable hasn't run, or this check has
-    // already been made.
-    if (mainThreadRunnableTime == null) {
-      return;
-    }
-
-    // Set it to true if the runnable ran more than 100ms prior to onActivityCreated()
-    if (mainThreadRunnableTime.getDurationMicros() > MAX_BACKGROUND_RUNNABLE_DELAY) {
-      isStartedFromBackground = true;
-    }
-
-    // Set this to null to prevent additional checks if `onActivityCreated()` is called again.
-    mainThreadRunnableTime = null;
-  }
-
   @Override
   public synchronized void onActivityCreated(Activity activity, Bundle savedInstanceState) {
-    resolveIsStartedFromBackground();
-
     if (isStartedFromBackground || onCreateTime != null // An activity already called onCreate()
     ) {
       return;
@@ -582,7 +560,8 @@ public static boolean isScreenOn(Context appContext) {
    * We use StartFromBackgroundRunnable to detect if app is started from background or foreground.
    * If app is started from background, we do not generate AppStart trace. This runnable is posted
    * to main UI thread from FirebasePerfEarly. If app is started from background, this runnable will
-   * be executed earlier than 100ms of any activity's onCreate() method.
+   * be executed before any activity's onCreate() method. If app is started from foreground,
+   * activity's onCreate() method is executed before this runnable.
    */
   public static class StartFromBackgroundRunnable implements Runnable {
     private final AppStartTrace trace;
@@ -593,7 +572,10 @@ public StartFromBackgroundRunnable(final AppStartTrace trace) {
 
     @Override
     public void run() {
-      trace.mainThreadRunnableTime = new Timer();
+      // if no activity has ever been created.
+      if (trace.onCreateTime == null) {
+        trace.isStartedFromBackground = true;
+      }
     }
   }
 
@@ -632,7 +614,7 @@ Timer getOnResumeTime() {
   }
 
   @VisibleForTesting
-  void setMainThreadRunnableTime(Timer timer) {
-    mainThreadRunnableTime = timer;
+  void setIsStartFromBackground() {
+    isStartedFromBackground = true;
   }
 }

firebase-perf/src/test/java/com/google/firebase/perf/metrics/AppStartTraceTest.java

@@ -18,7 +18,6 @@
 import static org.mockito.ArgumentMatchers.isA;
 import static org.mockito.Mockito.doAnswer;
 import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
@@ -239,42 +238,11 @@ public void testDelayedAppStart() {
   }
 
   @Test
-  public void testStartFromBackground_within100ms() {
+  public void testStartFromBackground() {
     FakeScheduledExecutorService fakeExecutorService = new FakeScheduledExecutorService();
-    Timer fakeTimer = spy(new Timer(currentTime));
     AppStartTrace trace =
         new AppStartTrace(transportManager, clock, configResolver, fakeExecutorService);
-    trace.registerActivityLifecycleCallbacks(appContext);
-    trace.setMainThreadRunnableTime(fakeTimer);
-
-    when(fakeTimer.getDurationMicros()).thenReturn(99L);
-    trace.onActivityCreated(activity1, bundle);
-    Assert.assertNotNull(trace.getOnCreateTime());
-    ++currentTime;
-    trace.onActivityStarted(activity1);
-    Assert.assertNotNull(trace.getOnStartTime());
-    ++currentTime;
-    trace.onActivityResumed(activity1);
-    Assert.assertNotNull(trace.getOnResumeTime());
-    fakeExecutorService.runAll();
-    // There should be a trace sent since the delay between the main thread and onActivityCreated
-    // is limited.
-    verify(transportManager, times(1))
-        .log(
-            traceArgumentCaptor.capture(),
-            ArgumentMatchers.nullable(ApplicationProcessState.class));
-  }
-
-  @Test
-  public void testStartFromBackground_moreThan100ms() {
-    FakeScheduledExecutorService fakeExecutorService = new FakeScheduledExecutorService();
-    Timer fakeTimer = spy(new Timer(currentTime));
-    AppStartTrace trace =
-        new AppStartTrace(transportManager, clock, configResolver, fakeExecutorService);
-    trace.registerActivityLifecycleCallbacks(appContext);
-    trace.setMainThreadRunnableTime(fakeTimer);
-
-    when(fakeTimer.getDurationMicros()).thenReturn(TimeUnit.MILLISECONDS.toMicros(100) + 1);
+    trace.setIsStartFromBackground();
     trace.onActivityCreated(activity1, bundle);
     Assert.assertNull(trace.getOnCreateTime());
     ++currentTime;
@@ -284,7 +252,6 @@ public void testStartFromBackground_moreThan100ms() {
     trace.onActivityResumed(activity1);
     Assert.assertNull(trace.getOnResumeTime());
     // There should be no trace sent.
-    fakeExecutorService.runAll();
     verify(transportManager, times(0))
         .log(
             traceArgumentCaptor.capture(),