Merge #17737: Add ChainstateManager, remove BlockManager global

c9017ce3bc protect g_chainman with cs_main (James O'Beirne)
2b081c4568 test: add basic tests for ChainstateManager (James O'Beirne)
4ae29f5f0c use ChainstateManager to initialize chainstate (James O'Beirne)
5b690f0aae refactor: move RewindBlockIndex to CChainState (James O'Beirne)
89cdf4d569 validation: introduce unused ChainstateManager (James O'Beirne)
8e2ecfe249 validation: add CChainState.m_from_snapshot_blockhash (James O'Beirne)

Pull request description:

  This is part of the [assumeutxo project](https://github.com/bitcoin/bitcoin/projects/11):

  Parent PR: #15606
  Issue: #15605
  Specification: https://github.com/jamesob/assumeutxo-docs/tree/master/proposal

  ---

  This changeset introduces `ChainstateManager`, which is responsible for creating and managing access to multiple chainstates. Until we allow chainstate creation from UTXO snapshots (next assumeutxo PR?) it's basically unnecessary, but it is a prerequisite for background IBD support.

  Changes are also made to the initialization process to make use of `g_chainman` and thus clear the way for multiple chainstates being loaded on startup.

  One immediate benefit of this change is that we no longer have the `g_blockman` global, but instead have the ChainstateManager inject a reference of its shared BlockManager into any chainstate it creates.

  Another immediate benefit is that uses of `ChainActive()` and `ChainstateActive()` are now covered by lock annotations. Because use of `g_chainman` is annotated to require cs_main, these two functions subsequently follow.

  Because of whitespace changes, this diff looks bigger than it is. E.g., 4813167d98 is most easily reviewed with
  ```sh
  git show --color-moved=dimmed_zebra -w 4813167d98
  ```

ACKs for top commit:
  MarcoFalke:
    re-ACK c9017ce3bc 📙
  fjahr:
    Code Review Re-ACK c9017ce3bc
  ariard:
    Code Review ACK c9017ce
  ryanofsky:
    Code review ACK c9017ce3bc. No changes since last review other than a straight rebase

Tree-SHA512: 3f250d0dc95d4bfd70852ef1e39e081a4a9b71a4453f276e6d474c2ae06ad6ae6a32b4173084fe499e1e9af72dd9007f4a8a375c63ce9ac472ffeaada41ab508

src/validation.cpp

@@ -20,6 +20,7 @@
 #include <index/txindex.h>
 #include <logging.h>
 #include <logging/timer.h>
+#include <optional.h>
 #include <policy/fees.h>
 #include <policy/policy.h>
 #include <policy/settings.h>
@@ -76,20 +77,19 @@ bool CBlockIndexWorkComparator::operator()(const CBlockIndex *pa, const CBlockIn
     return false;
 }
 
-namespace {
-BlockManager g_blockman;
-} // anon namespace
+ChainstateManager g_chainman;
 
-std::unique_ptr<CChainState> g_chainstate;
-
-CChainState& ChainstateActive() {
-    assert(g_chainstate);
-    return *g_chainstate;
+CChainState& ChainstateActive()
+{
+    LOCK(::cs_main);
+    assert(g_chainman.m_active_chainstate);
+    return *g_chainman.m_active_chainstate;
 }
 
-CChain& ChainActive() {
-    assert(g_chainstate);
-    return g_chainstate->m_chain;
+CChain& ChainActive()
+{
+    LOCK(::cs_main);
+    return ::ChainstateActive().m_chain;
 }
 
 /**
@@ -151,8 +151,8 @@ namespace {
 CBlockIndex* LookupBlockIndex(const uint256& hash)
 {
     AssertLockHeld(cs_main);
-    BlockMap::const_iterator it = g_blockman.m_block_index.find(hash);
-    return it == g_blockman.m_block_index.end() ? nullptr : it->second;
+    BlockMap::const_iterator it = g_chainman.BlockIndex().find(hash);
+    return it == g_chainman.BlockIndex().end() ? nullptr : it->second;
 }
 
 CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& locator)
@@ -1242,10 +1242,9 @@ void CoinsViews::InitCache()
     m_cacheview = MakeUnique<CCoinsViewCache>(&m_catcherview);
 }
 
-// NOTE: for now m_blockman is set to a global, but this will be changed
-// in a future commit.
-CChainState::CChainState() : m_blockman(g_blockman) {}
-
+CChainState::CChainState(BlockManager& blockman, uint256 from_snapshot_blockhash)
+    : m_blockman(blockman),
+      m_from_snapshot_blockhash(from_snapshot_blockhash) {}
 
 void CChainState::InitCoinsDB(
     size_t cache_size_bytes,
@@ -1253,6 +1252,10 @@ void CChainState::InitCoinsDB(
     bool should_wipe,
     std::string leveldb_name)
 {
+    if (!m_from_snapshot_blockhash.IsNull()) {
+        leveldb_name += "_" + m_from_snapshot_blockhash.ToString();
+    }
+
     m_coins_views = MakeUnique<CoinsViews>(
         leveldb_name, cache_size_bytes, in_memory, should_wipe);
 }
@@ -1294,7 +1297,8 @@ static CBlockIndex *pindexBestForkTip = nullptr, *pindexBestForkBase = nullptr;
 
 BlockMap& BlockIndex()
 {
-    return g_blockman.m_block_index;
+    LOCK(::cs_main);
+    return g_chainman.m_blockman.m_block_index;
 }
 
 static void AlertNotify(const std::string& strMessage)
@@ -3443,7 +3447,7 @@ static bool ContextualCheckBlockHeader(const CBlockHeader& block, BlockValidatio
     if (fCheckpointsEnabled) {
         // Don't accept any forks from the main chain prior to last checkpoint.
         // GetLastCheckpoint finds the last checkpoint in MapCheckpoints that's in our
-        // g_blockman.m_block_index.
+        // BlockIndex().
         CBlockIndex* pcheckpoint = GetLastCheckpoint(params.Checkpoints());
         if (pcheckpoint && nHeight < pcheckpoint->nHeight) {
             LogPrintf("ERROR: %s: forked chain older than last checkpoint (height %d)\n", __func__, nHeight);
@@ -3651,7 +3655,8 @@ bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, BlockValid
         LOCK(cs_main);
         for (const CBlockHeader& header : headers) {
             CBlockIndex *pindex = nullptr; // Use a temp pindex instead of ppindex to avoid a const_cast
-            bool accepted = g_blockman.AcceptBlockHeader(header, state, chainparams, &pindex);
+            bool accepted = g_chainman.m_blockman.AcceptBlockHeader(
+                header, state, chainparams, &pindex);
             ::ChainstateActive().CheckBlockIndex(chainparams.GetConsensus());
 
             if (!accepted) {
@@ -3853,7 +3858,7 @@ void PruneOneBlockFile(const int fileNumber)
 {
     LOCK(cs_LastBlockFile);
 
-    for (const auto& entry : g_blockman.m_block_index) {
+    for (const auto& entry : g_chainman.BlockIndex()) {
         CBlockIndex* pindex = entry.second;
         if (pindex->nFile == fileNumber) {
             pindex->nStatus &= ~BLOCK_HAVE_DATA;
@@ -3867,12 +3872,12 @@ void PruneOneBlockFile(const int fileNumber)
             // to be downloaded again in order to consider its chain, at which
             // point it would be considered as a candidate for
             // m_blocks_unlinked or setBlockIndexCandidates.
-            auto range = g_blockman.m_blocks_unlinked.equal_range(pindex->pprev);
+            auto range = g_chainman.m_blockman.m_blocks_unlinked.equal_range(pindex->pprev);
             while (range.first != range.second) {
                 std::multimap<CBlockIndex *, CBlockIndex *>::iterator _it = range.first;
                 range.first++;
                 if (_it->second == pindex) {
-                    g_blockman.m_blocks_unlinked.erase(_it);
+                    g_chainman.m_blockman.m_blocks_unlinked.erase(_it);
                 }
             }
         }
@@ -4109,9 +4114,11 @@ void BlockManager::Unload() {
 
 bool static LoadBlockIndexDB(const CChainParams& chainparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
-    if (!g_blockman.LoadBlockIndex(
-            chainparams.GetConsensus(), *pblocktree, ::ChainstateActive().setBlockIndexCandidates))
+    if (!g_chainman.m_blockman.LoadBlockIndex(
+            chainparams.GetConsensus(), *pblocktree,
+            ::ChainstateActive().setBlockIndexCandidates)) {
         return false;
+    }
 
     // Load block file info
     pblocktree->ReadLastBlockFile(nLastBlockFile);
@@ -4133,7 +4140,7 @@ bool static LoadBlockIndexDB(const CChainParams& chainparams) EXCLUSIVE_LOCKS_RE
     // 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 : g_blockman.m_block_index)
+    for (const std::pair<const uint256, CBlockIndex*>& item : g_chainman.BlockIndex())
     {
         CBlockIndex* pindex = item.second;
         if (pindex->nStatus & BLOCK_HAVE_DATA) {
@@ -4510,26 +4517,15 @@ bool CChainState::RewindBlockIndex(const CChainParams& params)
             PruneBlockIndexCandidates();
 
             CheckBlockIndex(params.GetConsensus());
-        }
-    }
 
-    return true;
-}
-
-bool RewindBlockIndex(const CChainParams& params) {
-    if (!::ChainstateActive().RewindBlockIndex(params)) {
-        return false;
-    }
-
-    LOCK(cs_main);
-    if (::ChainActive().Tip() != nullptr) {
-        // FlushStateToDisk can possibly read ::ChainActive(). Be conservative
-        // and skip it here, we're about to -reindex-chainstate anyway, so
-        // it'll get called a bunch real soon.
-        BlockValidationState state;
-        if (!::ChainstateActive().FlushStateToDisk(params, state, FlushStateMode::ALWAYS)) {
-            LogPrintf("RewindBlockIndex: unable to flush state to disk (%s)\n", state.ToString());
-            return false;
+            // FlushStateToDisk can possibly read ::ChainActive(). Be conservative
+            // and skip it here, we're about to -reindex-chainstate anyway, so
+            // it'll get called a bunch real soon.
+            BlockValidationState state;
+            if (!FlushStateToDisk(params, state, FlushStateMode::ALWAYS)) {
+                LogPrintf("RewindBlockIndex: unable to flush state to disk (%s)\n", state.ToString());
+                return false;
+            }
         }
     }
 
@@ -4547,8 +4543,7 @@ void CChainState::UnloadBlockIndex() {
 void UnloadBlockIndex()
 {
     LOCK(cs_main);
-    ::ChainActive().SetTip(nullptr);
-    g_blockman.Unload();
+    g_chainman.Unload();
     pindexBestInvalid = nullptr;
     pindexBestHeader = nullptr;
     mempool.clear();
@@ -4561,8 +4556,6 @@ void UnloadBlockIndex()
         warningcache[b].clear();
     }
     fHavePruned = false;
-
-    ::ChainstateActive().UnloadBlockIndex();
 }
 
 bool LoadBlockIndex(const CChainParams& chainparams)
@@ -4572,7 +4565,7 @@ bool LoadBlockIndex(const CChainParams& chainparams)
     if (!fReindex) {
         bool ret = LoadBlockIndexDB(chainparams);
         if (!ret) return false;
-        needs_init = g_blockman.m_block_index.empty();
+        needs_init = g_chainman.m_blockman.m_block_index.empty();
     }
 
     if (needs_init) {
@@ -4693,7 +4686,7 @@ bool LoadExternalBlockFile(const CChainParams& chainparams, FILE* fileIn, FlatFi
                 // Activate the genesis block so normal node progress can continue
                 if (hash == chainparams.GetConsensus().hashGenesisBlock) {
                     BlockValidationState state;
-                    if (!ActivateBestChain(state, chainparams)) {
+                    if (!ActivateBestChain(state, chainparams, nullptr)) {
                         break;
                     }
                 }
@@ -4923,6 +4916,14 @@ void CChainState::CheckBlockIndex(const Consensus::Params& consensusParams)
     assert(nNodes == forward.size());
 }
 
+std::string CChainState::ToString()
+{
+    CBlockIndex* tip = m_chain.Tip();
+    return strprintf("Chainstate [%s] @ height %d (%s)",
+        m_from_snapshot_blockhash.IsNull() ? "ibd" : "snapshot",
+        tip ? tip->nHeight : -1, tip ? tip->GetBlockHash().ToString() : "null");
+}
+
 std::string CBlockFileInfo::ToString() const
 {
     return strprintf("CBlockFileInfo(blocks=%u, size=%u, heights=%u...%u, time=%s...%s)", nBlocks, nSize, nHeightFirst, nHeightLast, FormatISO8601Date(nTimeFirst), FormatISO8601Date(nTimeLast));
@@ -5110,10 +5111,99 @@ public:
     CMainCleanup() {}
     ~CMainCleanup() {
         // block headers
-        BlockMap::iterator it1 = g_blockman.m_block_index.begin();
-        for (; it1 != g_blockman.m_block_index.end(); it1++)
+        BlockMap::iterator it1 = g_chainman.BlockIndex().begin();
+        for (; it1 != g_chainman.BlockIndex().end(); it1++)
             delete (*it1).second;
-        g_blockman.m_block_index.clear();
+        g_chainman.BlockIndex().clear();
     }
 };
 static CMainCleanup instance_of_cmaincleanup;
+
+Optional<uint256> ChainstateManager::SnapshotBlockhash() const {
+    if (m_active_chainstate != nullptr) {
+        // If a snapshot chainstate exists, it will always be our active.
+        return m_active_chainstate->m_from_snapshot_blockhash;
+    }
+    return {};
+}
+
+std::vector<CChainState*> ChainstateManager::GetAll()
+{
+    std::vector<CChainState*> out;
+
+    if (!IsSnapshotValidated() && m_ibd_chainstate) {
+        out.push_back(m_ibd_chainstate.get());
+    }
+
+    if (m_snapshot_chainstate) {
+        out.push_back(m_snapshot_chainstate.get());
+    }
+
+    return out;
+}
+
+CChainState& ChainstateManager::InitializeChainstate(const uint256& snapshot_blockhash)
+{
+    bool is_snapshot = !snapshot_blockhash.IsNull();
+    std::unique_ptr<CChainState>& to_modify =
+        is_snapshot ? m_snapshot_chainstate : m_ibd_chainstate;
+
+    if (to_modify) {
+        throw std::logic_error("should not be overwriting a chainstate");
+    }
+
+    to_modify.reset(new CChainState(m_blockman, snapshot_blockhash));
+
+    // Snapshot chainstates and initial IBD chaintates always become active.
+    if (is_snapshot || (!is_snapshot && !m_active_chainstate)) {
+        LogPrintf("Switching active chainstate to %s\n", to_modify->ToString());
+        m_active_chainstate = to_modify.get();
+    } else {
+        throw std::logic_error("unexpected chainstate activation");
+    }
+
+    return *to_modify;
+}
+
+CChain& ChainstateManager::ActiveChain() const
+{
+    assert(m_active_chainstate);
+    return m_active_chainstate->m_chain;
+}
+
+bool ChainstateManager::IsSnapshotActive() const
+{
+    return m_snapshot_chainstate && m_active_chainstate == m_snapshot_chainstate.get();
+}
+
+CChainState& ChainstateManager::ValidatedChainstate() const
+{
+    if (m_snapshot_chainstate && IsSnapshotValidated()) {
+        return *m_snapshot_chainstate.get();
+    }
+    assert(m_ibd_chainstate);
+    return *m_ibd_chainstate.get();
+}
+
+bool ChainstateManager::IsBackgroundIBD(CChainState* chainstate) const
+{
+    return (m_snapshot_chainstate && chainstate == m_ibd_chainstate.get());
+}
+
+void ChainstateManager::Unload()
+{
+    for (CChainState* chainstate : this->GetAll()) {
+        chainstate->m_chain.SetTip(nullptr);
+        chainstate->UnloadBlockIndex();
+    }
+
+    m_blockman.Unload();
+}
+
+void ChainstateManager::Reset()
+{
+    m_ibd_chainstate.reset();
+    m_snapshot_chainstate.reset();
+    m_active_chainstate = nullptr;
+    m_snapshot_validated = false;
+}