Saving once in airplane mode breaks future cloud sync (Android)

[JVimes]

Syncing between Android devices generally works, but if I put the first device into airplane mode and do a save, then go back online, subsequent (online) saves do not make it to the second device.

• Restarting the app and clearing local app storage did not help.
• I am still able to sync the other direction (second device to first) and this seems to fix syncing first-to-second.
• I'm able to repro in my game and in ChooseSave.
• I don't see the issue when using the Google Play Games Services plugin directly (not using unity-cloud-save) in one of my other games.

Any ideas? 🫤

[gilzoide]

Well, that's weird. I don't have any ideas right now.

I don't see the issue when using the Google Play Games Services plugin directly (not using unity-cloud-save) in one of my other games.

Hmm, maybe you can help spotting what's different between the implementations. Or if you send me how you implemented it without the problem, it would help me to take a look directly into a working vs not working scenario to find what could be the problem.

[gilzoide]

Oh, and of course, thanks a lot for the bug report @JVimes!

[JVimes]

I'm happy to try to help 🙂 I've never coded for native libraries before.

Here's the source code of the method I'm calling to save bytes. I see commitAndClose there. In your code I see CommitUpdate. Maybe that difference is significant?

If that source code does not shine any light, let me know and I'll put together a sample app.

Also, the Google plugin has a smoke test app. I haven't tried it, though.

[JVimes]

Regarding my game that doesn't have the issue, it looks like the difference is probably in my code and not Google's. I wrote a simple save/load app that calls the same Google methods, passing the same arguments, and the issue appeared. I'll try to incrementally mutate the game into the save/load app to figure out what specifically brings on the issue.

[JVimes]

Alright, I narrowed down what my game is doing differently and demoed it in SaveSample.

If you can, please take a look at this commit, which works around the issue. Two things were required:

1. It saves twice
2. The first save lacks await

That last point confuses me.

[JVimes]

I reported the issue to Google here, but I don't have high hopes that they read issue reports. 🤷

[JVimes]

I was able to repro without an event and updated my above comment. Still a very strange workaround. It requires breaking the await chain.

[JVimes]

@gilzoide Turns out, this is a Play Games plugin bug (details). It would be nice to make people aware of the problem and workaround. We could implement the workaround in unity-cloud-save, or implement it in ChooseSave and reference it from the readme. Any thoughts or preference? Thanks for your help!

[gilzoide]

Hey @JVimes , sorry about the delay, I haven't really given this any attention in that time frame. That bug (and the workaround) is bonkers!

Still a very strange workaround. It requires breaking the await chain.

Maybe what "fixes" it is some kind of race condition when calling the async method twice in parallel or something like that 🤔

We could implement the workaround in unity-cloud-save, or implement it in ChooseSave and reference it from the readme. Any thoughts or preference?

If the workaround always work, I'd say we should implement in the package and document in code, maybe in README as well. "always work" in this case is like, the workaround fixes the issue, while it doesn't break the expected behavior when the bug doesn't exist, when user is always online and all.

Thanks a lot for looking into this!

---

I'm wondering now that Unity 6 has the Platform Toolkit package with support for cloud save, if it could have the same problem. Although the problem seems to be in the implementation of Play Games Services for Unity specifically, so likely not.

[JVimes]

@gilzoide no worries at all, thanks for your time!

I updated the workaround commit with proper task/exception handling.

The workaround does fine offline and online in my sample app, but I haven't stress tested. It doubles the number of CommitUpdate calls. I hope/assume the Play Games library accumulates updates and sends the result to the server on a schedule.

I didn't know about the Platform Toolkit. I'm curious, but not $210/month curious.😉