Function sc_consensus_pow::import_queue

pub fn import_queue<B, Transaction, Algorithm>(
    block_import: BoxBlockImport<B, Transaction>, 
    justification_import: Option<BoxJustificationImport<B>>, 
    algorithm: Algorithm, 
    spawner: &impl SpawnEssentialNamed, 
    registry: Option<&Registry>
) -> Result<PowImportQueue<B, Transaction>, Error> where
    B: BlockT,
    Transaction: Send + Sync + 'static,
    Algorithm: PowAlgorithm<B> + Clone + Send + Sync + 'static,
    Algorithm::Difficulty: Send, 

Import queue for PoW engine.