chain: add CChain::IsTipRecent helper

Factor the chain tip work/recency check out of `ChainstateManager::IsInitialBlockDownload()` into a reusable `CChain::IsTipRecent()` helper, and annotate it as requiring `cs_main` since it's reading mutable state.

Also introduce a local `chainman_ref` in the kernel import-blocks wrapper to reduce repetition and keep follow-up diffs small.

`IsInitialBlockDownload` returns were also unified to make the followup move clean.

Co-authored-by: Patrick Strateman <patrick.strateman@gmail.com>
Co-authored-by: Martin Zumsande <mzumsande@gmail.com>

src/chain.h

@@ -420,6 +420,15 @@ public:
         return int(vChain.size()) - 1;
     }
 
+    /** Check whether this chain's tip exists, has enough work, and is recent. */
+    bool IsTipRecent(const arith_uint256& min_chain_work, std::chrono::seconds max_tip_age) const EXCLUSIVE_LOCKS_REQUIRED(::cs_main)
+    {
+        const auto tip{Tip()};
+        return tip &&
+               tip->nChainWork >= min_chain_work &&
+               tip->Time() >= Now<NodeSeconds>() - max_tip_age;
+    }
+
     /** Set/initialize a chain with a given tip. */
     void SetTip(CBlockIndex& block);
 

src/kernel/bitcoinkernel.cpp

@@ -1054,7 +1054,8 @@ int btck_chainstate_manager_import_blocks(btck_ChainstateManager* chainman, cons
                 import_files.emplace_back(std::string{block_file_paths_data[i], block_file_paths_lens[i]}.c_str());
             }
         }
-        node::ImportBlocks(*btck_ChainstateManager::get(chainman).m_chainman, import_files);
+        auto& chainman_ref{*btck_ChainstateManager::get(chainman).m_chainman};
+        node::ImportBlocks(chainman_ref, import_files);
     } catch (const std::exception& e) {
         LogError("Failed to import blocks: %s", e.what());
         return -1;

src/validation.cpp

@@ -1947,25 +1947,12 @@ void Chainstate::InitCoinsCache(size_t cache_size_bytes)
 bool ChainstateManager::IsInitialBlockDownload() const
 {
     // Optimization: pre-test latch before taking the lock.
-    if (!m_cached_is_ibd.load(std::memory_order_relaxed))
+    if (!m_cached_is_ibd.load(std::memory_order_relaxed)) return false;
-        return false;
 
     LOCK(cs_main);
-    if (!m_cached_is_ibd.load(std::memory_order_relaxed))
+    if (!m_cached_is_ibd.load(std::memory_order_relaxed)) return false;
-        return false;
+    if (m_blockman.LoadingBlocks()) return true;
-    if (m_blockman.LoadingBlocks()) {
+    if (!ActiveChain().IsTipRecent(MinimumChainWork(), m_options.max_tip_age)) return true;
-        return true;
-    }
-    CChain& chain{ActiveChain()};
-    if (chain.Tip() == nullptr) {
-        return true;
-    }
-    if (chain.Tip()->nChainWork < MinimumChainWork()) {
-        return true;
-    }
-    if (chain.Tip()->Time() < Now<NodeSeconds>() - m_options.max_tip_age) {
-        return true;
-    }
     LogInfo("Leaving InitialBlockDownload (latching to false)");
     m_cached_is_ibd.store(false, std::memory_order_relaxed);
     return false;