Merge #12988: Hold cs_main while calling UpdatedBlockTip() signal

d86edd3 Hold cs_main while calling UpdatedBlockTip() and ui.NotifyBlockTip (Jesse Cohen)

Pull request description:

  Resolves #12978

Tree-SHA512: 2aed09434cd8dbf541ea75462070b73ee87ff31409bede210f6999ffee4a37e32202a289efd37609485d4cbdfe134fe4660a10bfb41e8a8acdba7cd0b61b8780

Author: laanwj

src/validation.cpp

@@ -354,7 +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
@@ -2678,18 +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.
+            // Enqueue while holding cs_main to ensure that UpdatedBlockTip is called in the order in which blocks are connected
+            GetMainSignals().UpdatedBlockTip(pindexNewTip, pindexFork, fInitialDownload);
 
-        // Notify external listeners about the new tip.
-        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();
 

src/validationinterface.cpp

@@ -139,6 +139,10 @@ void CMainSignals::MempoolEntryRemoved(CTransactionRef ptx, MemPoolRemovalReason
 }
 
 void CMainSignals::UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) {
+    // Dependencies exist that require UpdatedBlockTip events to be delivered in the order in which
+    // the chain actually updates. One way to ensure this is for the caller to invoke this signal
+    // in the same critical section where the chain is updated
+
     m_internals->m_schedulerClient.AddToProcessQueue([pindexNew, pindexFork, fInitialDownload, this] {
         m_internals->UpdatedBlockTip(pindexNew, pindexFork, fInitialDownload);
     });