[Qt] catch Windows shutdown events while client is running

- prevents unsafe shutdowns on Windows, which is known to be
  able to cause problems with wallet.dat
- if a users ends a Windows session, this will initiate a client shutdown
  and show a Windows dialog, that tells the user what is going on (for
  Windows Vista and higher it will even show a reason for blocking the
  Windows session end)

src/qt/Makefile.am

@@ -211,7 +211,8 @@ BITCOIN_QT_H = \
   walletframe.h \
   walletmodel.h \
   walletmodeltransaction.h \
-  walletview.h
+  walletview.h \
+  winshutdownmonitor.h
 
 RES_ICONS = \
   res/icons/add.png \
@@ -277,7 +278,8 @@ BITCOIN_QT_CPP = \
   rpcconsole.cpp \
   splashscreen.cpp \
   trafficgraphwidget.cpp \
-  utilitydialog.cpp
+  utilitydialog.cpp \
+  winshutdownmonitor.cpp
 
 if ENABLE_WALLET
 BITCOIN_QT_CPP += \

src/qt/bitcoin.cpp

@@ -15,6 +15,7 @@
 #include "optionsmodel.h"
 #include "splashscreen.h"
 #include "utilitydialog.h"
+#include "winshutdownmonitor.h"
 #ifdef ENABLE_WALLET
 #include "paymentserver.h"
 #include "walletmodel.h"
@@ -189,6 +190,9 @@ class BitcoinApplication: public QApplication
     /// Get process return value
     int getReturnValue() { return returnValue; }
 
+    /// Get window identifier of QMainWindow (BitcoinGUI)
+    WId getMainWinId() const;
+
 public slots:
     void initializeResult(int retval);
     void shutdownResult(int retval);
@@ -444,6 +448,14 @@ void BitcoinApplication::handleRunawayException(const QString &message)
     ::exit(1);
 }
 
+WId BitcoinApplication::getMainWinId() const
+{
+    if (!window)
+        return 0;
+
+    return window->winId();
+}
+
 #ifndef BITCOIN_QT_TEST
 int main(int argc, char *argv[])
 {
@@ -558,10 +570,15 @@ int main(int argc, char *argv[])
     /// 9. Main GUI initialization
     // Install global event filter that makes sure that long tooltips can be word-wrapped
     app.installEventFilter(new GUIUtil::ToolTipToRichTextFilter(TOOLTIP_WRAP_THRESHOLD, &app));
-    // Install qDebug() message handler to route to debug.log
 #if QT_VERSION < 0x050000
+    // Install qDebug() message handler to route to debug.log
     qInstallMsgHandler(DebugMessageHandler);
 #else
+#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());
+#endif
+    // Install qDebug() message handler to route to debug.log
     qInstallMessageHandler(DebugMessageHandler);
 #endif
     // Load GUI settings from QSettings
@@ -577,6 +594,9 @@ int main(int argc, char *argv[])
     {
         app.createWindow(isaTestNet);
         app.requestInitialize();
+#if defined(Q_OS_WIN) && QT_VERSION >= 0x050000
+        WinShutdownMonitor::registerShutdownBlockReason(QObject::tr("Bitcoin Core did't yet exit safely..."), (HWND)app.getMainWinId());
+#endif
         app.exec();
         app.requestShutdown();
         app.exec();

src/qt/winshutdownmonitor.cpp

@@ -0,0 +1,57 @@
+// Copyright (c) 2014 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "winshutdownmonitor.h"
+
+#if defined(Q_OS_WIN) && QT_VERSION >= 0x050000
+#include "init.h"
+
+#include <windows.h>
+
+#include <QDebug>
+
+// If we don't want a message to be processed by Qt, return true and set result to
+// the value that the window procedure should return. Otherwise return false.
+bool WinShutdownMonitor::nativeEventFilter(const QByteArray &eventType, void *pMessage, long *pnResult)
+{
+       Q_UNUSED(eventType);
+
+       MSG *pMsg = static_cast<MSG *>(pMessage);
+
+       switch(pMsg->message)
+       {
+           case WM_QUERYENDSESSION:
+           {
+               // Initiate a client shutdown after receiving a WM_QUERYENDSESSION and block
+               // Windows session end until we have finished client shutdown.
+               StartShutdown();
+               *pnResult = FALSE;
+               return true;
+           }
+
+           case WM_ENDSESSION:
+           {
+               *pnResult = FALSE;
+               return true;
+           }
+       }
+
+       return false;
+}
+
+void WinShutdownMonitor::registerShutdownBlockReason(const QString& strReason, const HWND& mainWinId)
+{
+    typedef BOOL (WINAPI *PSHUTDOWNBRCREATE)(HWND, LPCWSTR);
+    PSHUTDOWNBRCREATE shutdownBRCreate = (PSHUTDOWNBRCREATE)GetProcAddress(GetModuleHandleA("User32.dll"), "ShutdownBlockReasonCreate");
+    if (shutdownBRCreate == NULL) {
+        qDebug() << "registerShutdownBlockReason : GetProcAddress for ShutdownBlockReasonCreate failed";
+        return;
+    }
+
+    if (shutdownBRCreate(mainWinId, strReason.toStdWString().c_str()))
+        qDebug() << "registerShutdownBlockReason : Successfully registered: " + strReason;
+    else
+        qDebug() << "registerShutdownBlockReason : Failed to register: " + strReason;
+}
+#endif

src/qt/winshutdownmonitor.h

@@ -0,0 +1,29 @@
+// Copyright (c) 2014 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef WINSHUTDOWNMONITOR_H
+#define WINSHUTDOWNMONITOR_H
+
+#ifdef WIN32
+#include <QByteArray>
+#include <QString>
+
+#if QT_VERSION >= 0x050000
+#include <windef.h> // for HWND
+
+#include <QAbstractNativeEventFilter>
+
+class WinShutdownMonitor : public QAbstractNativeEventFilter
+{
+public:
+    /** Implements QAbstractNativeEventFilter interface for processing Windows messages */
+    bool nativeEventFilter(const QByteArray &eventType, void *pMessage, long *pnResult);
+
+    /** Register the reason for blocking shutdown on Windows to allow clean client exit */
+    static void registerShutdownBlockReason(const QString& strReason, const HWND& mainWinId);
+};
+#endif
+#endif
+
+#endif // WINSHUTDOWNMONITOR_H