Re-introduce gauge collection for app start

Author: tejasd

firebase-perf/src/main/java/com/google/firebase/perf/logging/DebugEnforcementCheck.kt

@@ -16,15 +16,18 @@
 
 package com.google.firebase.perf.logging
 
+import com.google.firebase.perf.session.PerfSession
+import com.google.firebase.perf.session.isLegacy
+
 class DebugEnforcementCheck {
   companion object {
     /** When enabled, failed preconditions will cause assertion errors for debugging. */
     @JvmStatic var enforcement: Boolean = false
     private var logger: AndroidLogger = AndroidLogger.getInstance()
 
-    public fun checkSession(isAqsAvailable: Boolean, failureMessage: String) {
-      if (!isAqsAvailable) {
-        Companion.logger.debug(failureMessage)
+    public fun checkSession(session: PerfSession, failureMessage: String) {
+      if (session.isLegacy()) {
+        logger.debug("legacy session ${session.sessionId()}: $failureMessage")
         assert(!enforcement) { failureMessage }
       }
     }

firebase-perf/src/main/java/com/google/firebase/perf/session/FirebasePerformanceSessionSubscriber.kt

@@ -16,10 +16,10 @@
 
 package com.google.firebase.perf.session
 
+import com.google.firebase.perf.logging.DebugEnforcementCheck
 import com.google.firebase.perf.session.gauges.GaugeManager
 import com.google.firebase.perf.v1.ApplicationProcessState
 import com.google.firebase.sessions.api.SessionSubscriber
-import java.util.UUID
 
 class FirebasePerformanceSessionSubscriber(override val isDataCollectionEnabled: Boolean) :
   SessionSubscriber {
@@ -28,15 +28,21 @@ class FirebasePerformanceSessionSubscriber(override val isDataCollectionEnabled:
 
   override fun onSessionChanged(sessionDetails: SessionSubscriber.SessionDetails) {
     val currentPerfSession = SessionManager.getInstance().perfSession()
+    DebugEnforcementCheck.checkSession(currentPerfSession, "onSessionChanged")
 
     // A [PerfSession] was created before a session was started.
-    if (!currentPerfSession.isAQS()) {
+    // Since these was gauge collection with app startup, it logs them to the updated session ID.
+    if (currentPerfSession.isLegacy()) {
       GaugeManager.getInstance()
-        .logGaugeMetadata(currentPerfSession.sessionId(), ApplicationProcessState.FOREGROUND)
-      return
+        .logGaugeMetadata(sessionDetails.sessionId, ApplicationProcessState.FOREGROUND)
+      GaugeManager.getInstance()
+        .stopCollectingGaugesForLegacySession(
+          sessionDetails.sessionId,
+          ApplicationProcessState.FOREGROUND
+        )
     }
 
-    val updatedSession = PerfSession.createWithId(UUID.randomUUID().toString())
+    val updatedSession = PerfSession.createWithId(sessionDetails.sessionId)
     SessionManager.getInstance().updatePerfSession(updatedSession)
     GaugeManager.getInstance()
       .logGaugeMetadata(updatedSession.sessionId(), ApplicationProcessState.FOREGROUND)

firebase-perf/src/main/java/com/google/firebase/perf/session/FirebaseSessionsHelper.kt

@@ -3,11 +3,12 @@ package com.google.firebase.perf.session
 import com.google.firebase.perf.util.Constants
 import java.util.UUID
 
-/** Identifies whether the [PerfSession] is an AQS or not. */
-fun PerfSession.isAQS(): Boolean {
-  return !this.sessionId().startsWith(Constants.UNDEFINED_AQS_ID_PREFIX)
+/** Identifies whether the [PerfSession] is legacy or not. */
+fun PerfSession.isLegacy(): Boolean {
+  return this.sessionId().startsWith(Constants.UNDEFINED_AQS_ID_PREFIX)
 }
 
+/** Creates a valid session ID for [PerfSession] that can be predictably identified as legacy. */
 fun createLegacySessionId(): String {
   val uuid = UUID.randomUUID().toString().replace("-", "")
   return uuid.replaceRange(

firebase-perf/src/main/java/com/google/firebase/perf/session/SessionManager.java

@@ -20,6 +20,7 @@
 import androidx.annotation.VisibleForTesting;
 import com.google.firebase.perf.application.AppStateMonitor;
 import com.google.firebase.perf.application.AppStateUpdateHandler;
+import com.google.firebase.perf.logging.DebugEnforcementCheck;
 import com.google.firebase.perf.session.gauges.GaugeManager;
 import com.google.firebase.perf.v1.ApplicationProcessState;
 import com.google.firebase.perf.v1.GaugeMetadata;
@@ -29,7 +30,6 @@
 import java.util.Iterator;
 import java.util.Objects;
 import java.util.Set;
-import java.util.UUID;
 
 /** Session manager to generate sessionIDs and broadcast to the application. */
 @Keep // Needed because of b/117526359.
@@ -51,15 +51,13 @@ public static SessionManager getInstance() {
 
   /** Returns the currently active PerfSession. */
   public final PerfSession perfSession() {
+    DebugEnforcementCheck.Companion.checkSession(perfSession, "SessionManager.perfSession()");
     return perfSession;
   }
 
   private SessionManager() {
     // Generate a new sessionID for every cold start.
-    this(
-        GaugeManager.getInstance(),
-        PerfSession.createWithId(UUID.randomUUID().toString()),
-        AppStateMonitor.getInstance());
+    this(GaugeManager.getInstance(), PerfSession.createWithId(null), AppStateMonitor.getInstance());
   }
 
   @VisibleForTesting

firebase-perf/src/main/java/com/google/firebase/perf/session/gauges/GaugeManager.java

@@ -245,6 +245,40 @@ public void stopCollectingGauges() {
                 TimeUnit.MILLISECONDS);
   }
 
+  /**
+   * Stops the collection of gauges if it was currently collecting them for a legacy session.
+   *
+   * @note: This method is NOT thread safe - {@link this.startCollectingGauges()} and {@link
+   *     this.stopCollectingGauges()} should always be called from the same thread.
+   */
+  public void stopCollectingGaugesForLegacySession(
+      String updatedSessionId, ApplicationProcessState flushToApplicationProcessState) {
+    final ApplicationProcessState applicationProcessStateForScheduledTask =
+        flushToApplicationProcessState;
+
+    cpuGaugeCollector.get().stopCollecting();
+    memoryGaugeCollector.get().stopCollecting();
+
+    if (gaugeManagerDataCollectionJob != null) {
+      gaugeManagerDataCollectionJob.cancel(false);
+    }
+
+    final String sessionIdForScheduledTask = updatedSessionId;
+    this.session = null;
+
+    // Flush any data that was collected for this session one last time.
+    @SuppressWarnings("FutureReturnValueIgnored")
+    ScheduledFuture<?> unusedFuture =
+        gaugeManagerExecutor
+            .get()
+            .schedule(
+                () -> {
+                  syncFlush(sessionIdForScheduledTask, applicationProcessStateForScheduledTask);
+                },
+                TIME_TO_WAIT_BEFORE_FLUSHING_GAUGES_QUEUE_MS,
+                TimeUnit.MILLISECONDS);
+  }
+
   /**
    * This method reads any pending data points from all the Gauge's queues, assembles a GaugeMetric
    * proto and logs it to transport.
@@ -433,7 +467,7 @@ private long getMemoryGaugeCollectionFrequencyMs(
 
   private boolean isValidSessionForLogging() {
     if (session == null) return false;
-    return session.isGaugeAndEventCollectionEnabled() && FirebaseSessionsHelperKt.isAQS(session);
+    return session.isGaugeAndEventCollectionEnabled() && FirebaseSessionsHelperKt.isLegacy(session);
   }
 
   @VisibleForTesting

firebase-perf/src/test/java/com/google/firebase/perf/session/PerfSessionTest.java

@@ -68,7 +68,7 @@ public void instanceCreation() {
     assertThat(session.isVerbose()).isTrue();
     session.setGaugeAndEventCollectionEnabled(false);
     assertThat(session.isVerbose()).isFalse();
-    assertThat(FirebaseSessionsHelperKt.isAQS(session)).isTrue();
+    assertThat(FirebaseSessionsHelperKt.isLegacy(session)).isTrue();
   }
 
   @Test
@@ -79,7 +79,7 @@ public void legacyInstanceCreation() {
     assertThat(perfSession.isVerbose()).isTrue();
     perfSession.setGaugeAndEventCollectionEnabled(false);
     assertThat(perfSession.isVerbose()).isFalse();
-    assertThat(FirebaseSessionsHelperKt.isAQS(perfSession)).isFalse();
+    assertThat(FirebaseSessionsHelperKt.isLegacy(perfSession)).isFalse();
   }
 
   @Test