Method update_hmap

code/chapter09/blockchain/blockchain8/core/src/blockchain.rs:71–75

(hmap: &mut Mutex<HashMap<String, Block>>, block: Block)

    }

    fn update_hmap(hmap: &mut Mutex<HashMap<String, Block>>, block: Block) {
        let mut hmap = hmap.lock().unwrap();
        let hash = block.hash.clone();
        hmap.insert(hash, block);
    }

    fn write_block(db: &mut Database<BKey>, block: &Block) {
        let header_ser = serialize(&(block.header));