Looper on a different thread for the SessionLifecycleClient's callbacks

firebase-sessions/src/main/kotlin/com/google/firebase/sessions/SessionLifecycleClient.kt

@@ -21,6 +21,7 @@ import android.content.Context
 import android.content.Intent
 import android.content.ServiceConnection
 import android.os.Handler
+import android.os.HandlerThread
 import android.os.IBinder
 import android.os.Looper
 import android.os.Message
@@ -54,13 +55,18 @@ internal object SessionLifecycleClient {
   private var serviceBound: Boolean = false
   private val queuedMessages = LinkedBlockingDeque<Message>(MAX_QUEUED_MESSAGES)
   private var curSessionId: String = ""
+  private var handlerThread: HandlerThread = HandlerThread("FirebaseSessionsClient_HandlerThread")
 
+  init {
+    handlerThread.start()
+  }
+
   /**
    * The callback class that will be used to receive updated session events from the
    * [SessionLifecycleService].
    */
   // TODO(rothbutter) should we use the main looper or is there one available in this SDK?
-  internal class ClientUpdateHandler : Handler(Looper.getMainLooper()) {
+  internal class ClientUpdateHandler : Handler(handlerThread.looper) {
     override fun handleMessage(msg: Message) {
       when (msg.what) {
         SessionLifecycleService.SESSION_UPDATED ->
@@ -144,6 +150,20 @@ internal object SessionLifecycleClient {
     sendLifecycleEvent(SessionLifecycleService.BACKGROUNDED)
   }
 
+  /**
+   * Perform initialization that requires cleanup
+   */
+  fun started() {
+    if (!handlerThread.isAlive) { handlerThread.start() }
+  }
+
+  /**
+   * Cleanup initialization
+   */
+  fun stopped() {
+    handlerThread.quit()
+  }
+
   /**
    * Sends a message to the [SessionLifecycleService] with the given event code. This will
    * potentially also send any messages that have been queued up but not successfully delivered to

firebase-sessions/src/main/kotlin/com/google/firebase/sessions/SessionsActivityLifecycleCallbacks.kt

@@ -31,9 +31,9 @@ internal object SessionsActivityLifecycleCallbacks : ActivityLifecycleCallbacks
 
   override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) = Unit
 
-  override fun onActivityStarted(activity: Activity) = Unit
+  override fun onActivityStarted(activity: Activity) = SessionLifecycleClient.started()
 
-  override fun onActivityStopped(activity: Activity) = Unit
+  override fun onActivityStopped(activity: Activity) = SessionLifecycleClient.stopped()
 
   override fun onActivityDestroyed(activity: Activity) = Unit