Update GaugeManager and SessionManager to separate app state changes and PerfSession changes

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

@@ -51,12 +51,8 @@ public FirebasePerfEarly(
       uiExecutor.execute(new AppStartTrace.StartFromBackgroundRunnable(appStartTrace));
     }
 
-    // TODO: Bring back Firebase Sessions dependency to watch for updates to sessions.
+    // In the case of a cold start, we initialize gauge collection with a legacy PerfSession.
 
-    // In the case of cold start, we create a session and start collecting gauges as early as
-    // possible.
-    // There is code in SessionManager that prevents us from resetting the session twice in case
-    // of app cold start.
     SessionManager.getInstance().initializeGaugeCollection();
   }
 }

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

@@ -28,12 +28,19 @@ class FirebasePerformanceSessionSubscriber(override val isDataCollectionEnabled:
 
   override fun onSessionChanged(sessionDetails: SessionSubscriber.SessionDetails) {
     val currentPerfSession = SessionManager.getInstance().perfSession()
-    // TODO(b/394127311): Add logic to deal with app start gauges.
     FirebaseSessionsEnforcementCheck.checkSession(currentPerfSession, "onSessionChanged")
 
+    if (currentPerfSession.isLegacy() && currentPerfSession.isVerbose) {
+      GaugeManager.getInstance()
+        .logGaugeMetadata(sessionDetails.sessionId, ApplicationProcessState.FOREGROUND)
+      GaugeManager.getInstance()
+        .logExistingGaugeMetrics(sessionDetails.sessionId, ApplicationProcessState.FOREGROUND)
+    }
+
     val updatedSession = PerfSession.createWithId(sessionDetails.sessionId)
     SessionManager.getInstance().updatePerfSession(updatedSession)
     GaugeManager.getInstance()
       .logGaugeMetadata(updatedSession.sessionId(), ApplicationProcessState.FOREGROUND)
+    SessionManager.getInstance().updateGaugeCollectionOnNewSession()
   }
 }

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

@@ -30,7 +30,7 @@
 public class PerfSession implements Parcelable {
   private final Timer creationTime;
   private final String sessionId;
-  private boolean isGaugeAndEventCollectionEnabled = false;
+  private boolean isGaugeAndEventCollectionEnabled = true;
 
   /*
    * Creates a PerfSession object and decides what metrics to collect.

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

@@ -59,8 +59,10 @@ public class GaugeManager {
   private final TransportManager transportManager;
 
   @Nullable private GaugeMetadataManager gaugeMetadataManager;
-  @Nullable private ScheduledFuture gaugeManagerDataCollectionJob = null;
+  @Nullable private ScheduledFuture<?> gaugeManagerDataCollectionJob = null;
   @Nullable private String sessionId = null;
+
+  private boolean isCollectingGauges = false;
   private ApplicationProcessState applicationProcessState =
       ApplicationProcessState.APPLICATION_PROCESS_STATE_UNKNOWN;
 
@@ -103,6 +105,34 @@ public static synchronized GaugeManager getInstance() {
     return instance;
   }
 
+  public void updateGaugeLogging(
+      String sessionId, ApplicationProcessState applicationProcessState, long collectionFrequency) {
+    try {
+      gaugeManagerDataCollectionJob =
+          gaugeManagerExecutor
+              .get()
+              .scheduleWithFixedDelay(
+                  () -> {
+                    syncFlush(sessionId, applicationProcessState);
+                  },
+                  /* initialDelay= */ collectionFrequency
+                      * APPROX_NUMBER_OF_DATA_POINTS_PER_GAUGE_METRIC,
+                  /* period= */ collectionFrequency * APPROX_NUMBER_OF_DATA_POINTS_PER_GAUGE_METRIC,
+                  TimeUnit.MILLISECONDS);
+
+    } catch (RejectedExecutionException e) {
+      logger.warn("Unable to start collecting Gauges: " + e.getMessage());
+    }
+  }
+
+  public long updateGaugeCollection(
+      ApplicationProcessState applicationProcessState, Timer gaugeCollectionTimer) {
+    if (isCollectingGauges) {
+      stopCollectingGauges();
+    }
+    return startCollectingGauges(applicationProcessState, gaugeCollectionTimer);
+  }
+
   /**
    * Starts the collection of available gauges for the given {@code sessionId} and {@code
    * applicationProcessState}. The collected Gauge Metrics will be flushed at regular intervals.
@@ -190,7 +220,7 @@ private long startCollectingGauges(ApplicationProcessState appState, Timer refer
    *     this.stopCollectingGauges()} should always be called from the same thread.
    */
   public void stopCollectingGauges() {
-    if (this.sessionId == null) {
+    if (!this.isCollectingGauges) {
       return;
     }
 
@@ -219,6 +249,7 @@ public void stopCollectingGauges() {
                 TimeUnit.MILLISECONDS);
 
     this.sessionId = null;
+    this.isCollectingGauges = false;
     this.applicationProcessState = ApplicationProcessState.APPLICATION_PROCESS_STATE_UNKNOWN;
   }
 
@@ -253,16 +284,16 @@ private void syncFlush(String sessionId, ApplicationProcessState appState) {
   /**
    * Log the Gauge Metadata information to the transport.
    *
-   * @param aqsSessionId The {@link PerfSession#aqsSessionId()} ()} to which the collected Gauge Metrics
+   * @param sessionId The {@link PerfSession#sessionId()} ()} to which the collected Gauge Metrics
    *     should be associated with.
    * @param appState The {@link ApplicationProcessState} for which these gauges are collected.
    * @return true if GaugeMetadata was logged, false otherwise.
    */
-  public boolean logGaugeMetadata(String aqsSessionId, ApplicationProcessState appState) {
+  public boolean logGaugeMetadata(String sessionId, ApplicationProcessState appState) {
     if (gaugeMetadataManager != null) {
       GaugeMetric gaugeMetric =
           GaugeMetric.newBuilder()
-              .setSessionId(aqsSessionId)
+              .setSessionId(sessionId)
               .setGaugeMetadata(getGaugeMetadata())
               .build();
       transportManager.log(gaugeMetric, appState);
@@ -335,6 +366,22 @@ public void collectGaugeMetricOnce(Timer referenceTime) {
     collectGaugeMetricOnce(cpuGaugeCollector.get(), memoryGaugeCollector.get(), referenceTime);
   }
 
+  public void logExistingGaugeMetrics(
+      String sessionId, ApplicationProcessState applicationProcessState) {
+    // Flush any data that was collected and associate it with the given session ID and
+    // applicationProcessState.
+    @SuppressWarnings("FutureReturnValueIgnored")
+    ScheduledFuture<?> unusedFuture =
+        gaugeManagerExecutor
+            .get()
+            .schedule(
+                () -> {
+                  syncFlush(sessionId, applicationProcessState);
+                },
+                TIME_TO_WAIT_BEFORE_FLUSHING_GAUGES_QUEUE_MS,
+                TimeUnit.MILLISECONDS);
+  }
+
   private static void collectGaugeMetricOnce(
       CpuGaugeCollector cpuGaugeCollector,
       MemoryGaugeCollector memoryGaugeCollector,
@@ -405,4 +452,10 @@ private long getMemoryGaugeCollectionFrequencyMs(
       return memoryGaugeCollectionFrequency;
     }
   }
+
+  private long getGaugeLoggingFrequency(ApplicationProcessState applicationProcessState) {
+    return Math.min(
+        getMemoryGaugeCollectionFrequencyMs(applicationProcessState),
+        getCpuGaugeCollectionFrequencyMs(applicationProcessState));
+  }
 }