miner.cpp

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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#include <node/miner.h>
 
#include <chain.h>
#include <chainparams.h>
#include <coins.h>
#include <common/args.h>
#include <consensus/amount.h>
#include <consensus/consensus.h>
#include <consensus/merkle.h>
#include <consensus/tx_verify.h>
#include <consensus/validation.h>
#include <deploymentstatus.h>
#include <logging.h>
#include <node/context.h>
#include <node/kernel_notifications.h>
#include <policy/feerate.h>
#include <policy/policy.h>
#include <pow.h>
#include <primitives/transaction.h>
#include <util/moneystr.h>
#include <util/signalinterrupt.h>
#include <util/time.h>
#include <validation.h>
 
#include <algorithm>
#include <utility>
 
namespace node {
 
int64_t GetMinimumTime(const CBlockIndex* pindexPrev, const int64_t difficulty_adjustment_interval)
{
    int64_t min_time{pindexPrev->GetMedianTimePast() + 1};
    // Height of block to be mined.
    const int height{pindexPrev->nHeight + 1};
    // Account for BIP94 timewarp rule on all networks. This makes future
    // activation safer.
    if (height % difficulty_adjustment_interval == 0) {
        min_time = std::max<int64_t>(min_time, pindexPrev->GetBlockTime() - MAX_TIMEWARP);
    }
    return min_time;
}
 
int64_t UpdateTime(CBlockHeader* pblock, const Consensus::Params& consensusParams, const CBlockIndex* pindexPrev)
{
    int64_t nOldTime = pblock->nTime;
    int64_t nNewTime{std::max<int64_t>(GetMinimumTime(pindexPrev, consensusParams.DifficultyAdjustmentInterval()),
                                       TicksSinceEpoch<std::chrono::seconds>(NodeClock::now()))};
 
    if (nOldTime < nNewTime) {
        pblock->nTime = nNewTime;
    }
 
    // Updating time can change work required on testnet:
    if (consensusParams.fPowAllowMinDifficultyBlocks) {
        pblock->nBits = GetNextWorkRequired(pindexPrev, pblock, consensusParams);
    }
 
    return nNewTime - nOldTime;
}
 
void RegenerateCommitments(CBlock& block, ChainstateManager& chainman)
{
    CMutableTransaction tx{*block.vtx.at(0)};
    tx.vout.erase(tx.vout.begin() + GetWitnessCommitmentIndex(block));
    block.vtx.at(0) = MakeTransactionRef(tx);
 
    const CBlockIndex* prev_block = WITH_LOCK(::cs_main, return chainman.m_blockman.LookupBlockIndex(block.hashPrevBlock));
    chainman.GenerateCoinbaseCommitment(block, prev_block);
 
    block.hashMerkleRoot = BlockMerkleRoot(block);
}
 
static BlockAssembler::Options ClampOptions(BlockAssembler::Options options)
{
    options.block_reserved_weight = std::clamp<size_t>(options.block_reserved_weight, MINIMUM_BLOCK_RESERVED_WEIGHT, MAX_BLOCK_WEIGHT);
    options.coinbase_output_max_additional_sigops = std::clamp<size_t>(options.coinbase_output_max_additional_sigops, 0, MAX_BLOCK_SIGOPS_COST);
    // Limit weight to between block_reserved_weight and MAX_BLOCK_WEIGHT for sanity:
    // block_reserved_weight can safely exceed -blockmaxweight, but the rest of the block template will be empty.
    options.nBlockMaxWeight = std::clamp<size_t>(options.nBlockMaxWeight, options.block_reserved_weight, MAX_BLOCK_WEIGHT);
    return options;
}
 
BlockAssembler::BlockAssembler(Chainstate& chainstate, const CTxMemPool* mempool, const Options& options)
    : chainparams{chainstate.m_chainman.GetParams()},
      m_mempool{options.use_mempool ? mempool : nullptr},
      m_chainstate{chainstate},
      m_options{ClampOptions(options)}
{
}
 
void ApplyArgsManOptions(const ArgsManager& args, BlockAssembler::Options& options)
{
    // Block resource limits
    options.nBlockMaxWeight = args.GetIntArg("-blockmaxweight", options.nBlockMaxWeight);
    if (const auto blockmintxfee{args.GetArg("-blockmintxfee")}) {
        if (const auto parsed{ParseMoney(*blockmintxfee)}) options.blockMinFeeRate = CFeeRate{*parsed};
    }
    options.print_modified_fee = args.GetBoolArg("-printpriority", options.print_modified_fee);
    options.block_reserved_weight = args.GetIntArg("-blockreservedweight", options.block_reserved_weight);
}
 
void BlockAssembler::resetBlock()
{
    inBlock.clear();
 
    // Reserve space for fixed-size block header, txs count, and coinbase tx.
    nBlockWeight = m_options.block_reserved_weight;
    nBlockSigOpsCost = m_options.coinbase_output_max_additional_sigops;
 
    // These counters do not include coinbase tx
    nBlockTx = 0;
    nFees = 0;
}
 
std::unique_ptr<CBlockTemplate> BlockAssembler::CreateNewBlock()
{
    const auto time_start{SteadyClock::now()};
 
    resetBlock();
 
    pblocktemplate.reset(new CBlockTemplate());
    CBlock* const pblock = &pblocktemplate->block; // pointer for convenience
 
    // Add dummy coinbase tx as first transaction. It is skipped by the
    // getblocktemplate RPC and mining interface consumers must not use it.
    pblock->vtx.emplace_back();
 
    LOCK(::cs_main);
    CBlockIndex* pindexPrev = m_chainstate.m_chain.Tip();
    assert(pindexPrev != nullptr);
    nHeight = pindexPrev->nHeight + 1;
 
    pblock->nVersion = m_chainstate.m_chainman.m_versionbitscache.ComputeBlockVersion(pindexPrev, chainparams.GetConsensus());
    // -regtest only: allow overriding block.nVersion with
    // -blockversion=N to test forking scenarios
    if (chainparams.MineBlocksOnDemand()) {
        pblock->nVersion = gArgs.GetIntArg("-blockversion", pblock->nVersion);
    }
 
    pblock->nTime = TicksSinceEpoch<std::chrono::seconds>(NodeClock::now());
    m_lock_time_cutoff = pindexPrev->GetMedianTimePast();
 
    int nPackagesSelected = 0;
    int nDescendantsUpdated = 0;
    if (m_mempool) {
        addPackageTxs(nPackagesSelected, nDescendantsUpdated);
    }
 
    const auto time_1{SteadyClock::now()};
 
    m_last_block_num_txs = nBlockTx;
    m_last_block_weight = nBlockWeight;
 
    // Create coinbase transaction.
    CMutableTransaction coinbaseTx;
    coinbaseTx.vin.resize(1);
    coinbaseTx.vin[0].prevout.SetNull();
    coinbaseTx.vin[0].nSequence = CTxIn::MAX_SEQUENCE_NONFINAL; // Make sure timelock is enforced.
    coinbaseTx.vout.resize(1);
    coinbaseTx.vout[0].scriptPubKey = m_options.coinbase_output_script;
    coinbaseTx.vout[0].nValue = nFees + GetBlockSubsidy(nHeight, chainparams.GetConsensus());
    coinbaseTx.vin[0].scriptSig = CScript() << nHeight << OP_0;
    Assert(nHeight > 0);
    coinbaseTx.nLockTime = static_cast<uint32_t>(nHeight - 1);
    pblock->vtx[0] = MakeTransactionRef(std::move(coinbaseTx));
    pblocktemplate->vchCoinbaseCommitment = m_chainstate.m_chainman.GenerateCoinbaseCommitment(*pblock, pindexPrev);
 
    LogPrintf("CreateNewBlock(): block weight: %u txs: %u fees: %ld sigops %d\n", GetBlockWeight(*pblock), nBlockTx, nFees, nBlockSigOpsCost);
 
    // Fill in header
    pblock->hashPrevBlock  = pindexPrev->GetBlockHash();
    UpdateTime(pblock, chainparams.GetConsensus(), pindexPrev);
    pblock->nBits          = GetNextWorkRequired(pindexPrev, pblock, chainparams.GetConsensus());
    pblock->nNonce         = 0;
 
    if (m_options.test_block_validity) {
        if (BlockValidationState state{TestBlockValidity(m_chainstate, *pblock, /*check_pow=*/false, /*check_merkle_root=*/false)}; !state.IsValid()) {
            throw std::runtime_error(strprintf("TestBlockValidity failed: %s", state.ToString()));
        }
    }
    const auto time_2{SteadyClock::now()};
 
    LogDebug(BCLog::BENCH, "CreateNewBlock() packages: %.2fms (%d packages, %d updated descendants), validity: %.2fms (total %.2fms)\n",
             Ticks<MillisecondsDouble>(time_1 - time_start), nPackagesSelected, nDescendantsUpdated,
             Ticks<MillisecondsDouble>(time_2 - time_1),
             Ticks<MillisecondsDouble>(time_2 - time_start));
 
    return std::move(pblocktemplate);
}
 
void BlockAssembler::onlyUnconfirmed(CTxMemPool::setEntries& testSet)
{
    for (CTxMemPool::setEntries::iterator iit = testSet.begin(); iit != testSet.end(); ) {
        // Only test txs not already in the block
        if (inBlock.count((*iit)->GetSharedTx()->GetHash())) {
            testSet.erase(iit++);
        } else {
            iit++;
        }
    }
}
 
bool BlockAssembler::TestPackage(uint64_t packageSize, int64_t packageSigOpsCost) const
{
    // TODO: switch to weight-based accounting for packages instead of vsize-based accounting.
    if (nBlockWeight + WITNESS_SCALE_FACTOR * packageSize >= m_options.nBlockMaxWeight) {
        return false;
    }
    if (nBlockSigOpsCost + packageSigOpsCost >= MAX_BLOCK_SIGOPS_COST) {
        return false;
    }
    return true;
}
 
// Perform transaction-level checks before adding to block:
// - transaction finality (locktime)
bool BlockAssembler::TestPackageTransactions(const CTxMemPool::setEntries& package) const
{
    for (CTxMemPool::txiter it : package) {
        if (!IsFinalTx(it->GetTx(), nHeight, m_lock_time_cutoff)) {
            return false;
        }
    }
    return true;
}
 
void BlockAssembler::AddToBlock(CTxMemPool::txiter iter)
{
    pblocktemplate->block.vtx.emplace_back(iter->GetSharedTx());
    pblocktemplate->vTxFees.push_back(iter->GetFee());
    pblocktemplate->vTxSigOpsCost.push_back(iter->GetSigOpCost());
    nBlockWeight += iter->GetTxWeight();
    ++nBlockTx;
    nBlockSigOpsCost += iter->GetSigOpCost();
    nFees += iter->GetFee();
    inBlock.insert(iter->GetSharedTx()->GetHash());
 
    if (m_options.print_modified_fee) {
        LogPrintf("fee rate %s txid %s\n",
                  CFeeRate(iter->GetModifiedFee(), iter->GetTxSize()).ToString(),
                  iter->GetTx().GetHash().ToString());
    }
}
 
static int UpdatePackagesForAdded(const CTxMemPool& mempool,
                                  const CTxMemPool::setEntries& alreadyAdded,
                                  indexed_modified_transaction_set& mapModifiedTx) EXCLUSIVE_LOCKS_REQUIRED(mempool.cs)
{
    AssertLockHeld(mempool.cs);
 
    int nDescendantsUpdated = 0;
    for (CTxMemPool::txiter it : alreadyAdded) {
        CTxMemPool::setEntries descendants;
        mempool.CalculateDescendants(it, descendants);
        // Insert all descendants (not yet in block) into the modified set
        for (CTxMemPool::txiter desc : descendants) {
            if (alreadyAdded.count(desc)) {
                continue;
            }
            ++nDescendantsUpdated;
            modtxiter mit = mapModifiedTx.find(desc);
            if (mit == mapModifiedTx.end()) {
                CTxMemPoolModifiedEntry modEntry(desc);
                mit = mapModifiedTx.insert(modEntry).first;
            }
            mapModifiedTx.modify(mit, update_for_parent_inclusion(it));
        }
    }
    return nDescendantsUpdated;
}
 
void BlockAssembler::SortForBlock(const CTxMemPool::setEntries& package, std::vector<CTxMemPool::txiter>& sortedEntries)
{
    // Sort package by ancestor count
    // If a transaction A depends on transaction B, then A's ancestor count
    // must be greater than B's.  So this is sufficient to validly order the
    // transactions for block inclusion.
    sortedEntries.clear();
    sortedEntries.insert(sortedEntries.begin(), package.begin(), package.end());
    std::sort(sortedEntries.begin(), sortedEntries.end(), CompareTxIterByAncestorCount());
}
 
// This transaction selection algorithm orders the mempool based
// on feerate of a transaction including all unconfirmed ancestors.
// Since we don't remove transactions from the mempool as we select them
// for block inclusion, we need an alternate method of updating the feerate
// of a transaction with its not-yet-selected ancestors as we go.
// This is accomplished by walking the in-mempool descendants of selected
// transactions and storing a temporary modified state in mapModifiedTxs.
// Each time through the loop, we compare the best transaction in
// mapModifiedTxs with the next transaction in the mempool to decide what
// transaction package to work on next.
void BlockAssembler::addPackageTxs(int& nPackagesSelected, int& nDescendantsUpdated)
{
    const auto& mempool{*Assert(m_mempool)};
    LOCK(mempool.cs);
 
    // mapModifiedTx will store sorted packages after they are modified
    // because some of their txs are already in the block
    indexed_modified_transaction_set mapModifiedTx;
    // Keep track of entries that failed inclusion, to avoid duplicate work
    std::set<Txid> failedTx;
 
    CTxMemPool::indexed_transaction_set::index<ancestor_score>::type::iterator mi = mempool.mapTx.get<ancestor_score>().begin();
    CTxMemPool::txiter iter;
 
    // Limit the number of attempts to add transactions to the block when it is
    // close to full; this is just a simple heuristic to finish quickly if the
    // mempool has a lot of entries.
    const int64_t MAX_CONSECUTIVE_FAILURES = 1000;
    constexpr int32_t BLOCK_FULL_ENOUGH_WEIGHT_DELTA = 4000;
    int64_t nConsecutiveFailed = 0;
 
    while (mi != mempool.mapTx.get<ancestor_score>().end() || !mapModifiedTx.empty()) {
        // First try to find a new transaction in mapTx to evaluate.
        //
        // Skip entries in mapTx that are already in a block or are present
        // in mapModifiedTx (which implies that the mapTx ancestor state is
        // stale due to ancestor inclusion in the block)
        // Also skip transactions that we've already failed to add. This can happen if
        // we consider a transaction in mapModifiedTx and it fails: we can then
        // potentially consider it again while walking mapTx.  It's currently
        // guaranteed to fail again, but as a belt-and-suspenders check we put it in
        // failedTx and avoid re-evaluation, since the re-evaluation would be using
        // cached size/sigops/fee values that are not actually correct.
        if (mi != mempool.mapTx.get<ancestor_score>().end()) {
            auto it = mempool.mapTx.project<0>(mi);
            assert(it != mempool.mapTx.end());
            if (mapModifiedTx.count(it) || inBlock.count(it->GetSharedTx()->GetHash()) || failedTx.count(it->GetSharedTx()->GetHash())) {
                ++mi;
                continue;
            }
        }
 
        // Now that mi is not stale, determine which transaction to evaluate:
        // the next entry from mapTx, or the best from mapModifiedTx?
        bool fUsingModified = false;
 
        modtxscoreiter modit = mapModifiedTx.get<ancestor_score>().begin();
        if (mi == mempool.mapTx.get<ancestor_score>().end()) {
            // We're out of entries in mapTx; use the entry from mapModifiedTx
            iter = modit->iter;
            fUsingModified = true;
        } else {
            // Try to compare the mapTx entry to the mapModifiedTx entry
            iter = mempool.mapTx.project<0>(mi);
            if (modit != mapModifiedTx.get<ancestor_score>().end() &&
                    CompareTxMemPoolEntryByAncestorFee()(*modit, CTxMemPoolModifiedEntry(iter))) {
                // The best entry in mapModifiedTx has higher score
                // than the one from mapTx.
                // Switch which transaction (package) to consider
                iter = modit->iter;
                fUsingModified = true;
            } else {
                // Either no entry in mapModifiedTx, or it's worse than mapTx.
                // Increment mi for the next loop iteration.
                ++mi;
            }
        }
 
        // We skip mapTx entries that are inBlock, and mapModifiedTx shouldn't
        // contain anything that is inBlock.
        assert(!inBlock.count(iter->GetSharedTx()->GetHash()));
 
        uint64_t packageSize = iter->GetSizeWithAncestors();
        CAmount packageFees = iter->GetModFeesWithAncestors();
        int64_t packageSigOpsCost = iter->GetSigOpCostWithAncestors();
        if (fUsingModified) {
            packageSize = modit->nSizeWithAncestors;
            packageFees = modit->nModFeesWithAncestors;
            packageSigOpsCost = modit->nSigOpCostWithAncestors;
        }
 
        if (packageFees < m_options.blockMinFeeRate.GetFee(packageSize)) {
            // Everything else we might consider has a lower fee rate
            return;
        }
 
        if (!TestPackage(packageSize, packageSigOpsCost)) {
            if (fUsingModified) {
                // Since we always look at the best entry in mapModifiedTx,
                // we must erase failed entries so that we can consider the
                // next best entry on the next loop iteration
                mapModifiedTx.get<ancestor_score>().erase(modit);
                failedTx.insert(iter->GetSharedTx()->GetHash());
            }
 
            ++nConsecutiveFailed;
 
            if (nConsecutiveFailed > MAX_CONSECUTIVE_FAILURES && nBlockWeight >
                    m_options.nBlockMaxWeight - BLOCK_FULL_ENOUGH_WEIGHT_DELTA) {
                // Give up if we're close to full and haven't succeeded in a while
                break;
            }
            continue;
        }
 
        auto ancestors{mempool.AssumeCalculateMemPoolAncestors(__func__, *iter, CTxMemPool::Limits::NoLimits(), /*fSearchForParents=*/false)};
 
        onlyUnconfirmed(ancestors);
        ancestors.insert(iter);
 
        // Test if all tx's are Final
        if (!TestPackageTransactions(ancestors)) {
            if (fUsingModified) {
                mapModifiedTx.get<ancestor_score>().erase(modit);
                failedTx.insert(iter->GetSharedTx()->GetHash());
            }
            continue;
        }
 
        // This transaction will make it in; reset the failed counter.
        nConsecutiveFailed = 0;
 
        // Package can be added. Sort the entries in a valid order.
        std::vector<CTxMemPool::txiter> sortedEntries;
        SortForBlock(ancestors, sortedEntries);
 
        for (size_t i = 0; i < sortedEntries.size(); ++i) {
            AddToBlock(sortedEntries[i]);
            // Erase from the modified set, if present
            mapModifiedTx.erase(sortedEntries[i]);
        }
 
        ++nPackagesSelected;
        pblocktemplate->m_package_feerates.emplace_back(packageFees, static_cast<int32_t>(packageSize));
 
        // Update transactions that depend on each of these
        nDescendantsUpdated += UpdatePackagesForAdded(mempool, ancestors, mapModifiedTx);
    }
}
 
void AddMerkleRootAndCoinbase(CBlock& block, CTransactionRef coinbase, uint32_t version, uint32_t timestamp, uint32_t nonce)
{
    if (block.vtx.size() == 0) {
        block.vtx.emplace_back(coinbase);
    } else {
        block.vtx[0] = coinbase;
    }
    block.nVersion = version;
    block.nTime = timestamp;
    block.nNonce = nonce;
    block.hashMerkleRoot = BlockMerkleRoot(block);
}
 
std::unique_ptr<CBlockTemplate> WaitAndCreateNewBlock(ChainstateManager& chainman,
                                                      KernelNotifications& kernel_notifications,
                                                      CTxMemPool* mempool,
                                                      const std::unique_ptr<CBlockTemplate>& block_template,
                                                      const BlockWaitOptions& options,
                                                      const BlockAssembler::Options& assemble_options)
{
    // Delay calculating the current template fees, just in case a new block
    // comes in before the next tick.
    CAmount current_fees = -1;
 
    // Alternate waiting for a new tip and checking if fees have risen.
    // The latter check is expensive so we only run it once per second.
    auto now{NodeClock::now()};
    const auto deadline = now + options.timeout;
    const MillisecondsDouble tick{1000};
    const bool allow_min_difficulty{chainman.GetParams().GetConsensus().fPowAllowMinDifficultyBlocks};
 
    do {
        bool tip_changed{false};
        {
            WAIT_LOCK(kernel_notifications.m_tip_block_mutex, lock);
            // Note that wait_until() checks the predicate before waiting
            kernel_notifications.m_tip_block_cv.wait_until(lock, std::min(now + tick, deadline), [&]() EXCLUSIVE_LOCKS_REQUIRED(kernel_notifications.m_tip_block_mutex) {
                AssertLockHeld(kernel_notifications.m_tip_block_mutex);
                const auto tip_block{kernel_notifications.TipBlock()};
                // We assume tip_block is set, because this is an instance
                // method on BlockTemplate and no template could have been
                // generated before a tip exists.
                tip_changed = Assume(tip_block) && tip_block != block_template->block.hashPrevBlock;
                return tip_changed || chainman.m_interrupt;
            });
        }
 
        if (chainman.m_interrupt) return nullptr;
        // At this point the tip changed, a full tick went by or we reached
        // the deadline.
 
        // Must release m_tip_block_mutex before locking cs_main, to avoid deadlocks.
        LOCK(::cs_main);
 
        // On test networks return a minimum difficulty block after 20 minutes
        if (!tip_changed && allow_min_difficulty) {
            const NodeClock::time_point tip_time{std::chrono::seconds{chainman.ActiveChain().Tip()->GetBlockTime()}};
            if (now > tip_time + 20min) {
                tip_changed = true;
            }
        }
 
        if (options.fee_threshold < MAX_MONEY || tip_changed) {
            auto new_tmpl{BlockAssembler{
                chainman.ActiveChainstate(),
                mempool,
                assemble_options}
                              .CreateNewBlock()};
 
            // If the tip changed, return the new template regardless of its fees.
            if (tip_changed) return new_tmpl;
 
            // Calculate the original template total fees if we haven't already
            if (current_fees == -1) {
                current_fees = 0;
                for (CAmount fee : block_template->vTxFees) {
                    current_fees += fee;
                }
            }
 
            CAmount new_fees = 0;
            for (CAmount fee : new_tmpl->vTxFees) {
                new_fees += fee;
                Assume(options.fee_threshold != MAX_MONEY);
                if (new_fees >= current_fees + options.fee_threshold) return new_tmpl;
            }
        }
 
        now = NodeClock::now();
    } while (now < deadline);
 
    return nullptr;
}
 
std::optional<BlockRef> GetTip(ChainstateManager& chainman)
{
    LOCK(::cs_main);
    CBlockIndex* tip{chainman.ActiveChain().Tip()};
    if (!tip) return {};
    return BlockRef{tip->GetBlockHash(), tip->nHeight};
}
 
std::optional<BlockRef> WaitTipChanged(ChainstateManager& chainman, KernelNotifications& kernel_notifications, const uint256& current_tip, MillisecondsDouble& timeout)
{
    Assume(timeout >= 0ms); // No internal callers should use a negative timeout
    if (timeout < 0ms) timeout = 0ms;
    if (timeout > std::chrono::years{100}) timeout = std::chrono::years{100}; // Upper bound to avoid UB in std::chrono
    auto deadline{std::chrono::steady_clock::now() + timeout};
    {
        WAIT_LOCK(kernel_notifications.m_tip_block_mutex, lock);
        // For callers convenience, wait longer than the provided timeout
        // during startup for the tip to be non-null. That way this function
        // always returns valid tip information when possible and only
        // returns null when shutting down, not when timing out.
        kernel_notifications.m_tip_block_cv.wait(lock, [&]() EXCLUSIVE_LOCKS_REQUIRED(kernel_notifications.m_tip_block_mutex) {
            return kernel_notifications.TipBlock() || chainman.m_interrupt;
        });
        if (chainman.m_interrupt) return {};
        // At this point TipBlock is set, so continue to wait until it is
        // different then `current_tip` provided by caller.
        kernel_notifications.m_tip_block_cv.wait_until(lock, deadline, [&]() EXCLUSIVE_LOCKS_REQUIRED(kernel_notifications.m_tip_block_mutex) {
            return Assume(kernel_notifications.TipBlock()) != current_tip || chainman.m_interrupt;
        });
    }
    if (chainman.m_interrupt) return {};
 
    // Must release m_tip_block_mutex before getTip() locks cs_main, to
    // avoid deadlocks.
    return GetTip(chainman);
}
} // namespace node