blockstorage: Make m_block_index own CBlockIndex's

Instead of having CBlockIndex's live on the heap, which requires manual
memory management, have them be owned by m_block_index. This means that
they will live and die with BlockManager.

A change to BlockManager::LookupBlockIndex:
- Previously, it was a const member function returning a non-const CBlockIndex*
- Now, there's are const and non-const versions of
  BlockManager::LookupBlockIndex returning a CBlockIndex with the same
  const-ness as the member function:
    (e.g. const CBlockIndex* LookupBlockIndex(...) const)

See next commit for some weirdness that this eliminates.

The range based for-loops are modernize (using auto + destructuring) in
a future commit.

5 files changed, 58 insertions, 47 deletions

diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index 8a99130fd0..a13c1a9956 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -32,11 +32,18 @@ static FILE* OpenUndoFile(const FlatFilePos& pos, bool fReadOnly = false);
 static FlatFileSeq BlockFileSeq();
 static FlatFileSeq UndoFileSeq();
 
-CBlockIndex* BlockManager::LookupBlockIndex(const uint256& hash) const
+CBlockIndex* BlockManager::LookupBlockIndex(const uint256& hash)
+{
+    AssertLockHeld(cs_main);
+    BlockMap::iterator it = m_block_index.find(hash);
+    return it == m_block_index.end() ? nullptr : &it->second;
+}
+
+const CBlockIndex* BlockManager::LookupBlockIndex(const uint256& hash) const
 {
     AssertLockHeld(cs_main);
     BlockMap::const_iterator it = m_block_index.find(hash);
-    return it == m_block_index.end() ? nullptr : it->second;
+    return it == m_block_index.end() ? nullptr : &it->second;
 }
 
 CBlockIndex* BlockManager::AddToBlockIndex(const CBlockHeader& block)
@@ -47,20 +54,22 @@ CBlockIndex* BlockManager::AddToBlockIndex(const CBlockHeader& block)
     uint256 hash = block.GetHash();
     BlockMap::iterator it = m_block_index.find(hash);
     if (it != m_block_index.end()) {
-        return it->second;
+        return &it->second;
     }
 
     // Construct new block index object
-    CBlockIndex* pindexNew = new CBlockIndex(block);
+    CBlockIndex new_index{block};
     // We assign the sequence id to blocks only when the full data is available,
     // to avoid miners withholding blocks but broadcasting headers, to get a
     // competitive advantage.
-    pindexNew->nSequenceId = 0;
-    BlockMap::iterator mi = m_block_index.insert(std::make_pair(hash, pindexNew)).first;
+    new_index.nSequenceId = 0;
+    BlockMap::iterator mi = m_block_index.insert(std::make_pair(hash, std::move(new_index))).first;
+
+    CBlockIndex* pindexNew = &(*mi).second;
     pindexNew->phashBlock = &((*mi).first);
     BlockMap::iterator miPrev = m_block_index.find(block.hashPrevBlock);
     if (miPrev != m_block_index.end()) {
-        pindexNew->pprev = (*miPrev).second;
+        pindexNew->pprev = &(*miPrev).second;
         pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
         pindexNew->BuildSkip();
     }
@@ -80,8 +89,8 @@ void BlockManager::PruneOneBlockFile(const int fileNumber)
     AssertLockHeld(cs_main);
     LOCK(cs_LastBlockFile);
 
-    for (const auto& entry : m_block_index) {
-        CBlockIndex* pindex = entry.second;
+    for (auto& entry : m_block_index) {
+        CBlockIndex* pindex = &entry.second;
         if (pindex->nFile == fileNumber) {
             pindex->nStatus &= ~BLOCK_HAVE_DATA;
             pindex->nStatus &= ~BLOCK_HAVE_UNDO;
@@ -202,12 +211,13 @@ CBlockIndex* BlockManager::InsertBlockIndex(const uint256& hash)
     // Return existing
     BlockMap::iterator mi = m_block_index.find(hash);
     if (mi != m_block_index.end()) {
-        return (*mi).second;
+        return &(*mi).second;
     }
 
     // Create new
-    CBlockIndex* pindexNew = new CBlockIndex();
-    mi = m_block_index.insert(std::make_pair(hash, pindexNew)).first;
+    CBlockIndex new_index{};
+    mi = m_block_index.insert(std::make_pair(hash, std::move(new_index))).first;
+    CBlockIndex* pindexNew = &(*mi).second;
     pindexNew->phashBlock = &((*mi).first);
 
     return pindexNew;
@@ -224,8 +234,8 @@ bool BlockManager::LoadBlockIndex(
     // Calculate nChainWork
     std::vector<std::pair<int, CBlockIndex*>> vSortedByHeight;
     vSortedByHeight.reserve(m_block_index.size());
-    for (const std::pair<const uint256, CBlockIndex*>& item : m_block_index) {
-        CBlockIndex* pindex = item.second;
+    for (std::pair<const uint256, CBlockIndex>& item : m_block_index) {
+        CBlockIndex* pindex = &item.second;
         vSortedByHeight.push_back(std::make_pair(pindex->nHeight, pindex));
     }
     sort(vSortedByHeight.begin(), vSortedByHeight.end());
@@ -327,10 +337,6 @@ void BlockManager::Unload()
 {
     m_blocks_unlinked.clear();
 
-    for (const BlockMap::value_type& entry : m_block_index) {
-        delete entry.second;
-    }
-
     m_block_index.clear();
 
     m_blockfile_info.clear();
@@ -386,8 +392,8 @@ bool BlockManager::LoadBlockIndexDB(ChainstateManager& chainman)
     // Check presence of blk files
     LogPrintf("Checking all blk files are present...\n");
     std::set<int> setBlkDataFiles;
-    for (const std::pair<const uint256, CBlockIndex*>& item : m_block_index) {
-        CBlockIndex* pindex = item.second;
+    for (const std::pair<const uint256, CBlockIndex>& item : m_block_index) {
+        const CBlockIndex* pindex = &item.second;
         if (pindex->nStatus & BLOCK_HAVE_DATA) {
             setBlkDataFiles.insert(pindex->nFile);
         }
diff --git a/src/node/blockstorage.h b/src/node/blockstorage.h
index 42e46797d2..be1ed83064 100644
--- a/src/node/blockstorage.h
+++ b/src/node/blockstorage.h
@@ -5,6 +5,7 @@
 #ifndef BITCOIN_NODE_BLOCKSTORAGE_H
 #define BITCOIN_NODE_BLOCKSTORAGE_H
 
+#include <chain.h>
 #include <fs.h>
 #include <protocol.h> // For CMessageHeader::MessageStartChars
 #include <sync.h>
@@ -20,7 +21,6 @@ class ArgsManager;
 class BlockValidationState;
 class CBlock;
 class CBlockFileInfo;
-class CBlockIndex;
 class CBlockUndo;
 class CChain;
 class CChainParams;
@@ -52,7 +52,11 @@ extern bool fPruneMode;
 /** Number of MiB of block files that we're trying to stay below. */
 extern uint64_t nPruneTarget;
 
-typedef std::unordered_map<uint256, CBlockIndex*, BlockHasher> BlockMap;
+// Because validation code takes pointers to the map's CBlockIndex objects, if
+// we ever switch to another associative container, we need to either use a
+// container that has stable addressing (true of all std associative
+// containers), or make the key a `std::unique_ptr<CBlockIndex>`
+typedef std::unordered_map<uint256, CBlockIndex, BlockHasher> BlockMap;
 
 struct CBlockIndexWorkComparator {
     bool operator()(const CBlockIndex* pa, const CBlockIndex* pb) const;
@@ -144,7 +148,8 @@ public:
     //! Mark one block file as pruned (modify associated database entries)
     void PruneOneBlockFile(const int fileNumber) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
-    CBlockIndex* LookupBlockIndex(const uint256& hash) const EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    CBlockIndex* LookupBlockIndex(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    const CBlockIndex* LookupBlockIndex(const uint256& hash) const EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     /** Get block file info entry for one block file */
     CBlockFileInfo* GetBlockFileInfo(size_t n);
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 9817c80cbd..2c69fdd457 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1753,10 +1753,10 @@ static RPCHelpMan getchaintips()
     std::set<const CBlockIndex*> setOrphans;
     std::set<const CBlockIndex*> setPrevs;
 
-    for (const std::pair<const uint256, CBlockIndex*>& item : chainman.BlockIndex()) {
-        if (!active_chain.Contains(item.second)) {
-            setOrphans.insert(item.second);
-            setPrevs.insert(item.second->pprev);
+    for (const std::pair<const uint256, CBlockIndex>& item : chainman.BlockIndex()) {
+        if (!active_chain.Contains(&item.second)) {
+            setOrphans.insert(&item.second);
+            setPrevs.insert(item.second.pprev);
         }
     }
 
diff --git a/src/validation.cpp b/src/validation.cpp
index 035b5783c3..fdb1518b3c 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1978,7 +1978,7 @@ bool CChainState::ConnectBlock(const CBlock& block, BlockValidationState& state,
         //  effectively caching the result of part of the verification.
         BlockMap::const_iterator  it = m_blockman.m_block_index.find(hashAssumeValid);
         if (it != m_blockman.m_block_index.end()) {
-            if (it->second->GetAncestor(pindex->nHeight) == pindex &&
+            if (it->second.GetAncestor(pindex->nHeight) == pindex &&
                 pindexBestHeader->GetAncestor(pindex->nHeight) == pindex &&
                 pindexBestHeader->nChainWork >= nMinimumChainWork) {
                 // This block is a member of the assumed verified chain and an ancestor of the best header.
@@ -3035,8 +3035,8 @@ bool CChainState::InvalidateBlock(BlockValidationState& state, CBlockIndex* pind
 
     {
         LOCK(cs_main);
-        for (const auto& entry : m_blockman.m_block_index) {
-            CBlockIndex *candidate = entry.second;
+        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.
@@ -3135,8 +3135,8 @@ bool CChainState::InvalidateBlock(BlockValidationState& state, CBlockIndex* pind
         // to setBlockIndexCandidates.
         BlockMap::iterator it = m_blockman.m_block_index.begin();
         while (it != m_blockman.m_block_index.end()) {
-            if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && !setBlockIndexCandidates.value_comp()(it->second, m_chain.Tip())) {
-                setBlockIndexCandidates.insert(it->second);
+            if (it->second.IsValid(BLOCK_VALID_TRANSACTIONS) && it->second.HaveTxsDownloaded() && !setBlockIndexCandidates.value_comp()(&it->second, m_chain.Tip())) {
+                setBlockIndexCandidates.insert(&it->second);
             }
             it++;
         }
@@ -3159,17 +3159,17 @@ void CChainState::ResetBlockFailureFlags(CBlockIndex *pindex) {
     // Remove the invalidity flag from this block and all its descendants.
     BlockMap::iterator it = m_blockman.m_block_index.begin();
     while (it != m_blockman.m_block_index.end()) {
-        if (!it->second->IsValid() && it->second->GetAncestor(nHeight) == pindex) {
-            it->second->nStatus &= ~BLOCK_FAILED_MASK;
-            m_blockman.m_dirty_blockindex.insert(it->second);
-            if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && setBlockIndexCandidates.value_comp()(m_chain.Tip(), it->second)) {
-                setBlockIndexCandidates.insert(it->second);
+        if (!it->second.IsValid() && it->second.GetAncestor(nHeight) == pindex) {
+            it->second.nStatus &= ~BLOCK_FAILED_MASK;
+            m_blockman.m_dirty_blockindex.insert(&it->second);
+            if (it->second.IsValid(BLOCK_VALID_TRANSACTIONS) && it->second.HaveTxsDownloaded() && setBlockIndexCandidates.value_comp()(m_chain.Tip(), &it->second)) {
+                setBlockIndexCandidates.insert(&it->second);
             }
-            if (it->second == m_chainman.m_best_invalid) {
+            if (&it->second == m_chainman.m_best_invalid) {
                 // Reset invalid block marker if it was pointing to one of those.
                 m_chainman.m_best_invalid = nullptr;
             }
-            m_chainman.m_failed_blocks.erase(it->second);
+            m_chainman.m_failed_blocks.erase(&it->second);
         }
         it++;
     }
@@ -3500,7 +3500,7 @@ bool ChainstateManager::AcceptBlockHeader(const CBlockHeader& block, BlockValida
     if (hash != chainparams.GetConsensus().hashGenesisBlock) {
         if (miSelf != m_blockman.m_block_index.end()) {
             // Block header is already known.
-            CBlockIndex* pindex = miSelf->second;
+            CBlockIndex* pindex = &(miSelf->second);
             if (ppindex)
                 *ppindex = pindex;
             if (pindex->nStatus & BLOCK_FAILED_MASK) {
@@ -3522,7 +3522,7 @@ bool ChainstateManager::AcceptBlockHeader(const CBlockHeader& block, BlockValida
             LogPrint(BCLog::VALIDATION, "%s: %s prev block not found\n", __func__, hash.ToString());
             return state.Invalid(BlockValidationResult::BLOCK_MISSING_PREV, "prev-blk-not-found");
         }
-        pindexPrev = (*mi).second;
+        pindexPrev = &((*mi).second);
         if (pindexPrev->nStatus & BLOCK_FAILED_MASK) {
             LogPrint(BCLog::VALIDATION, "%s: %s prev block invalid\n", __func__, hash.ToString());
             return state.Invalid(BlockValidationResult::BLOCK_INVALID_PREV, "bad-prevblk");
@@ -3988,13 +3988,13 @@ bool CChainState::ReplayBlocks()
     if (m_blockman.m_block_index.count(hashHeads[0]) == 0) {
         return error("ReplayBlocks(): reorganization to unknown block requested");
     }
-    pindexNew = m_blockman.m_block_index[hashHeads[0]];
+    pindexNew = &(m_blockman.m_block_index[hashHeads[0]]);
 
     if (!hashHeads[1].IsNull()) { // The old tip is allowed to be 0, indicating it's the first flush.
         if (m_blockman.m_block_index.count(hashHeads[1]) == 0) {
             return error("ReplayBlocks(): reorganization from unknown block requested");
         }
-        pindexOld = m_blockman.m_block_index[hashHeads[1]];
+        pindexOld = &(m_blockman.m_block_index[hashHeads[1]]);
         pindexFork = LastCommonAncestor(pindexOld, pindexNew);
         assert(pindexFork != nullptr);
     }
@@ -4261,8 +4261,8 @@ void CChainState::CheckBlockIndex()
 
     // Build forward-pointing map of the entire block tree.
     std::multimap<CBlockIndex*,CBlockIndex*> forward;
-    for (const std::pair<const uint256, CBlockIndex*>& entry : m_blockman.m_block_index) {
-        forward.insert(std::make_pair(entry.second->pprev, entry.second));
+    for (std::pair<const uint256, CBlockIndex>& entry : m_blockman.m_block_index) {
+        forward.insert(std::make_pair(entry.second.pprev, &entry.second));
     }
 
     assert(forward.size() == m_blockman.m_block_index.size());
diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 7693c9c0e8..c59f7e6f05 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -367,10 +367,10 @@ static int64_t AddTx(ChainstateManager& chainman, CWallet& wallet, uint32_t lock
     CBlockIndex* block = nullptr;
     if (blockTime > 0) {
         LOCK(cs_main);
-        auto inserted = chainman.BlockIndex().emplace(GetRandHash(), new CBlockIndex);
+        auto inserted = chainman.BlockIndex().emplace(std::piecewise_construct, std::make_tuple(GetRandHash()), std::make_tuple());
         assert(inserted.second);
         const uint256& hash = inserted.first->first;
-        block = inserted.first->second;
+        block = &inserted.first->second;
         block->nTime = blockTime;
         block->phashBlock = &hash;
         state = TxStateConfirmed{hash, block->nHeight, /*position_in_block=*/0};