Distributed locks

Corvis does not include distributed locks (mutual exclusion across several instances of the application).

Alternative

• Within a single process, a tokio::sync::Mutex kept in a provider is enough.
• Across instances that share a PostgreSQL database, you can use Postgres advisory locks with corvis-orm raw SQL, inside a transaction so the lock is released when it ends:

use corvis_orm::{OrmError, sql};

db._transaction(|tx| async move {
    let rows = tx._query_raw(sql!("SELECT pg_try_advisory_xact_lock({key}) AS locked")).await?;
    // If `locked` is false, another instance holds the lock.
    Ok::<_, OrmError>(rows)
}).await?;

This is useful, for example, to make a #[cron] task run on a single instance (see Task scheduling).