SignalCache can perform FileIO on the main thread.

[Dean151]

Related:

Thankfully, Marcin helped out to understand:
https://mastodon.social/@krzyzanowskim/111835373363274251

Turns out that calling .sync will block the calling thread, so the fileIO is indeed blocking the main thread, because backupCache is called from either appWillTerminate or didEnterBackground methods.

[Jeehut]

@Dean151 Thank you for reporting this. Unfortunately the Mastodon link you've posted does not work, maybe the post was deleted? In any case, the main problem with this code is that we kinda want to block the main thread before the app gets killed by the system. Or to be more precise: We want to avoid that the app gets killed while the write is in progress. If we simply put the write into a background thread, this could lead to data loss.

But I think I found a solution to this. See #187.

[Dean151]

Not sure how to reproduce.
It was just a runtime warning I got some couple times when debugging from the simulator.
I trust your fix proposal :)