Handle SIGTERM and SIGKILL (#4091)

* Handle sigint and sigterm when KDSingleApplication is used to prevent stale lock files

* fixing windows build

* cleanup after more review

src/core/CMakeLists.txt

@@ -13,6 +13,15 @@ target_sources(flameshot PRIVATE
     qguiappcurrentscreen.cpp
 )
 
-IF (WIN32)
+if (USE_KDSINGLEAPPLICATION)
+if (NOT WIN32)
+target_sources(flameshot PRIVATE
+    signaldaemon.h
+    signaldaemon.cpp
+)
+endif ()
+endif ()
+
+if (WIN32)
     target_sources(flameshot PRIVATE globalshortcutfilter.h globalshortcutfilter.cpp)
-ENDIF ()
+endif ()

src/core/signaldaemon.cpp

@@ -0,0 +1,62 @@
+#include "signaldaemon.h"
+#include <QApplication>
+#include <QSocketNotifier>
+#include <csignal>
+#include <qdebug.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+int SignalDaemon::sigintFd[2];
+int SignalDaemon::sigtermFd[2];
+
+SignalDaemon::SignalDaemon(QObject* parent)
+  : QObject(parent)
+{
+    if (::socketpair(AF_UNIX, SOCK_STREAM, 0, sigintFd))
+        qFatal("Couldn't create INT socketpair");
+
+    if (::socketpair(AF_UNIX, SOCK_STREAM, 0, sigtermFd))
+        qFatal("Couldn't create TERM socketpair");
+    snInt = new QSocketNotifier(sigintFd[1], QSocketNotifier::Read, this);
+    connect(
+      snInt, SIGNAL(activated(QSocketDescriptor)), this, SLOT(handleSigInt()));
+    snTerm = new QSocketNotifier(sigtermFd[1], QSocketNotifier::Read, this);
+    connect(snTerm,
+            SIGNAL(activated(QSocketDescriptor)),
+            this,
+            SLOT(handleSigTerm()));
+}
+
+void SignalDaemon::intSignalHandler(int)
+{
+    char msg = 1;
+    ::write(sigintFd[0], &msg, sizeof(msg));
+}
+
+void SignalDaemon::termSignalHandler(int)
+{
+    char msg = 1;
+    ::write(sigtermFd[0], &msg, sizeof(msg));
+}
+
+void SignalDaemon::handleSigTerm()
+{
+    snTerm->setEnabled(false);
+    char tmp = 0;
+    ::read(sigtermFd[1], &tmp, sizeof(tmp));
+
+    QApplication::quit();
+    snTerm->setEnabled(true);
+}
+
+void SignalDaemon::handleSigInt()
+{
+    snInt->setEnabled(false);
+
+    char tmp = 0;
+    ::read(sigintFd[1], &tmp, sizeof(tmp));
+
+    QApplication::quit();
+
+    snInt->setEnabled(true);
+}

src/core/signaldaemon.h

@@ -0,0 +1,27 @@
+#include <QObject>
+#include <QSocketNotifier>
+
+class SignalDaemon : public QObject
+{
+    Q_OBJECT
+
+public:
+    SignalDaemon(QObject* parent = 0);
+    ~SignalDaemon() = default;
+
+    // Unix signal handlers.
+    static void intSignalHandler(int unused);
+    static void termSignalHandler(int unused);
+
+public slots:
+    // Qt signal handlers.
+    void handleSigInt();
+    void handleSigTerm();
+
+private:
+    static int sigintFd[2];
+    static int sigtermFd[2];
+
+    QSocketNotifier* snInt;
+    QSocketNotifier* snTerm;
+};

src/main.cpp

@@ -3,6 +3,10 @@
 
 #ifdef USE_KDSINGLEAPPLICATION
 #include "kdsingleapplication.h"
+#ifdef Q_OS_UNIX
+#include "core/signaldaemon.h"
+#include "csignal"
+#endif
 #endif
 
 #include "abstractlogger.h"
@@ -34,6 +38,31 @@
 // Required for saving button list QList<CaptureTool::Type>
 Q_DECLARE_METATYPE(QList<int>)
 
+#if defined(USE_KDSINGLEAPPLICATION) && defined(Q_OS_UNIX)
+static int setup_unix_signal_handlers()
+{
+    struct sigaction sint, term;
+
+    sint.sa_handler = SignalDaemon::intSignalHandler;
+    sigemptyset(&sint.sa_mask);
+    sint.sa_flags = 0;
+    sint.sa_flags |= SA_RESTART;
+
+    if (sigaction(SIGINT, &sint, 0))
+        return 1;
+
+    term.sa_handler = SignalDaemon::termSignalHandler;
+    sigemptyset(&term.sa_mask);
+    term.sa_flags = 0;
+    term.sa_flags |= SA_RESTART;
+
+    if (sigaction(SIGTERM, &term, 0))
+        return 2;
+
+    return 0;
+}
+#endif
+
 int requestCaptureAndWait(const CaptureRequest& req)
 {
     Flameshot* flameshot = Flameshot::instance();
@@ -149,11 +178,13 @@ int main(int argc, char* argv[])
         QApplication app(argc, argv);
 
 #ifdef USE_KDSINGLEAPPLICATION
-        KDSingleApplication kdsa(QStringLiteral("flameshot"));
+#ifdef Q_OS_UNIX
+        setup_unix_signal_handlers();
+        auto signalDaemon = SignalDaemon();
+#endif
+        auto kdsa = KDSingleApplication(QStringLiteral("flameshot"));
 
         if (!kdsa.isPrimaryInstance()) {
-            // AbstractLogger::warning()
-            //  << QStringLiteral("Closing second Flameshot instance!");
             return 0; // Quit
         }
 #endif