[BUG] Calling store.get() in RoomDatabase.withTransaction will encounter a deadlock

[yaoandy107]

Describe the bug When I call store.get() in the RoomDatabase.withTransaction {} and the store trigger the writer to write data into the database, a deadlock will occur. Everything is fine if the writer does not trigger or calling the store.get() outside the withTransaction {}.

To Reproduce

1. clear the Room's table that the Store used
2. call store.get() inside the RoomDatabase.withTransaction {}

Sample code (Full sample):

viewLifecycleOwner.lifecycleScope.launch {
    appDatabase.forumDao().deleteAll()
    // The transaction work fine if uncomment the line below
    // forumStore.get(ForumKey(id = "1"))
    appDatabase.withTransaction {
        Log.d("TEST", "Start transaction")
        forumStore.get(ForumKey(id = "1"))
        Log.d("TEST", "End transaction")
    }
}

Expected behavior

1. According to the sample above, either the "End transaction" should print or the error log should appear

Smartphone (please complete the following information):

• Device: Emulator Pixel_4_API_33
• OS: Android 13
• Store Version: 4.0.5

[digitalbuddha]

Thank you for reporting and including a sample ❤️. I can take a look this week and let you know a fix/suggestion. My initial thinking is the transaction is locking writing to the db within your block. Without writing we can't read.

[digitalbuddha]

This looks related. https://issuetracker.google.com/issues/120854786 Seems like there is a runInTransaction function when working with suspend and transactions in room

[digitalbuddha]

Do you mind trying the new transaction api and reporting back if it works?

[yaoandy107]

Thanks for your fast reply. The runInTransaction() can't support suspend function, so it can't replace withTransaction(). Besides, the withTransaction() is the new API introduced in the issue you posted above.

[yaoandy107]

I find out that the KDoc of withTransaction() has mentioned that it should use the same coroutineScope that receive by the suspending block to perform blocking database operation. So I guess it's the limitation of Room which let the usage of Store inside withTransaction() impossible.

[digitalbuddha]

I'm going to keep this issue open as we are currently rewriting some store internals for a Store5 major release. Let me think about how to solve this in a generic manner.