There are some potential feefilter cleanups mentioned and motivated in comment https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-805808485 . If you address the locking one, please be careful and make sure that `round()` is only called under a lock. See https://github.com/bitcoin/bitcoin/pull/21509#issuecomment-807992199

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* Bitcoin Core P2P design
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{
public:
    PeerManagerImpl(const CChainParams& chainparams, CConnman& connman, CAddrMan& addrman,
                    BanMan* banman, CScheduler& scheduler, ChainstateManager& chainman,
                    CTxMemPool& pool, bool ignore_incoming_txs);
    
    void BlockConnected(const std::shared_ptr<const CBlock>& pblock, const CBlockIndex* pindexConnected) override;
    void BlockDisconnected(const std::shared_ptr<const CBlock> &block, const CBlockIndex* pindex) override;
    void UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) override;
    void BlockChecked(const CBlock& block, const BlockValidationState& state) override;
    void NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr<const CBlock>& pblock) override;
    
    void InitializeNode(CNode* pnode) override;
    void FinalizeNode(const CNode& node) override;
    bool ProcessMessages(CNode* pfrom, std::atomic<bool>& interrupt) override;
    bool SendMessages(CNode* pto) override EXCLUSIVE_LOCKS_REQUIRED(pto->cs_sendProcessing);
    
    void CheckForStaleTipAndEvictPeers() override;
    bool GetNodeStateStats(NodeId nodeid, CNodeStateStats& stats) const override;
    bool IgnoresIncomingTxs() override { return m_ignore_incoming_txs; }
    void SendPings() override;
    void RelayTransaction(const uint256& txid, const uint256& wtxid) override;
    void SetBestHeight(int height) override { m_best_height = height; };