Function run_in_isolated_tx 

pub async fn run_in_isolated_tx<F, Fut, T>(
    pool: &PgPool,
    isolation: TransactionIsolation,
    body: F,
) -> Result<T, CoolError>
where
    F: FnMut(Transaction<'static, Postgres>) -> Fut,
    Fut: Future<Output = Result<(T, Transaction<'static, Postgres>), CoolError>>,

Begin a transaction at the requested isolation level, run body against the live transaction, and commit. On 40001 (serialization_failure) or 40P01 (deadlock_detected) the transaction is rolled back and the body runs again, up to MAX_RETRIES_DEFAULT times. Other errors propagate immediately.

body receives a mutable transaction reference; it should run all of its SQL through that reference so the writes participate in the same transaction.