Does FirebaseMessagingService run in the background by default?

Question

Does the FirebaseMessagingService run in the background similar to how an IntentService operates?

I see that FirebaseMessagingService extents Service which does not run in the background, but I'd like to be sure whether or not I should be doing any work inside the FirebaseMessagingService asynchronously or synchronously.

Thank you

ANSWER:

FirebaseMessagingService's method onMessageReceived(RemoteMessage message) is NOT called on the main thread - so all work should be synchronously.

Answer 1

FirebaseMessagingService's method onMessageReceived(RemoteMessage message) is called "in the background" (not on the UI/Main thread). If you try do asynchronous work inside onMessageReceived(RemoteMessage message) you will receive an error saying:

Method execute must be called from the main thread, currently inferred thread is worker.

So all work that is done within onMessageReceived(RemoteMessage message) should be done synchronously because it's in its own background worker thread.

Answer 2

A Service does not "run in the background". A Service is just an instance of a class (ie: an object). The methods of a Service can run on either the main (UI) thread or on a background (worker) thread. It all depends on how they are called.

The lifecycle methods of the service onCreate(), onStartCommand(), onDestroy() are all called on the main (UI) thread. But in your Service you can start other threads and do other things on those threads.