multi: asyncify, use rusqlite-based persistence

[torkelrogstad]

Currently struggling with the type check 😅

Need to be able to run async functions within with_mut of the wallet RwLockWriteGuardSome. Is that possible?

[Ash-L2L]

I'm not sure if this is the right approach. If you want persisting the wallet to be async, you will need to use an async DB connection. This will still block on commits

To get truly async IO, you would need to use something like sqlx , and manage tables manually. BDK does provide a schema https://docs.rs/bdk_wallet/latest/bdk_wallet/struct.ChangeSet.html#method.schema_v0

tokio-rusqlite is a drop-in replacement, but spawns a thread to handle a connection, whereas sqlx actually uses async IO AFAIK

Also, is there really a need for an internal mutex here? IMO it would make more sense to have the mutex external to the persister, so that a user has more control over locking behavior

[torkelrogstad]

To be completely honest I'm not sure I follow all the details on the conversations we're having on async, blocking, etc.

If I understand you correctly: we might end up with multiple different operations trying to access the DB at the same time, and they'll have to wait on one another because we only permit a single access to the DB connection concurrently. Is that correct? If so, I actually think this is fine, at least for this first version. I believe the SQLite persistor is going to be orders of magnitude quicker than the file_store approach we have currently. If we still see issues, we can go with a connection pool.

Re. the internal mutex: the reason for that is that I need to ensure that wallet::WalletInner is Sync. Is there some other way to accomplish that?

[torkelrogstad]

Replaced the mutexed rusqlite::Connection with a tokio_rusqlite implementation