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.

1 files changed, 8 insertions, 3 deletions

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);