Reduce cs_main locks during modal overlay by adding an atomic cache

Author: jonasschnelli

src/qt/clientmodel.cpp

@@ -36,6 +36,8 @@ 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);
@@ -72,20 +74,28 @@ int ClientModel::getNumBlocks() const
     return chainActive.Height();
 }
 
-int ClientModel::getHeaderTipHeight() const
+int ClientModel::getHeaderTipHeight()
 {
-    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;
+        }
+    }
+    return cachedBestHeaderHeight;
 }
 
-int64_t ClientModel::getHeaderTipTime() const
+int64_t ClientModel::getHeaderTipTime()
 {
-    LOCK(cs_main);
-    if (!pindexBestHeader)
-        return 0;
-    return pindexBestHeader->GetBlockTime();
+    if (cachedBestHeaderTime == -1) {
+        LOCK(cs_main);
+        if (pindexBestHeader) {
+            cachedBestHeaderTime = pindexBestHeader->GetBlockTime();
+        }
+    }
+    return cachedBestHeaderTime;
 }
 
 quint64 ClientModel::getTotalBytesRecv() const
@@ -283,6 +293,11 @@ 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

@@ -51,8 +51,8 @@ class ClientModel : public QObject
     //! Return number of connections, default is in- and outbound (total)
     int getNumConnections(unsigned int flags = CONNECTIONS_ALL) const;
     int getNumBlocks() const;
-    int getHeaderTipHeight() const;
-    int64_t getHeaderTipTime() const;
+    int getHeaderTipHeight();
+    int64_t getHeaderTipTime();
     //! Return number of transactions in the mempool
     long getMempoolSize() const;
     //! Return the dynamic memory usage of the mempool
@@ -81,6 +81,10 @@ class ClientModel : public QObject
     QString formatClientStartupTime() const;
     QString dataDir() const;
 
+    // caches for the best header
+    std::atomic<int> cachedBestHeaderHeight;
+    std::atomic<int64_t> cachedBestHeaderTime;
+
 private:
     OptionsModel *optionsModel;
     PeerTableModel *peerTableModel;