Fix csBestBlock/cvBlockChange waiting in rpc/mining

Github-Pull: #12743
Rebased-From: 45dd13503918e75a45ce33eb5c934b998790fdc8

src/rpc/mining.cpp

@@ -477,7 +477,7 @@ UniValue getblocktemplate(const JSONRPCRequest& request)
             checktxtime = std::chrono::steady_clock::now() + std::chrono::minutes(1);
 
             WaitableLock lock(csBestBlock);
-            while (chainActive.Tip()->GetBlockHash() == hashWatchedChain && IsRPCRunning())
+            while (hashBestBlock == hashWatchedChain && IsRPCRunning())
             {
                 if (cvBlockChange.wait_until(lock, checktxtime) == std::cv_status::timeout)
                 {

src/validation.cpp

@@ -210,6 +210,7 @@ CChain& chainActive = g_chainstate.chainActive;
 CBlockIndex *pindexBestHeader = nullptr;
 CWaitableCriticalSection csBestBlock;
 CConditionVariable cvBlockChange;
+uint256 hashBestBlock;
 int nScriptCheckThreads = 0;
 std::atomic_bool fImporting(false);
 std::atomic_bool fReindex(false);
@@ -2151,7 +2152,11 @@ void static UpdateTip(const CBlockIndex *pindexNew, const CChainParams& chainPar
     // New best block
     mempool.AddTransactionsUpdated(1);
 
+    {
+        WaitableLock lock(csBestBlock);
+        hashBestBlock = pindexNew->GetBlockHash();
         cvBlockChange.notify_all();
+    }
 
     std::vector<std::string> warningMessages;
     if (!IsInitialBlockDownload())

src/validation.h

@@ -166,6 +166,7 @@ extern uint64_t nLastBlockWeight;
 extern const std::string strMessageMagic;
 extern CWaitableCriticalSection csBestBlock;
 extern CConditionVariable cvBlockChange;
+extern uint256 hashBestBlock;
 extern std::atomic_bool fImporting;
 extern std::atomic_bool fReindex;
 extern int nScriptCheckThreads;