chainActive setBlockIndexCandidates 중에서 pow선택하기

초등생 도미넌스 (차트를 크게보려면 그림위에서 마우스 우측버튼 "새탭에서 이미지 열기"선택합니다)

/**
 * Return the tip of the chain with the most work in it, that isn't known to be
 * invalid (it's however far from certain to be valid).
 */
static CBlockIndex *FindMostWorkChain() {
    do {
        CBlockIndex *pindexNew = nullptr;

        // Find the best candidate header.
        {
            std::set<CBlockIndex *, CBlockIndexWorkComparator>::reverse_iterator
                it = setBlockIndexCandidates.rbegin();
            if (it == setBlockIndexCandidates.rend()) return nullptr;
            pindexNew = *it;
        }

        // Check whether all blocks on the path between the currently active
        // chain and the candidate are valid. Just going until the active chain
        // is an optimization, as we know all blocks in it are valid already.
        CBlockIndex *pindexTest = pindexNew;
        bool fInvalidAncestor = false;
        while (pindexTest && !chainActive.Contains(pindexTest)) {
            assert(pindexTest->nChainTx || pindexTest->nHeight == 0);

            // Pruned nodes may have entries in setBlockIndexCandidates for
            // which block files have been deleted. Remove those as candidates
            // for the most work chain if we come across them; we can't switch
            // to a chain unless we have all the non-active-chain parent blocks.
            bool fFailedChain = pindexTest->nStatus & BLOCK_FAILED_MASK;
            bool fMissingData = !(pindexTest->nStatus & BLOCK_HAVE_DATA);
            if (fFailedChain || fMissingData) {
                // Candidate chain is not usable (either invalid or missing
                // data)
                if (fFailedChain &&
                    (pindexBestInvalid == nullptr ||
                     pindexNew->nChainWork > pindexBestInvalid->nChainWork))
                    pindexBestInvalid = pindexNew;
                CBlockIndex *pindexFailed = pindexNew;
                // Remove the entire chain from the set.
                while (pindexTest != pindexFailed) {
                    if (fFailedChain) {
                        pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
                    } else if (fMissingData) {
                        // If we're missing data, then add back to
                        // mapBlocksUnlinked, so that if the block arrives in
                        // the future we can try adding to
                        // setBlockIndexCandidates again.
                        mapBlocksUnlinked.insert(
                            std::make_pair(pindexFailed->pprev, pindexFailed));
                    }
                    setBlockIndexCandidates.erase(pindexFailed);
                    pindexFailed = pindexFailed->pprev;
                }
                setBlockIndexCandidates.erase(pindexTest);
                fInvalidAncestor = true;
                break;
            }
            pindexTest = pindexTest->pprev;
        }
        if (!fInvalidAncestor) return pindexNew;
    } while (true);
}

chainActive 가 현재 블록체인중에서 메인 체인이고, 항상 후보가 있을 수 있는데 이건 setBlockIndexCandidates 에 저장되어 있다. 항상 위 두 체인을 비교해서 메인 블록을 선택한다.