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doc: Improve comments describing setBlockIndexCandidates checks

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The checks are changing slightly in the next commit, so try to explains the
ones that exist to avoid confusion
(https://github.com/bitcoin/bitcoin/pull/29370#discussion_r1499519079)
This commit is contained in:
Ryan Ofsky 2024-02-02 10:59:24 -05:00
parent 0fd915ee6b
commit 9b97d5bbf9
1 changed files with 32 additions and 9 deletions
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41
src/validation.cpp
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@ -5126,19 +5126,42 @@ void ChainstateManager::CheckBlockIndex()
// Chainstate-specific checks on setBlockIndexCandidates
for (auto c : GetAll()) {
if (c->m_chain.Tip() == nullptr) continue;
// Two main factors determine whether pindex is a candidate in
// setBlockIndexCandidates:
//
// - If pindex has less work than the chain tip, it should not be a
// candidate, and this will be asserted below. Otherwise it is a
// potential candidate.
//
// - If pindex or one of its parent blocks never downloaded
// transactions (pindexFirstNeverProcessed is non-null), it should
// not be a candidate, and this will be asserted below. Otherwise
// it is a potential candidate.
if (!CBlockIndexWorkComparator()(pindex, c->m_chain.Tip()) && pindexFirstNeverProcessed == nullptr) {
// If pindex was detected as invalid (pindexFirstInvalid is
// non-null), it is not required to be in
// setBlockIndexCandidates.
if (pindexFirstInvalid == nullptr) {
const bool is_active = c == &ActiveChainstate();
// If this block sorts at least as good as the current tip and
// is valid and we have all data for its parents, it must be in
// setBlockIndexCandidates. m_chain.Tip() must also be there
// even if some data has been pruned.
// If pindex and all its parents downloaded transactions,
// and the transactions were not pruned (pindexFirstMissing
// is null), it is a potential candidate. The check
// excludes pruned blocks, because if any blocks were
// pruned between pindex the current chain tip, pindex will
// only temporarily be added to setBlockIndexCandidates,
// before being moved to m_blocks_unlinked. This check
// could be improved to verify that if all blocks between
// the chain tip and pindex have data, pindex must be a
// candidate.
//
// If pindex is the chain tip, it also is a potential
// candidate.
if ((pindexFirstMissing == nullptr || pindex == c->m_chain.Tip())) {
// The active chainstate should always have this block
// as a candidate, but a background chainstate should
// only have it if it is an ancestor of the snapshot base.
if (is_active || GetSnapshotBaseBlock()->GetAncestor(pindex->nHeight) == pindex) {
// If this chainstate is the active chainstate, pindex
// must be in setBlockIndexCandidates. Otherwise, this
// chainstate is a background validation chainstate, and
// pindex only needs to be added if it is an ancestor of
// the snapshot that is being validated.
if (c == &ActiveChainstate() || GetSnapshotBaseBlock()->GetAncestor(pindex->nHeight) == pindex) {
assert(c->setBlockIndexCandidates.count(pindex));
}
}