qt: Prevent thread/memory leak on exiting RPCConsole

Make ownership of the QThread object clear, so that the RPCConsole
can wait for the executor thread to quit before shutdown is called. This
increases overall thread safety, and prevents some objects from leaking
on exit.

Author: laanwj

src/qt/bitcoin.cpp

@@ -409,6 +409,11 @@ void BitcoinApplication::requestInitialize()
 
 void BitcoinApplication::requestShutdown()
 {
+    // Show a simple window indicating shutdown status
+    // Do this first as some of the steps may take some time below,
+    // for example the RPC console may still be executing a command.
+    ShutdownWindow::showShutdownWindow(window);
+
     qDebug() << __func__ << ": Requesting shutdown";
     startThread();
     window->hide();
@@ -423,9 +428,6 @@ void BitcoinApplication::requestShutdown()
     delete clientModel;
     clientModel = 0;
 
-    // Show a simple window indicating shutdown status
-    ShutdownWindow::showShutdownWindow(window);
-
     // Request shutdown from core thread
     Q_EMIT requestedShutdown();
 }

src/qt/bitcoingui.cpp

@@ -511,6 +511,13 @@ void BitcoinGUI::setClientModel(ClientModel *_clientModel)
             // Disable context menu on tray icon
             trayIconMenu->clear();
         }
+        // Propagate cleared model to child objects
+        rpcConsole->setClientModel(nullptr);
+#ifdef ENABLE_WALLET
+        walletFrame->setClientModel(nullptr);
+#endif // ENABLE_WALLET
+        unitDisplayControl->setOptionsModel(nullptr);
+        connectionsControl->setClientModel(nullptr);
     }
 }
 
@@ -1242,7 +1249,5 @@ void NetworkToggleStatusBarControl::mousePressEvent(QMouseEvent *event)
 /** Lets the control know about the Client Model */
 void NetworkToggleStatusBarControl::setClientModel(ClientModel *_clientModel)
 {
-    if (_clientModel) {
-        this->clientModel = _clientModel;
-    }
+    this->clientModel = _clientModel;
 }

src/qt/rpcconsole.cpp

@@ -382,7 +382,6 @@ RPCConsole::RPCConsole(const PlatformStyle *_platformStyle, QWidget *parent) :
     // based timer interface
     RPCSetTimerInterfaceIfUnset(rpcTimerInterface);
 
-    startExecutor();
     setTrafficGraphRange(INITIAL_TRAFFIC_GRAPH_MINS);
 
     ui->detailWidget->hide();
@@ -396,7 +395,6 @@ RPCConsole::RPCConsole(const PlatformStyle *_platformStyle, QWidget *parent) :
 RPCConsole::~RPCConsole()
 {
     GUIUtil::saveWindowGeometry("nRPCConsoleWindow", this);
-    Q_EMIT stopExecutor();
     RPCUnsetTimerInterface(rpcTimerInterface);
     delete rpcTimerInterface;
     delete ui;
@@ -565,6 +563,14 @@ void RPCConsole::setClientModel(ClientModel *model)
         autoCompleter = new QCompleter(wordList, this);
         ui->lineEdit->setCompleter(autoCompleter);
         autoCompleter->popup()->installEventFilter(this);
+        // Start thread to execute RPC commands.
+        startExecutor();
+    }
+    if (!model) {
+        // Client model is being set to 0, this means shutdown() is about to be called.
+        // Make sure we clean up the executor thread
+        Q_EMIT stopExecutor();
+        thread.wait();
     }
 }
 
@@ -759,26 +765,24 @@ void RPCConsole::browseHistory(int offset)
 
 void RPCConsole::startExecutor()
 {
-    QThread *thread = new QThread;
     RPCExecutor *executor = new RPCExecutor();
-    executor->moveToThread(thread);
+    executor->moveToThread(&thread);
 
     // Replies from executor object must go to this object
     connect(executor, SIGNAL(reply(int,QString)), this, SLOT(message(int,QString)));
     // Requests from this object must go to executor
     connect(this, SIGNAL(cmdRequest(QString)), executor, SLOT(request(QString)));
 
     // On stopExecutor signal
-    // - queue executor for deletion (in execution thread)
     // - quit the Qt event loop in the execution thread
-    connect(this, SIGNAL(stopExecutor()), executor, SLOT(deleteLater()));
-    connect(this, SIGNAL(stopExecutor()), thread, SLOT(quit()));
-    // Queue the thread for deletion (in this thread) when it is finished
-    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));
+    connect(this, SIGNAL(stopExecutor()), &thread, SLOT(quit()));
+    // - queue executor for deletion (in execution thread)
+    connect(&thread, SIGNAL(finished()), executor, SLOT(deleteLater()), Qt::DirectConnection);
+    connect(&thread, SIGNAL(finished()), this, SLOT(test()), Qt::DirectConnection);
 
     // Default implementation of QThread::run() simply spins up an event loop in the thread,
     // which is what we want.
-    thread->start();
+    thread.start();
 }
 
 void RPCConsole::on_tabWidget_currentChanged(int index)

src/qt/rpcconsole.h

@@ -12,6 +12,7 @@
 
 #include <QWidget>
 #include <QCompleter>
+#include <QThread>
 
 class ClientModel;
 class PlatformStyle;
@@ -148,6 +149,7 @@ public Q_SLOTS:
     QMenu *banTableContextMenu;
     int consoleFontSize;
     QCompleter *autoCompleter;
+    QThread thread;
 
     /** Update UI with latest network info from model. */
     void updateNetworkState();