1 files changed, 19 insertions, 14 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 8066e6c7a..3726cb3b1 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -202,8 +202,9 @@ CCriticalSection cs_main;
 BlockMap& mapBlockIndex = g_chainstate.mapBlockIndex;
 CChain& chainActive = g_chainstate.chainActive;
 CBlockIndex *pindexBestHeader = nullptr;
-CWaitableCriticalSection csBestBlock;
-CConditionVariable cvBlockChange;
+CWaitableCriticalSection g_best_block_mutex;
+CConditionVariable g_best_block_cv;
+uint256 g_best_block;
 int nScriptCheckThreads = 0;
 std::atomic_bool fImporting(false);
 std::atomic_bool fReindex(false);
@@ -263,7 +264,8 @@ CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& loc
 {
     AssertLockHeld(cs_main);
 
-    // Find the first block the caller has in the main chain
+    // Find the latest block common to locator and chain - we expect that
+    // locator.vHave is sorted descending by height.
     for (const uint256& hash : locator.vHave) {
         CBlockIndex* pindex = LookupBlockIndex(hash);
         if (pindex) {
@@ -352,7 +354,7 @@ bool CheckSequenceLocks(const CTransaction &tx, int flags, LockPoints* lp, bool
 
     CBlockIndex* tip = chainActive.Tip();
     assert(tip != nullptr);
-    
+
     CBlockIndex index;
     index.pprev = tip;
     // CheckSequenceLocks() uses chainActive.Height()+1 to evaluate
@@ -2204,7 +2206,11 @@ void static UpdateTip(const CBlockIndex *pindexNew, const CChainParams& chainPar
     // New best block
     mempool.AddTransactionsUpdated(1);
 
-    cvBlockChange.notify_all();
+    {
+        WaitableLock lock(g_best_block_mutex);
+        g_best_block = pindexNew->GetBlockHash();
+        g_best_block_cv.notify_all();
+    }
 
     std::vector<std::string> warningMessages;
     if (!IsInitialBlockDownload())
@@ -2672,18 +2678,17 @@ bool CChainState::ActivateBestChain(CValidationState &state, const CChainParams&
                 assert(trace.pblock && trace.pindex);
                 GetMainSignals().BlockConnected(trace.pblock, trace.pindex, trace.conflictedTxs);
             }
-        }
-        // When we reach this point, we switched to a new tip (stored in pindexNewTip).
-
-        // Notifications/callbacks that can run without cs_main
 
-        // Notify external listeners about the new tip.
-        GetMainSignals().UpdatedBlockTip(pindexNewTip, pindexFork, fInitialDownload);
+            // 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
+            GetMainSignals().UpdatedBlockTip(pindexNewTip, pindexFork, fInitialDownload);
 
-        // Always notify the UI if a new block tip was connected
-        if (pindexFork != pindexNewTip) {
-            uiInterface.NotifyBlockTip(fInitialDownload, pindexNewTip);
+            // Always notify the UI if a new block tip was connected
+            if (pindexFork != pindexNewTip) {
+                uiInterface.NotifyBlockTip(fInitialDownload, pindexNewTip);
+            }
         }
+        // When we reach this point, we switched to a new tip (stored in pindexNewTip).
 
         if (nStopAtHeight && pindexNewTip && pindexNewTip->nHeight >= nStopAtHeight) StartShutdown();