Refactor startup executor (#6040)

- Use backgroundExecutorService from firebase common executor to process
setting fetch task
- Remove some legacy logic

#no-changelog

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/FirebaseCrashlytics.java

@@ -48,6 +48,7 @@
 import com.google.firebase.sessions.api.FirebaseSessionsDependencies;
 import java.util.List;
 import java.util.concurrent.Callable;
+import java.util.concurrent.Executor;
 import java.util.concurrent.ExecutorService;
 
 /**
@@ -71,7 +72,7 @@ public class FirebaseCrashlytics {
       @NonNull Deferred<CrashlyticsNativeComponent> nativeComponent,
       @NonNull Deferred<AnalyticsConnector> analyticsConnector,
       @NonNull Deferred<FirebaseRemoteConfigInterop> remoteConfigInteropDeferred,
-      @Background ExecutorService liteExecutorService,
+      @Background ExecutorService backgroundExecutorService,
       @Blocking ExecutorService blockingExecutorService) {
 
     Context context = app.getApplicationContext();
@@ -151,8 +152,8 @@ public class FirebaseCrashlytics {
 
     Logger.getLogger().v("Installer package name is: " + appData.installerPackageName);
 
-    final ExecutorService threadPoolExecutor =
-        ExecutorUtils.buildSingleThreadExecutorService("com.google.firebase.crashlytics.startup");
+    final Executor threadPoolExecutor =
+        ExecutorUtils.buildSequentialExecutor(backgroundExecutorService);
 
     final SettingsController settingsController =
         SettingsController.create(
@@ -182,17 +183,9 @@ public Object then(@NonNull Task<Void> task) throws Exception {
 
     final boolean finishCoreInBackground = core.onPreExecute(appData, settingsController);
 
-    Tasks.call(
-        threadPoolExecutor,
-        new Callable<Void>() {
-          @Override
-          public Void call() throws Exception {
-            if (finishCoreInBackground) {
-              core.doBackgroundInitializationAsync(settingsController);
-            }
-            return null;
-          }
-        });
+    if (finishCoreInBackground) {
+      core.doBackgroundInitializationAsync(settingsController);
+    }
 
     return new FirebaseCrashlytics(core);
   }

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/ExecutorUtils.java

@@ -17,8 +17,11 @@
 import static java.util.concurrent.TimeUnit.SECONDS;
 
 import android.annotation.SuppressLint;
+
+import com.google.firebase.concurrent.FirebaseExecutors;
 import com.google.firebase.crashlytics.internal.Logger;
 import java.util.Locale;
+import java.util.concurrent.Executor;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.LinkedBlockingQueue;
@@ -34,6 +37,10 @@ public final class ExecutorUtils {
 
   private ExecutorUtils() {}
 
+  public static Executor buildSequentialExecutor(Executor commonExecutor) {
+    return FirebaseExecutors.newSequentialExecutor(commonExecutor);
+  }
+
   public static ExecutorService buildSingleThreadExecutorService(String name) {
     final ThreadFactory threadFactory = ExecutorUtils.getNamedThreadFactory(name);
     final ExecutorService executor =