validation: MaybeRebalanceCaches when chain leaves IBD

Check to see if we need to rebalance caches across chainstates when
a chain leaves IBD.

Author: jamesob

src/validation.cpp

@@ -3192,6 +3192,7 @@ bool Chainstate::ActivateBestChain(BlockValidationState& state, std::shared_ptr<
 
     CBlockIndex *pindexMostWork = nullptr;
     CBlockIndex *pindexNewTip = nullptr;
+    bool exited_ibd{false};
     do {
         // Block until the validation queue drains. This should largely
         // never happen in normal operation, however may happen during
@@ -3205,6 +3206,7 @@ bool Chainstate::ActivateBestChain(BlockValidationState& state, std::shared_ptr<
             LOCK(cs_main);
             // Lock transaction pool for at least as long as it takes for connectTrace to be consumed
             LOCK(MempoolMutex());
+            const bool was_in_ibd = m_chainman.IsInitialBlockDownload();
             CBlockIndex* starting_tip = m_chain.Tip();
             bool blocks_connected = false;
             do {
@@ -3252,16 +3254,21 @@ bool Chainstate::ActivateBestChain(BlockValidationState& state, std::shared_ptr<
             if (!blocks_connected) return true;
 
             const CBlockIndex* pindexFork = m_chain.FindFork(starting_tip);
-            bool fInitialDownload = m_chainman.IsInitialBlockDownload();
+            bool still_in_ibd = m_chainman.IsInitialBlockDownload();
+
+            if (was_in_ibd && !still_in_ibd) {
+                // Active chainstate has exited IBD.
+                exited_ibd = true;
+            }
 
             // Notify external listeners about the new tip.
             // Enqueue while holding cs_main to ensure that UpdatedBlockTip is called in the order in which blocks are connected
             if (pindexFork != pindexNewTip) {
                 // Notify ValidationInterface subscribers
-                GetMainSignals().UpdatedBlockTip(pindexNewTip, pindexFork, fInitialDownload);
+                GetMainSignals().UpdatedBlockTip(pindexNewTip, pindexFork, still_in_ibd);
 
                 // Always notify the UI if a new block tip was connected
-                if (kernel::IsInterrupted(m_chainman.GetNotifications().blockTip(GetSynchronizationState(fInitialDownload), *pindexNewTip))) {
+                if (kernel::IsInterrupted(m_chainman.GetNotifications().blockTip(GetSynchronizationState(still_in_ibd), *pindexNewTip))) {
                     // Just breaking and returning success for now. This could
                     // be changed to bubble up the kernel::Interrupted value to
                     // the caller so the caller could distinguish between
@@ -3272,6 +3279,13 @@ bool Chainstate::ActivateBestChain(BlockValidationState& state, std::shared_ptr<
         }
         // When we reach this point, we switched to a new tip (stored in pindexNewTip).
 
+        if (exited_ibd) {
+            // If a background chainstate is in use, we may need to rebalance our
+            // allocation of caches once a chainstate exits initial block download.
+            LOCK(::cs_main);
+            m_chainman.MaybeRebalanceCaches();
+        }
+
         if (WITH_LOCK(::cs_main, return m_disabled)) {
             // Background chainstate has reached the snapshot base block, so exit.
             break;