wallet refactor: Avoid use of Chain::Lock in CWallet::RescanFromTime

This is a step toward removing the Chain::Lock class and reducing cs_main
locking.

This change has no effect on behavior.

Author: ryanofsky

src/interfaces/chain.cpp

@@ -260,6 +260,11 @@ class ChainImpl : public Chain
         WAIT_LOCK(cs_main, lock);
         return FillBlock(LookupBlockIndex(hash), block, lock);
     }
+    bool findFirstBlockWithTimeAndHeight(int64_t min_time, int min_height, const FoundBlock& block) override
+    {
+        WAIT_LOCK(cs_main, lock);
+        return FillBlock(ChainActive().FindEarliestAtLeast(min_time, min_height), block, lock);
+    }
     bool findAncestorByHeight(const uint256& block_hash, int ancestor_height, const FoundBlock& ancestor_out) override
     {
         WAIT_LOCK(cs_main, lock);

src/interfaces/chain.h

@@ -146,6 +146,12 @@ class Chain
     //! or contents.
     virtual bool findBlock(const uint256& hash, const FoundBlock& block={}) = 0;
 
+    //! Find first block in the chain with timestamp >= the given time
+    //! and height >= than the given height, return false if there is no block
+    //! with a high enough timestamp and height. Optionally return block
+    //! information.
+    virtual bool findFirstBlockWithTimeAndHeight(int64_t min_time, int min_height, const FoundBlock& block={}) = 0;
+
     //! Find ancestor of block at specified height and optionally return
     //! ancestor information.
     virtual bool findAncestorByHeight(const uint256& block_hash, int ancestor_height, const FoundBlock& ancestor_out={}) = 0;

src/test/interfaces_tests.cpp

@@ -47,6 +47,18 @@ BOOST_AUTO_TEST_CASE(findBlock)
     BOOST_CHECK(!chain->findBlock({}, FoundBlock()));
 }
 
+BOOST_AUTO_TEST_CASE(findFirstBlockWithTimeAndHeight)
+{
+    auto chain = interfaces::MakeChain(m_node);
+    auto& active = ChainActive();
+    uint256 hash;
+    int height;
+    BOOST_CHECK(chain->findFirstBlockWithTimeAndHeight(/* min_time= */ 0, /* min_height= */ 5, FoundBlock().hash(hash).height(height)));
+    BOOST_CHECK_EQUAL(hash, active[5]->GetBlockHash());
+    BOOST_CHECK_EQUAL(height, 5);
+    BOOST_CHECK(!chain->findFirstBlockWithTimeAndHeight(/* min_time= */ active.Tip()->GetBlockTimeMax() + 1, /* min_height= */ 0));
+}
+
 BOOST_AUTO_TEST_CASE(findAncestorByHeight)
 {
     auto chain = interfaces::MakeChain(m_node);

src/wallet/wallet.cpp

@@ -1591,15 +1591,12 @@ int64_t CWallet::RescanFromTime(int64_t startTime, const WalletRescanReserver& r
     // Find starting block. May be null if nCreateTime is greater than the
     // highest blockchain timestamp, in which case there is nothing that needs
     // to be scanned.
+    int start_height = 0;
     uint256 start_block;
-    {
-        auto locked_chain = chain().lock();
-        const Optional<int> start_height = locked_chain->findFirstBlockWithTimeAndHeight(startTime - TIMESTAMP_WINDOW, 0, &start_block);
-        const Optional<int> tip_height = locked_chain->getHeight();
-        WalletLogPrintf("%s: Rescanning last %i blocks\n", __func__, tip_height && start_height ? *tip_height - *start_height + 1 : 0);
-    }
+    bool start = chain().findFirstBlockWithTimeAndHeight(startTime - TIMESTAMP_WINDOW, 0, FoundBlock().hash(start_block).height(start_height));
+    WalletLogPrintf("%s: Rescanning last %i blocks\n", __func__, start ? WITH_LOCK(cs_wallet, return GetLastBlockHeight()) - start_height + 1 : 0);
 
-    if (!start_block.IsNull()) {
+    if (start) {
         // TODO: this should take into account failure by ScanResult::USER_ABORT
         ScanResult result = ScanForWalletTransactions(start_block, {} /* stop_block */, reserver, update);
         if (result.status == ScanResult::FAILURE) {