Implement clean shutdown after receiving Unix signals, resolves #169

The database wasn't saved properly and lockfiles were not removed when receiving the signals SIGINT, SIGTERM, SIGQUIT or SIGHUP. This patch implements signal handling and performs a clean shutdown after receiving SIGINT SIGTERM or SIGQUIT and ignores SIGHUP.

Since this uses POSIX syscalls for signal and socket handling, there is no Windows implementation at the moment.

src/gui/Application.cpp

@@ -17,12 +17,21 @@
  */
 
 #include "Application.h"
+#include "MainWindow.h"
 
 #include <QAbstractNativeEventFilter>
 #include <QFileOpenEvent>
+#include <QSocketNotifier>
 
 #include "autotype/AutoType.h"
 
+#if defined(Q_OS_UNIX)
+#include <signal.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#endif
+
+class MainWindow;
 #if defined(Q_OS_UNIX) && !defined(Q_OS_OSX)
 class XcbEventFilter : public QAbstractNativeEventFilter
 {
@@ -64,13 +73,16 @@ public:
 
 Application::Application(int& argc, char** argv)
     : QApplication(argc, argv)
-    , m_mainWindow(nullptr)
+    , m_mainWindow(nullptr), m_unixSignalNotifier(nullptr)
 {
 #if defined(Q_OS_UNIX) && !defined(Q_OS_OSX)
     installNativeEventFilter(new XcbEventFilter());
 #elif defined(Q_OS_WIN)
     installNativeEventFilter(new WinEventFilter());
 #endif
+#if defined(Q_OS_UNIX)
+    registerUnixSignals();
+#endif
 }
 
 void Application::setMainWindow(QWidget* mainWindow)
@@ -98,3 +110,56 @@ bool Application::event(QEvent* event)
 
     return QApplication::event(event);
 }
+
+#if defined(Q_OS_UNIX)
+int Application::unixSignalSocket[2];
+
+void Application::registerUnixSignals()
+{
+    int result = ::socketpair(AF_UNIX, SOCK_STREAM, 0, unixSignalSocket);
+    Q_ASSERT(0 == result);
+    if (0 != result) {
+        // do not register handles when socket creation failed, otherwise
+        // application will be unresponsive to signals such as SIGINT or SIGTERM
+        return;
+    }
+    
+    QVector<int> const handledSignals = { SIGQUIT, SIGINT, SIGTERM, SIGHUP };
+    for (auto s: handledSignals) {
+        struct sigaction sigAction;
+        
+        sigAction.sa_handler = handleUnixSignal;
+        sigemptyset(&sigAction.sa_mask);
+        sigAction.sa_flags = 0 | SA_RESTART;
+        sigaction(s, &sigAction, nullptr);
+    }
+    
+    m_unixSignalNotifier = new QSocketNotifier(unixSignalSocket[1], QSocketNotifier::Read, this);
+    connect(m_unixSignalNotifier, SIGNAL(activated(int)), this, SLOT(quitBySignal()));
+}
+
+void Application::handleUnixSignal(int sig)
+{
+    switch (sig) {
+        case SIGQUIT:
+        case SIGINT:
+        case SIGTERM:
+        {
+            char buf = 0;
+            ::write(unixSignalSocket[0], &buf, sizeof(buf));
+            return;
+        }
+        case SIGHUP:
+            return;
+    }
+}
+
+void Application::quitBySignal()
+{
+    char buf;
+    ::read(unixSignalSocket[1], &buf, sizeof(buf));
+    
+    if (nullptr != m_mainWindow)
+        static_cast<MainWindow*>(m_mainWindow)->appExit();
+}
+#endif

src/gui/Application.h

@@ -21,6 +21,8 @@
 
 #include <QApplication>
 
+class QSocketNotifier;
+
 class Application : public QApplication
 {
     Q_OBJECT
@@ -34,8 +36,21 @@ public:
 Q_SIGNALS:
     void openFile(const QString& filename);
 
-private:
+private Q_SLOTS:
+    void quitBySignal();
+
+private:    
     QWidget* m_mainWindow;
+    
+#if defined(Q_OS_UNIX)
+    /**
+     * Register Unix signals such as SIGINT and SIGTERM for clean shutdown.
+     */
+    void registerUnixSignals();
+    QSocketNotifier* m_unixSignalNotifier;
+    static void handleUnixSignal(int sig);
+    static int unixSignalSocket[2];
+#endif
 };
 
 #endif // KEEPASSX_APPLICATION_H

src/gui/MainWindow.h

@@ -42,6 +42,7 @@ public:
 public Q_SLOTS:
     void openDatabase(const QString& fileName, const QString& pw = QString(),
                       const QString& keyFile = QString());
+    void appExit();
 
 protected:
      void closeEvent(QCloseEvent* event) override;
@@ -68,7 +69,6 @@ private Q_SLOTS:
     void applySettingsChanges();
     void trayIconTriggered(QSystemTrayIcon::ActivationReason reason);
     void toggleWindow();
-    void appExit();
     void lockDatabasesAfterInactivity();
     void repairDatabase();