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

4082fb0 Add missing <atomic> header in clientmodel.h (Jonas Schnelli)
928d4a9 Set both time/height header caches at the same time (Jonas Schnelli)
610a917 Declare headers height/time cache mutable, re-set the methods const (Jonas Schnelli)
cf92bce Update the remaining blocks left in modaloverlay at init. (Jonas Schnelli)
7148f5e Reduce cs_main locks during modal overlay by adding an atomic cache (Jonas Schnelli)

Tree-SHA512: a92ca22f90b8b2a5e8eb94fdce531ef44542e21a8dbbb0693f7723d7018592cb68de687a2a0aac91d31cbf019793f8e922550656d2b130ed3d854d60630341db

3 files changed, 32 insertions, 10 deletions

diff --git a/src/qt/bitcoingui.cpp b/src/qt/bitcoingui.cpp
index be79a67990..5c26baef9e 100644
--- a/src/qt/bitcoingui.cpp
+++ b/src/qt/bitcoingui.cpp
@@ -478,6 +478,7 @@ 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)));
 
@@ -505,8 +506,6 @@ 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);
diff --git a/src/qt/clientmodel.cpp b/src/qt/clientmodel.cpp
index bb10e49422..20d4687971 100644
--- a/src/qt/clientmodel.cpp
+++ b/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);
@@ -74,18 +76,28 @@ 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
@@ -283,6 +295,11 @@ 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
diff --git a/src/qt/clientmodel.h b/src/qt/clientmodel.h
index 2c10e633b8..4c92e2144e 100644
--- a/src/qt/clientmodel.h
+++ b/src/qt/clientmodel.h
@@ -8,6 +8,8 @@
 #include <QObject>
 #include <QDateTime>
 
+#include <atomic>
+
 class AddressTableModel;
 class BanTableModel;
 class OptionsModel;
@@ -81,6 +83,10 @@ public:
     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;