Merge bitcoin#15280: gui: Fix shutdown order

0dd6a8c Check m_internals in UnregisterValidationInterface (João Barbosa)
fd6d499 gui: Fix m_node.startShutdown() order (João Barbosa)
07b9aad gui: Expose BitcoinGUI::unsubscribeFromCoreSignals (João Barbosa)
60e190c gui: Fix WalletController deletion (João Barbosa)

Pull request description:

  This PR consists in small fixes in order to have a clean shutdown from the GUI.

Tree-SHA512: a9c641f202bc810698c4a39d5c5a1f54e54bdab098c412d65418879e00764a9db9f38383813914d591e24e097e49f177942b2ae6c57bba05dcc095e8a1d0b8f4

src/qt/bitcoin.cpp

@@ -218,6 +218,8 @@ BitcoinApplication::~BitcoinApplication()
 #ifdef ENABLE_WALLET
     delete paymentServer;
     paymentServer = nullptr;
+    delete m_wallet_controller;
+    m_wallet_controller = nullptr;
 #endif
     delete optionsModel;
     optionsModel = nullptr;
@@ -307,18 +309,20 @@ void BitcoinApplication::requestShutdown()
     qDebug() << __func__ << ": Requesting shutdown";
     startThread();
     window->hide();
+    // Must disconnect node signals otherwise current thread can deadlock since
+    // no event loop is running.
+    window->unsubscribeFromCoreSignals();
+    // Request node shutdown, which can interrupt long operations, like
+    // rescanning a wallet.
+    m_node.startShutdown();
+    // Unsetting the client model can cause the current thread to wait for node
+    // to complete an operation, like wait for a RPC execution to complate.
     window->setClientModel(nullptr);
     pollShutdownTimer->stop();
 
-#ifdef ENABLE_WALLET
-    delete m_wallet_controller;
-    m_wallet_controller = nullptr;
-#endif
     delete clientModel;
     clientModel = nullptr;
 
-    m_node.startShutdown();
-
     // Request shutdown from core thread
     Q_EMIT requestedShutdown();
 }

src/qt/bitcoingui.h

@@ -95,6 +95,9 @@ class BitcoinGUI : public QMainWindow
     */
     bool hasTrayIcon() const { return trayIcon; }
 
+    /** Disconnect core signals from GUI client */
+    void unsubscribeFromCoreSignals();
+
 protected:
     void changeEvent(QEvent *e);
     void closeEvent(QCloseEvent *event);
@@ -184,8 +187,6 @@ class BitcoinGUI : public QMainWindow
 
     /** Connect core signals to GUI client */
     void subscribeToCoreSignals();
-    /** Disconnect core signals from GUI client */
-    void unsubscribeFromCoreSignals();
 
     /** Update UI with latest network info from model. */
     void updateNetworkState();

src/validationinterface.cpp

@@ -107,7 +107,9 @@ void RegisterValidationInterface(CValidationInterface* pwalletIn) {
 }
 
 void UnregisterValidationInterface(CValidationInterface* pwalletIn) {
-    g_signals.m_internals->m_connMainSignals.erase(pwalletIn);
+    if (g_signals.m_internals) {
+        g_signals.m_internals->m_connMainSignals.erase(pwalletIn);
+    }
 }
 
 void UnregisterAllValidationInterfaces() {