“休眠”应用会收到来自 FCM 的推送通知吗？

Question

I've been reading about non-standard app killing on https://dontkillmyapp.com/ . In particular, I'm worried about how manufacturers are implementing mechanisms under the name of 'battery optimisations' which cripple the local notification API, by cancelling all alarms scheduled by an app after some time of inactivity: AlarmManager not working in several devices

Since there is no fix we as developers can implement to make local notifications work reliably, I'm wondering if I can just switch to push notifications. But I'm also not sure whether I can rely on push notifications, as there seems to be conflicting information:

Signal seem to say that their push notifications may be unreliable when battery optimisations are at work, though it's not clear whether this only applies to their custom web-socket push notification system, which it apparently uses when FCM isn't available: https://support.signal.org/hc/en-us/articles/360007318711-Troubleshooting-Notifications#android_notifications_troubleshooting_phone

It seems that push notifications which are sent via Firebase Cloud Messaging (FCM) will actually be received by the Google Play Services, so is it possible they may be received even if your app has been 'battery optimised'?

Can anyone shed some light on this? Can push notifications via FCM be more reliable than local notifications, when working around non-standard app killing?

Answer 1

Push notifications will work but still they will be affected by battery optimizations. Things like Doze mode will make your app poll-rate depend on things like user's usage of the phone; battery-level and etc.

There are things that we just cannot fight as developers and if the underlying OS decides that your app won't wake up it's better that the user gets a better phone...

Answer 2

Apparently using FCM is no guarantee that notifications will be received - they may still fail to show due to non-standard battery optimisations.

This is documented by the following article:

https://hackernoon.com/notifications-in-android-are-horribly-broken-b8dbec63f48a

Which states that:

Google GCM said that the notification was sent but there was no trace of the notification in the app's logs, it was as if the OS was swallowing notifications

After disabling battery optimisations, the notifications apparently worked again. Their workaround to this issue was:

GCM delivery receipts essentially tell you whether the device received the push notification or not. We coupled this with duplicate notification delivery receipts from inside of the app. So any device where we got ack's from GCM but not from the device, was potentially missing pushes. Once the devices were identified, we started sending them bot messages on how to add flock in their device's auto-start list.