KVault.set() uses sharedPreferences.commit() instead of sharedPreferences.apply()

[rishabh876]

SharedPreference provides two ways to write changes i.e., commit() and apply(). Where commit() is a synchronous call and can block Mainthread. Whereas apply() write in-memory first followed by asynchronously to the disk. More details on apply() can be found [here](https://developer.android.com/reference/android/content/SharedPreferences.Editor#apply()).

Can we add option to use apply() by introducing a new API KVault.setAsync(... , ...)?

[benjohnde]

@rishabh876 feel free to give it a try!

[benjohnde]

@rishabh876 you can actually perform the KVault calls async, after some thinking I believe this is suboptimal, we do not really have an async alternative on iOS and just using commit does not guarantee that the shared prefs were written. Which seems to be okay (in some circumstances) for shared prefs but for secrets I would certainly want some "guarantee" rather than a "will probably be saved". You can reproduce cases in which data gets lost (commit and quick app crash or closing).

[yuroyami]

Under the hood, .commit() simply executes the operation on the current thread, whilst .apply() delegates it to an ephemeral background thread not controlled by you. .commit() rather gives you thread control, you can make use of the kotlin coroutines to do what you're aiming for:

val prefScope = CoroutineScope(Dispatchers.IO + prefMotherJob)

...

prefScope.launch {
    KVault.set()...
}

[rishabh876]

I tried moving set operation of KVault to IO thread. Turns out keystore are not thread safe on some devices. I started seeing

KeyStoreException the master key android-keystore://_androidx_security_master_key_ exists but is unusable

caused by -> IllegalBlockSizeException caused by -> KeyStoreException - Invalid operation handle

After digging a bit more I stumbled upon this thread. https://github.com/FlowCrypt/flowcrypt-android/issues/235#issuecomment-470531823 which suggests its a Thread safety issue.

I would highly recommend adding this thread-safety disclaimer in documentation of Kvault as well. It must always be used on main thread.

[cristhianescobar]

Can someone make a release with this fix please?