Merge #12743: Fix csBestBlock/cvBlockChange waiting in rpc/mining

4a6c0e3dcf Modernize best block mutex/cv/hash variable naming (Pieter Wuille)
45dd135039 Fix csBestBlock/cvBlockChange waiting in rpc/mining (Pieter Wuille)

Pull request description:

  This is an alternative to #11694.

  It reintroduces a uint256 variable with the best block hash, protected by csBestBlock, and only updated while holding it.

  Also rename the involved variable to modern guidelines, as there are very few uses.

Tree-SHA512: 826a86c7d3cee7fe49f99f4398ae99e81cb0563197eaeba77306a3ca6072b67cdb932bc35720fc0f99c2a57b218efa029d0b8bdfb240591a629b2e90efa3199d

4 files changed, 15 insertions, 9 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 9edd93000..486c84f5a 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -323,7 +323,7 @@ void OnRPCStopped()
 {
     uiInterface.NotifyBlockTip.disconnect(&RPCNotifyBlockChange);
     RPCNotifyBlockChange(false, nullptr);
-    cvBlockChange.notify_all();
+    g_best_block_cv.notify_all();
     LogPrint(BCLog::RPC, "RPC stopped.\n");
 }
 
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 75bc98320..9a7c4b8e6 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -471,10 +471,10 @@ UniValue getblocktemplate(const JSONRPCRequest& request)
         {
             checktxtime = std::chrono::steady_clock::now() + std::chrono::minutes(1);
 
-            WaitableLock lock(csBestBlock);
-            while (chainActive.Tip()->GetBlockHash() == hashWatchedChain && IsRPCRunning())
+            WaitableLock lock(g_best_block_mutex);
+            while (g_best_block == hashWatchedChain && IsRPCRunning())
             {
-                if (cvBlockChange.wait_until(lock, checktxtime) == std::cv_status::timeout)
+                if (g_best_block_cv.wait_until(lock, checktxtime) == std::cv_status::timeout)
                 {
                     // Timeout: Check transactions for update
                     if (mempool.GetTransactionsUpdated() != nTransactionsUpdatedLastLP)
diff --git a/src/validation.cpp b/src/validation.cpp
index 8066e6c7a..cbbc857fd 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);
@@ -2204,7 +2205,11 @@ 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())
diff --git a/src/validation.h b/src/validation.h
index dad6858b1..366848469 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -165,8 +165,9 @@ extern BlockMap& mapBlockIndex;
 extern uint64_t nLastBlockTx;
 extern uint64_t nLastBlockWeight;
 extern const std::string strMessageMagic;
-extern CWaitableCriticalSection csBestBlock;
-extern CConditionVariable cvBlockChange;
+extern CWaitableCriticalSection g_best_block_mutex;
+extern CConditionVariable g_best_block_cv;
+extern uint256 g_best_block;
 extern std::atomic_bool fImporting;
 extern std::atomic_bool fReindex;
 extern int nScriptCheckThreads;