Function maintain_transaction_pool_future 

pub fn maintain_transaction_pool_future<N, Client, P, St, Tasks>(
    client: Client,
    pool: P,
    events: St,
    task_spawner: Tasks,
    config: MaintainPoolConfig,
) -> Pin<Box<dyn Future<Output = ()> + Send>>
where
    N: NodePrimitives,
    Client: StateProviderFactory + BlockReaderIdExt<Header = <N as NodePrimitives>::BlockHeader> + ChainSpecProvider + Clone + 'static,
    <Client as ChainSpecProvider>::ChainSpec: EthChainSpec<Header = <N as NodePrimitives>::BlockHeader>,
    P: TransactionPoolExt + 'static,
    <P as TransactionPool>::Transaction: PoolTransaction<Consensus = <N as NodePrimitives>::SignedTx>,
    St: Stream<Item = CanonStateNotification<N>> + Send + Unpin + 'static,
    Tasks: TaskSpawner + 'static,

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