Backport #10231: [Qt] Reduce a significant cs_main lock freeze

src/qt/bitcoingui.cpp

@@ -615,6 +615,7 @@ void BitcoinGUI::setClientModel(ClientModel *clientModel)
         connect(clientModel, SIGNAL(numConnectionsChanged(int)), this, SLOT(setNumConnections(int)));
         connect(clientModel, SIGNAL(networkActiveChanged(bool)), this, SLOT(setNetworkActive(bool)));
 
+        modalOverlay->setKnownBestHeight(clientModel->getHeaderTipHeight(), QDateTime::fromTime_t(clientModel->getHeaderTipTime()));
         setNumBlocks(clientModel->getNumBlocks(), clientModel->getLastBlockDate(), clientModel->getVerificationProgress(NULL), false);
         connect(clientModel, SIGNAL(numBlocksChanged(int,QDateTime,double,bool)), this, SLOT(setNumBlocks(int,QDateTime,double,bool)));
 
@@ -644,8 +645,6 @@ void BitcoinGUI::setClientModel(ClientModel *clientModel)
             // initialize the disable state of the tray icon with the current value in the model.
             setTrayIconVisible(optionsModel->getHideTrayIcon());
         }
-
-        modalOverlay->setKnownBestHeight(clientModel->getHeaderTipHeight(), QDateTime::fromTime_t(clientModel->getHeaderTipTime()));
     } else {
         // Disable possibility to show main window via action
         toggleHideAction->setEnabled(false);

src/qt/clientmodel.cpp

@@ -42,6 +42,8 @@ ClientModel::ClientModel(OptionsModel *optionsModel, QObject *parent) :
     banTableModel(0),
     pollTimer(0)
 {
+    cachedBestHeaderHeight = -1;
+    cachedBestHeaderTime = -1;
     peerTableModel = new PeerTableModel(this);
     banTableModel = new BanTableModel(this);
     pollTimer = new QTimer(this);
@@ -97,18 +99,28 @@ int ClientModel::getNumBlocks() const
 
 int ClientModel::getHeaderTipHeight() const
 {
-    LOCK(cs_main);
-    if (!pindexBestHeader)
-        return 0;
-    return pindexBestHeader->nHeight;
+    if (cachedBestHeaderHeight == -1) {
+        // make sure we initially populate the cache via a cs_main lock
+        // otherwise we need to wait for a tip update
+        LOCK(cs_main);
+        if (pindexBestHeader) {
+            cachedBestHeaderHeight = pindexBestHeader->nHeight;
+            cachedBestHeaderTime = pindexBestHeader->GetBlockTime();
+        }
+    }
+    return cachedBestHeaderHeight;
 }
 
 int64_t ClientModel::getHeaderTipTime() const
 {
-    LOCK(cs_main);
-    if (!pindexBestHeader)
-        return 0;
-    return pindexBestHeader->GetBlockTime();
+    if (cachedBestHeaderTime == -1) {
+        LOCK(cs_main);
+        if (pindexBestHeader) {
+            cachedBestHeaderHeight = pindexBestHeader->nHeight;
+            cachedBestHeaderTime = pindexBestHeader->GetBlockTime();
+        }
+    }
+    return cachedBestHeaderTime;
 }
 
 quint64 ClientModel::getTotalBytesRecv() const
@@ -337,6 +349,11 @@ static void BlockTipChanged(ClientModel *clientmodel, bool initialSync, const CB
 
     int64_t& nLastUpdateNotification = fHeader ? nLastHeaderTipUpdateNotification : nLastBlockTipUpdateNotification;
 
+    if (fHeader) {
+        // cache best headers time and height to reduce future cs_main locks
+        clientmodel->cachedBestHeaderHeight = pIndex->nHeight;
+        clientmodel->cachedBestHeaderTime = pIndex->GetBlockTime();
+    }
     // if we are in-sync, update the UI regardless of last update time
     if (!initialSync || now - nLastUpdateNotification > MODEL_UPDATE_DELAY) {
         //pass a async signal to the UI thread

src/qt/clientmodel.h

@@ -9,6 +9,8 @@
 #include <QObject>
 #include <QDateTime>
 
+#include <atomic>
+
 class AddressTableModel;
 class BanTableModel;
 class OptionsModel;
@@ -84,6 +86,10 @@ class ClientModel : public QObject
     QString formatClientStartupTime() const;
     QString dataDir() const;
 
+    // caches for the best header
+    mutable std::atomic<int> cachedBestHeaderHeight;
+    mutable std::atomic<int64_t> cachedBestHeaderTime;
+
 private:
     OptionsModel *optionsModel;
     PeerTableModel *peerTableModel;