Repository: bitcoin/bitcoin
File: src/validation.cpp (C++)

Code before:
        }
    }

    // Disconnect (descendants of) pindex, and mark them invalid.
    while (true) {
        if (m_chainman.m_interrupt) break;

        // Make sure the queue of validation callbacks doesn't grow unboundedly.
        if (m_chainman.m_options.signals) LimitValidationInterfaceQueue(*m_chainman.m_options.signals);

        LOCK(cs_main);
        // Lock for as long as disconnectpool is in scope to make sure MaybeUpdateMempoolForReorg is
        // called after DisconnectTip without unlocking in between
        LOCK(MempoolMutex());
        if (!m_chain.Contains(pindex)) break;
        pindex_was_in_chain = true;
        CBlockIndex *invalid_walk_tip = m_chain.Tip();

        // ActivateBestChain considers blocks already in m_chain
        // unconditionally valid already, so force disconnect away from it.
        DisconnectedBlockTransactions disconnectpool{MAX_DISCONNECTED_TX_POOL_BYTES};
        bool ret = DisconnectTip(state, &disconnectpool);
        // DisconnectTip will add transactions to disconnectpool.
        // Adjust the mempool to be consistent with the new tip, adding
        // transactions back to the mempool if disconnecting was successful,
        // and we're not doing a very deep invalidation (in which case
        // keeping the mempool up to date is probably futile anyway).
        MaybeUpdateMempoolForReorg(disconnectpool, /* fAddToMempool = */ (++disconnected <= 10) && ret);
        if (!ret) return false;
        assert(invalid_walk_tip->pprev == m_chain.Tip());

        // We immediately mark the disconnected blocks as invalid.
        // This prevents a case where pruned nodes may fail to invalidateblock
        // and be left unable to start as they have no tip candidates (as there
        // are no blocks that meet the "have data and are not invalid per
        // nStatus" criteria for inclusion in setBlockIndexCandidates).
        invalid_walk_tip->nStatus |= BLOCK_FAILED_VALID;
        m_blockman.m_dirty_blockindex.insert(invalid_walk_tip);
        setBlockIndexCandidates.erase(invalid_walk_tip);
        setBlockIndexCandidates.insert(invalid_walk_tip->pprev);
        if (invalid_walk_tip == to_mark_failed->pprev && (to_mark_failed->nStatus & BLOCK_FAILED_VALID)) {
            // We only want to mark the last disconnected block as BLOCK_FAILED_VALID; its children
            // need to be BLOCK_FAILED_CHILD instead.
            to_mark_failed->nStatus = (to_mark_failed->nStatus ^ BLOCK_FAILED_VALID) | BLOCK_FAILED_CHILD;
            m_blockman.m_dirty_blockindex.insert(to_mark_failed);
        }

        // Add any equal or more work headers to setBlockIndexCandidates
        auto candidate_it = candidate_blocks_by_work.lower_bound(invalid_walk_tip->pprev->nChainWork);
        while (candidate_it != candidate_blocks_by_work.end()) {
            if (!CBlockIndexWorkComparator()(candidate_it->second, invalid_walk_tip->pprev)) {

Review comment (suggestion):
I was surprised to see that `CheckBlockIndex()` is not a `const` method, which I think it should be. To help validate that this call is not having unexpected side-effects, I implemented the const-ness change and found no issues because of it: https://github.com/bitcoin/bitcoin/compare/master...stickies-v:bitcoin:2b68b3f8343fe6582cc2ecbc474f489a50bdeb11

~~I think this change would be good to have on master, but it doesn't have to be in this PR either, so if you'd rather no include it in this PR (it is a non-trivial change), I'm happy to open it as a separate PR?~~ _edit: opened https://github.com/bitcoin/bitcoin/pull/32364_

Code after:
    std::multimap<const arith_uint256, CBlockIndex*> highpow_outofchain_headers;

    {
        LOCK(cs_main);
        for (auto& entry : m_blockman.m_block_index) {
            CBlockIndex* candidate = &entry.second;
            // We don't need to put anything in our active chain into the
            // multimap, because those candidates will be found and considered
            // as we disconnect.
            // Instead, consider only non-active-chain blocks that score
            // at least as good with CBlockIndexWorkComparator as the new tip.
            if (!m_chain.Contains(candidate) &&
                !CBlockIndexWorkComparator()(candidate, pindex->pprev) &&
                !(candidate->nStatus & BLOCK_FAILED_MASK)) {
                highpow_outofchain_headers.insert({candidate->nChainWork, candidate});
            }
        }
    }

    // Disconnect (descendants of) pindex, and mark them invalid.
    while (true) {
        if (m_chainman.m_interrupt) break;

        // Make sure the queue of validation callbacks doesn't grow unboundedly.
        if (m_chainman.m_options.signals) LimitValidationInterfaceQueue(*m_chainman.m_options.signals);

        LOCK(cs_main);
        // Lock for as long as disconnectpool is in scope to make sure MaybeUpdateMempoolForReorg is
        // called after DisconnectTip without unlocking in between
        LOCK(MempoolMutex());
        if (!m_chain.Contains(pindex)) break;
        pindex_was_in_chain = true;
        CBlockIndex *invalid_walk_tip = m_chain.Tip();

        // ActivateBestChain considers blocks already in m_chain
        // unconditionally valid already, so force disconnect away from it.
        DisconnectedBlockTransactions disconnectpool{MAX_DISCONNECTED_TX_POOL_BYTES};
        bool ret = DisconnectTip(state, &disconnectpool);
        // DisconnectTip will add transactions to disconnectpool.
        // Adjust the mempool to be consistent with the new tip, adding
        // transactions back to the mempool if disconnecting was successful,
        // and we're not doing a very deep invalidation (in which case
        // keeping the mempool up to date is probably futile anyway).
        MaybeUpdateMempoolForReorg(disconnectpool, /* fAddToMempool = */ (++disconnected <= 10) && ret);
        if (!ret) return false;
        assert(invalid_walk_tip->pprev == m_chain.Tip());

        // We immediately mark the disconnected blocks as invalid.
        // This prevents a case where pruned nodes may fail to invalidateblock
        // and be left unable to start as they have no tip candidates (as there
        // are no blocks that meet the "have data and are not invalid per