Function maintain_transaction_pool_conditional_future 

pub fn maintain_transaction_pool_conditional_future<N, Pool, St>(
    pool: Pool,
    events: St,
) -> BoxFuture<'static, ()>
where
    N: NodePrimitives,
    Pool: TransactionPool + 'static,
    Pool::Transaction: MaybeConditionalTransaction,
    St: Stream<Item = CanonStateNotification<N>> + Send + Unpin + 'static,

Returns a spawnable future for maintaining the state of the conditional txs in the transaction pool.