refactor: Remove call to StartShutdown from qt

Use interfaces::Node object instead.

There is a minor change in behavior in this commit, because the new code calls
InterruptRPC() and StopRPC() when previous code did not do this.  But this
should be a good thing since it makes sense to interrupt RPC when the system is
shutting down, and it is better for the GUI shut down in a consistent way
regardless of how the shutdown is triggered.

src/qt/bitcoin.cpp

@@ -661,7 +661,10 @@ int GuiMain(int argc, char* argv[])
     app.installEventFilter(new GUIUtil::LabelOutOfFocusEventFilter(&app));
 #if defined(Q_OS_WIN)
     // Install global event filter for processing Windows session related Windows messages (WM_QUERYENDSESSION and WM_ENDSESSION)
-    qApp->installNativeEventFilter(new WinShutdownMonitor());
+    // Note: it is safe to call app.node() in the lambda below despite the fact
+    // that app.createNode() hasn't been called yet, because native events will
+    // not be processed until the Qt event loop is executed.
+    qApp->installNativeEventFilter(new WinShutdownMonitor([&app] { app.node().startShutdown(); }));
 #endif
     // Install qDebug() message handler to route to debug.log
     qInstallMessageHandler(DebugMessageHandler);

src/qt/bitcoingui.h

@@ -315,7 +315,7 @@ public Q_SLOTS:
     /** Simply calls showNormalIfMinimized(true) */
     void toggleHidden();
 
-    /** called by a timer to check if ShutdownRequested() has been set **/
+    /** called by a timer to check if shutdown has been requested */
     void detectShutdown();
 
     /** Show progress dialog e.g. for verifychain */

src/qt/test/apptests.cpp

@@ -11,7 +11,6 @@
 #include <qt/bitcoingui.h>
 #include <qt/networkstyle.h>
 #include <qt/rpcconsole.h>
-#include <shutdown.h>
 #include <test/util/setup_common.h>
 #include <validation.h>
 

src/qt/winshutdownmonitor.cpp

@@ -5,7 +5,6 @@
 #include <qt/winshutdownmonitor.h>
 
 #if defined(Q_OS_WIN)
-#include <shutdown.h>
 
 #include <windows.h>
 
@@ -25,7 +24,7 @@ bool WinShutdownMonitor::nativeEventFilter(const QByteArray &eventType, void *pM
            {
                // Initiate a client shutdown after receiving a WM_QUERYENDSESSION and block
                // Windows session end until we have finished client shutdown.
-               StartShutdown();
+               m_shutdown_fn();
                *pnResult = FALSE;
                return true;
            }

src/qt/winshutdownmonitor.h

@@ -8,6 +8,7 @@
 #ifdef WIN32
 #include <QByteArray>
 #include <QString>
+#include <functional>
 
 #include <windef.h> // for HWND
 
@@ -16,11 +17,16 @@
 class WinShutdownMonitor : public QAbstractNativeEventFilter
 {
 public:
+    WinShutdownMonitor(std::function<void()> shutdown_fn) : m_shutdown_fn{std::move(shutdown_fn)} {}
+
     /** Implements QAbstractNativeEventFilter interface for processing Windows messages */
     bool nativeEventFilter(const QByteArray &eventType, void *pMessage, long *pnResult) override;
 
     /** Register the reason for blocking shutdown on Windows to allow clean client exit */
     static void registerShutdownBlockReason(const QString& strReason, const HWND& mainWinId);
+
+private:
+    std::function<void()> m_shutdown_fn;
 };
 #endif