Merge bitcoin/bitcoin#24515: Only load BlockMan in BlockMan member functions

f865cf8ded2b2fbc82a6fbc41226d991909a6880 Add and use BlockManager::GetAllBlockIndices (Carl Dong)
28ba0313eac37e4a900b7e97af7169ce999c4024 Add and use CBlockIndexHeightOnlyComparator (Carl Dong)
12eb05df63f930969115af6dc66e2e5d02f2a517 move-only: Move CBlockIndexWorkComparator to blockstorage (Carl Dong)
c600ee38168a460d3026eae0e289c976194aad14 Only load BlockMan in BlockMan member functions (Carl Dong)
42e56d9b188f97c077ed2269e24acc0be35ece17 style-only: No need for std::pair for vSortedByHeight (Carl Dong)
3bbb6fea051f4e19bd2448e401a6c4e9b4cc7a41 style-only: Various blockstorage.cpp cleanups (Carl Dong)
5be9ee3c54dcb396ff52fc8c8b7e4e6e39ec4a3b refactor: more const annotations for uses of CBlockIndex* (Anthony Towns)

Pull request description:

  The only important commit is "Only load BlockMan in BlockMan member functions", everything else is all just small style changes.

  Here's the commit message, reproduced:
  ```
  This commit effectively splits the "load block index itself" logic from
  "derive Chainstate variables from loaded block index" logic.

  This means that BlockManager::LoadBlockIndex{,DB} will only load what's
  relevant to the BlockManager.
  ```

ACKs for top commit:
  ajtowns:
    ACK f865cf8ded2b2fbc82a6fbc41226d991909a6880 ; code review only
  MarcoFalke:
    review ACK f865cf8ded2b2fbc82a6fbc41226d991909a6880 🗂

Tree-SHA512: 7b204d782834e06fd7329d022e2ae860181b4e8105c33bfb928539a4ec24161dc7438a9c4d4ee279dcad77de310c160b997bb8aa18923243d0fd55ccf4ad7c3a

4 files changed, 61 insertions, 86 deletions

diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index 7392830261..763fd29744 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -28,10 +28,45 @@ bool fHavePruned = false;
 bool fPruneMode = false;
 uint64_t nPruneTarget = 0;
 
+bool CBlockIndexWorkComparator::operator()(const CBlockIndex* pa, const CBlockIndex* pb) const
+{
+    // First sort by most total work, ...
+    if (pa->nChainWork > pb->nChainWork) return false;
+    if (pa->nChainWork < pb->nChainWork) return true;
+
+    // ... then by earliest time received, ...
+    if (pa->nSequenceId < pb->nSequenceId) return false;
+    if (pa->nSequenceId > pb->nSequenceId) return true;
+
+    // Use pointer address as tie breaker (should only happen with blocks
+    // loaded from disk, as those all have id 0).
+    if (pa < pb) return false;
+    if (pa > pb) return true;
+
+    // Identical blocks.
+    return false;
+}
+
+bool CBlockIndexHeightOnlyComparator::operator()(const CBlockIndex* pa, const CBlockIndex* pb) const
+{
+    return pa->nHeight < pb->nHeight;
+}
+
 static FILE* OpenUndoFile(const FlatFilePos& pos, bool fReadOnly = false);
 static FlatFileSeq BlockFileSeq();
 static FlatFileSeq UndoFileSeq();
 
+std::vector<CBlockIndex*> BlockManager::GetAllBlockIndices()
+{
+    AssertLockHeld(cs_main);
+    std::vector<CBlockIndex*> rv;
+    rv.reserve(m_block_index.size());
+    for (auto& [_, block_index] : m_block_index) {
+        rv.push_back(&block_index);
+    }
+    return rv;
+}
+
 CBlockIndex* BlockManager::LookupBlockIndex(const uint256& hash)
 {
     AssertLockHeld(cs_main);
@@ -203,8 +238,7 @@ CBlockIndex* BlockManager::InsertBlockIndex(const uint256& hash)
         return nullptr;
     }
 
-    // Return existing or create new
-    auto [mi, inserted] = m_block_index.try_emplace(hash);
+    const auto [mi, inserted]{m_block_index.try_emplace(hash)};
     CBlockIndex* pindex = &(*mi).second;
     if (inserted) {
         pindex->phashBlock = &((*mi).first);
@@ -212,46 +246,19 @@ CBlockIndex* BlockManager::InsertBlockIndex(const uint256& hash)
     return pindex;
 }
 
-bool BlockManager::LoadBlockIndex(
-    const Consensus::Params& consensus_params,
-    ChainstateManager& chainman)
+bool BlockManager::LoadBlockIndex(const Consensus::Params& consensus_params)
 {
     if (!m_block_tree_db->LoadBlockIndexGuts(consensus_params, [this](const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main) { return this->InsertBlockIndex(hash); })) {
         return false;
     }
 
     // Calculate nChainWork
-    std::vector<std::pair<int, CBlockIndex*>> vSortedByHeight;
-    vSortedByHeight.reserve(m_block_index.size());
-    for (auto& [_, block_index] : m_block_index) {
-        CBlockIndex* pindex = &block_index;
-        vSortedByHeight.push_back(std::make_pair(pindex->nHeight, pindex));
-    }
-    sort(vSortedByHeight.begin(), vSortedByHeight.end());
-
-    // Find start of assumed-valid region.
-    int first_assumed_valid_height = std::numeric_limits<int>::max();
-
-    for (const auto& [height, block] : vSortedByHeight) {
-        if (block->IsAssumedValid()) {
-            auto chainstates = chainman.GetAll();
-
-            // If we encounter an assumed-valid block index entry, ensure that we have
-            // one chainstate that tolerates assumed-valid entries and another that does
-            // not (i.e. the background validation chainstate), since assumed-valid
-            // entries should always be pending validation by a fully-validated chainstate.
-            auto any_chain = [&](auto fnc) { return std::any_of(chainstates.cbegin(), chainstates.cend(), fnc); };
-            assert(any_chain([](auto chainstate) { return chainstate->reliesOnAssumedValid(); }));
-            assert(any_chain([](auto chainstate) { return !chainstate->reliesOnAssumedValid(); }));
-
-            first_assumed_valid_height = height;
-            break;
-        }
-    }
+    std::vector<CBlockIndex*> vSortedByHeight{GetAllBlockIndices()};
+    std::sort(vSortedByHeight.begin(), vSortedByHeight.end(),
+              CBlockIndexHeightOnlyComparator());
 
-    for (const std::pair<int, CBlockIndex*>& item : vSortedByHeight) {
+    for (CBlockIndex* pindex : vSortedByHeight) {
         if (ShutdownRequested()) return false;
-        CBlockIndex* pindex = item.second;
         pindex->nChainWork = (pindex->pprev ? pindex->pprev->nChainWork : 0) + GetBlockProof(*pindex);
         pindex->nTimeMax = (pindex->pprev ? std::max(pindex->pprev->nTimeMax, pindex->nTime) : pindex->nTime);
 
@@ -275,43 +282,6 @@ bool BlockManager::LoadBlockIndex(
             pindex->nStatus |= BLOCK_FAILED_CHILD;
             m_dirty_blockindex.insert(pindex);
         }
-        if (pindex->IsAssumedValid() ||
-                (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) &&
-                 (pindex->HaveTxsDownloaded() || pindex->pprev == nullptr))) {
-
-            // Fill each chainstate's block candidate set. Only add assumed-valid
-            // blocks to the tip candidate set if the chainstate is allowed to rely on
-            // assumed-valid blocks.
-            //
-            // If all setBlockIndexCandidates contained the assumed-valid blocks, the
-            // background chainstate's ActivateBestChain() call would add assumed-valid
-            // blocks to the chain (based on how FindMostWorkChain() works). Obviously
-            // we don't want this since the purpose of the background validation chain
-            // is to validate assued-valid blocks.
-            //
-            // Note: This is considering all blocks whose height is greater or equal to
-            // the first assumed-valid block to be assumed-valid blocks, and excluding
-            // them from the background chainstate's setBlockIndexCandidates set. This
-            // does mean that some blocks which are not technically assumed-valid
-            // (later blocks on a fork beginning before the first assumed-valid block)
-            // might not get added to the background chainstate, but this is ok,
-            // because they will still be attached to the active chainstate if they
-            // actually contain more work.
-            //
-            // Instead of this height-based approach, an earlier attempt was made at
-            // detecting "holistically" whether the block index under consideration
-            // relied on an assumed-valid ancestor, but this proved to be too slow to
-            // be practical.
-            for (CChainState* chainstate : chainman.GetAll()) {
-                if (chainstate->reliesOnAssumedValid() ||
-                        pindex->nHeight < first_assumed_valid_height) {
-                    chainstate->setBlockIndexCandidates.insert(pindex);
-                }
-            }
-        }
-        if (pindex->nStatus & BLOCK_FAILED_MASK && (!chainman.m_best_invalid || pindex->nChainWork > chainman.m_best_invalid->nChainWork)) {
-            chainman.m_best_invalid = pindex;
-        }
         if (pindex->pprev) {
             pindex->BuildSkip();
         }
@@ -355,9 +325,9 @@ bool BlockManager::WriteBlockIndexDB()
     return true;
 }
 
-bool BlockManager::LoadBlockIndexDB(ChainstateManager& chainman)
+bool BlockManager::LoadBlockIndexDB()
 {
-    if (!LoadBlockIndex(::Params().GetConsensus(), chainman)) {
+    if (!LoadBlockIndex(::Params().GetConsensus())) {
         return false;
     }
 
@@ -382,9 +352,8 @@ bool BlockManager::LoadBlockIndexDB(ChainstateManager& chainman)
     LogPrintf("Checking all blk files are present...\n");
     std::set<int> setBlkDataFiles;
     for (const auto& [_, block_index] : m_block_index) {
-        const CBlockIndex* pindex = &block_index;
-        if (pindex->nStatus & BLOCK_HAVE_DATA) {
-            setBlkDataFiles.insert(pindex->nFile);
+        if (block_index.nStatus & BLOCK_HAVE_DATA) {
+            setBlkDataFiles.insert(block_index.nFile);
         }
     }
     for (std::set<int>::iterator it = setBlkDataFiles.begin(); it != setBlkDataFiles.end(); it++) {
@@ -408,13 +377,13 @@ bool BlockManager::LoadBlockIndexDB(ChainstateManager& chainman)
     return true;
 }
 
-CBlockIndex* BlockManager::GetLastCheckpoint(const CCheckpointData& data)
+const CBlockIndex* BlockManager::GetLastCheckpoint(const CCheckpointData& data)
 {
     const MapCheckpoints& checkpoints = data.mapCheckpoints;
 
     for (const MapCheckpoints::value_type& i : reverse_iterate(checkpoints)) {
         const uint256& hash = i.second;
-        CBlockIndex* pindex = LookupBlockIndex(hash);
+        const CBlockIndex* pindex = LookupBlockIndex(hash);
         if (pindex) {
             return pindex;
         }
diff --git a/src/node/blockstorage.h b/src/node/blockstorage.h
index 12224f7a5d..a051e90808 100644
--- a/src/node/blockstorage.h
+++ b/src/node/blockstorage.h
@@ -62,6 +62,11 @@ struct CBlockIndexWorkComparator {
     bool operator()(const CBlockIndex* pa, const CBlockIndex* pb) const;
 };
 
+struct CBlockIndexHeightOnlyComparator {
+    /* Only compares the height of two block indices, doesn't try to tie-break */
+    bool operator()(const CBlockIndex* pa, const CBlockIndex* pb) const;
+};
+
 /**
  * Maintains a tree of blocks (stored in `m_block_index`) which is consulted
  * to determine where the most-work tip is.
@@ -118,6 +123,8 @@ private:
 public:
     BlockMap m_block_index GUARDED_BY(cs_main);
 
+    std::vector<CBlockIndex*> GetAllBlockIndices() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+
     /**
      * All pairs A->B, where A (or one of its ancestors) misses transactions, but B has transactions.
      * Pruned nodes may have entries where B is missing data.
@@ -127,16 +134,15 @@ public:
     std::unique_ptr<CBlockTreeDB> m_block_tree_db GUARDED_BY(::cs_main);
 
     bool WriteBlockIndexDB() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
-    bool LoadBlockIndexDB(ChainstateManager& chainman) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+    bool LoadBlockIndexDB() EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     /**
      * Load the blocktree off disk and into memory. Populate certain metadata
      * per index entry (nStatus, nChainWork, nTimeMax, etc.) as well as peripheral
      * collections like m_dirty_blockindex.
      */
-    bool LoadBlockIndex(
-        const Consensus::Params& consensus_params,
-        ChainstateManager& chainman) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    bool LoadBlockIndex(const Consensus::Params& consensus_params)
+        EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     /** Clear all data members. */
     void Unload() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
@@ -163,7 +169,7 @@ public:
     uint64_t CalculateCurrentUsage();
 
     //! Returns last CBlockIndex* that is a checkpoint
-    CBlockIndex* GetLastCheckpoint(const CCheckpointData& data) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    const CBlockIndex* GetLastCheckpoint(const CCheckpointData& data) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     ~BlockManager()
     {
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index cb063ae9f8..74d53d2062 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -490,7 +490,7 @@ public:
     {
         LOCK(cs_main);
         const CChainState& active = Assert(m_node.chainman)->ActiveChainstate();
-        if (CBlockIndex* fork = active.FindForkInGlobalIndex(locator)) {
+        if (const CBlockIndex* fork = active.FindForkInGlobalIndex(locator)) {
             return fork->nHeight;
         }
         return std::nullopt;
@@ -557,7 +557,7 @@ public:
         // used to limit the range, and passing min_height that's too low or
         // max_height that's too high will not crash or change the result.
         LOCK(::cs_main);
-        if (CBlockIndex* block = chainman().m_blockman.LookupBlockIndex(block_hash)) {
+        if (const CBlockIndex* block = chainman().m_blockman.LookupBlockIndex(block_hash)) {
             if (max_height && block->nHeight >= *max_height) block = block->GetAncestor(*max_height);
             for (; block->nStatus & BLOCK_HAVE_DATA; block = block->pprev) {
                 // Check pprev to not segfault if min_height is too low
diff --git a/src/node/miner.cpp b/src/node/miner.cpp
index 54afbb8839..917df91933 100644
--- a/src/node/miner.cpp
+++ b/src/node/miner.cpp
@@ -50,7 +50,7 @@ void RegenerateCommitments(CBlock& block, ChainstateManager& chainman)
     tx.vout.erase(tx.vout.begin() + GetWitnessCommitmentIndex(block));
     block.vtx.at(0) = MakeTransactionRef(tx);
 
-    CBlockIndex* prev_block = WITH_LOCK(::cs_main, return chainman.m_blockman.LookupBlockIndex(block.hashPrevBlock));
+    const CBlockIndex* prev_block = WITH_LOCK(::cs_main, return chainman.m_blockman.LookupBlockIndex(block.hashPrevBlock));
     GenerateCoinbaseCommitment(block, prev_block, Params().GetConsensus());
 
     block.hashMerkleRoot = BlockMerkleRoot(block);