validation: assumeutxo: swap m_mempool on snapshot activation

Otherwise we will not receive transactions during background sync until
restart.

Author: jamesob

src/test/validation_chainstatemanager_tests.cpp

@@ -38,8 +38,6 @@ BOOST_FIXTURE_TEST_SUITE(validation_chainstatemanager_tests, TestingSetup)
 BOOST_FIXTURE_TEST_CASE(chainstatemanager, TestChain100Setup)
 {
     ChainstateManager& manager = *m_node.chainman;
-    CTxMemPool& mempool = *m_node.mempool;
-
     std::vector<Chainstate*> chainstates;
 
     BOOST_CHECK(!manager.SnapshotBlockhash().has_value());
@@ -69,8 +67,7 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager, TestChain100Setup)
     // Create a snapshot-based chainstate.
     //
     const uint256 snapshot_blockhash = active_tip->GetBlockHash();
-    Chainstate& c2 = WITH_LOCK(::cs_main, return manager.ActivateExistingSnapshot(
-        &mempool, snapshot_blockhash));
+    Chainstate& c2 = WITH_LOCK(::cs_main, return manager.ActivateExistingSnapshot(snapshot_blockhash));
     chainstates.push_back(&c2);
     c2.InitCoinsDB(
         /*cache_size_bytes=*/1 << 23, /*in_memory=*/true, /*should_wipe=*/false);
@@ -113,7 +110,6 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager, TestChain100Setup)
 BOOST_FIXTURE_TEST_CASE(chainstatemanager_rebalance_caches, TestChain100Setup)
 {
     ChainstateManager& manager = *m_node.chainman;
-    CTxMemPool& mempool = *m_node.mempool;
 
     size_t max_cache = 10000;
     manager.m_total_coinsdb_cache = max_cache;
@@ -137,7 +133,7 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_rebalance_caches, TestChain100Setup)
     // Create a snapshot-based chainstate.
     //
     CBlockIndex* snapshot_base{WITH_LOCK(manager.GetMutex(), return manager.ActiveChain()[manager.ActiveChain().Height() / 2])};
-    Chainstate& c2 = WITH_LOCK(cs_main, return manager.ActivateExistingSnapshot(&mempool, *snapshot_base->phashBlock));
+    Chainstate& c2 = WITH_LOCK(cs_main, return manager.ActivateExistingSnapshot(*snapshot_base->phashBlock));
     chainstates.push_back(&c2);
     c2.InitCoinsDB(
         /*cache_size_bytes=*/1 << 23, /*in_memory=*/true, /*should_wipe=*/false);
@@ -423,7 +419,6 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, SnapshotTestSetup)
 BOOST_FIXTURE_TEST_CASE(chainstatemanager_loadblockindex, TestChain100Setup)
 {
     ChainstateManager& chainman = *Assert(m_node.chainman);
-    CTxMemPool& mempool = *m_node.mempool;
     Chainstate& cs1 = chainman.ActiveChainstate();
 
     int num_indexes{0};
@@ -493,7 +488,7 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_loadblockindex, TestChain100Setup)
 
     // Note: cs2's tip is not set when ActivateExistingSnapshot is called.
     Chainstate& cs2 = WITH_LOCK(::cs_main,
-        return chainman.ActivateExistingSnapshot(&mempool, *assumed_base->phashBlock));
+        return chainman.ActivateExistingSnapshot(*assumed_base->phashBlock));
 
     // Set tip of the fully validated chain to be the validated tip
     cs1.m_chain.SetTip(*validated_tip);

src/validation.cpp

@@ -5268,6 +5268,12 @@ bool ChainstateManager::ActivateSnapshot(
         const bool chaintip_loaded = m_snapshot_chainstate->LoadChainTip();
         assert(chaintip_loaded);
 
+        // Transfer possession of the mempool to the snapshot chianstate.
+        // Mempool is empty at this point because we're still in IBD.
+        Assert(m_active_chainstate->m_mempool->size() == 0);
+        Assert(!m_snapshot_chainstate->m_mempool);
+        m_snapshot_chainstate->m_mempool = m_active_chainstate->m_mempool;
+        m_active_chainstate->m_mempool = nullptr;
         m_active_chainstate = m_snapshot_chainstate.get();
         m_blockman.m_snapshot_height = this->GetSnapshotBaseHeight();
 
@@ -5747,16 +5753,22 @@ bool ChainstateManager::DetectSnapshotChainstate(CTxMemPool* mempool)
     LogPrintf("[snapshot] detected active snapshot chainstate (%s) - loading\n",
         fs::PathToString(*path));
 
-    this->ActivateExistingSnapshot(mempool, *base_blockhash);
+    this->ActivateExistingSnapshot(*base_blockhash);
     return true;
 }
 
-Chainstate& ChainstateManager::ActivateExistingSnapshot(CTxMemPool* mempool, uint256 base_blockhash)
+Chainstate& ChainstateManager::ActivateExistingSnapshot(uint256 base_blockhash)
 {
     assert(!m_snapshot_chainstate);
     m_snapshot_chainstate =
-        std::make_unique<Chainstate>(mempool, m_blockman, *this, base_blockhash);
+        std::make_unique<Chainstate>(nullptr, m_blockman, *this, base_blockhash);
     LogPrintf("[snapshot] switching active chainstate to %s\n", m_snapshot_chainstate->ToString());
+
+    // Mempool is empty at this point because we're still in IBD.
+    Assert(m_active_chainstate->m_mempool->size() == 0);
+    Assert(!m_snapshot_chainstate->m_mempool);
+    m_snapshot_chainstate->m_mempool = m_active_chainstate->m_mempool;
+    m_active_chainstate->m_mempool = nullptr;
     m_active_chainstate = m_snapshot_chainstate.get();
     return *m_snapshot_chainstate;
 }

src/validation.h

@@ -1213,8 +1213,7 @@ class ChainstateManager
 
     //! Switch the active chainstate to one based on a UTXO snapshot that was loaded
     //! previously.
-    Chainstate& ActivateExistingSnapshot(CTxMemPool* mempool, uint256 base_blockhash)
-        EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+    Chainstate& ActivateExistingSnapshot(uint256 base_blockhash) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     //! If we have validated a snapshot chain during this runtime, copy its
     //! chainstate directory over to the main `chainstate` location, completing