Crash recovery for plasma-shell

We restart plasma-shell after crashes. When it crashes subsequently on startup,
and more than two times in a row, we give up in order to not endlessly loop.
Once the shell process stays alive for at least 15 seconds, we reset the crash
counter, so a later crash, at runtime rather than on startup will still be
recovered from.

This logic is very similar as to how kwin handles it.

DIGEST:

src/shell/CMakeLists.txt

@@ -15,6 +15,7 @@ find_package(Qt5Qml REQUIRED)
 find_package(Qt5Quick REQUIRED)
 find_package(Qt5Script REQUIRED)
 find_package(KCoreAddons REQUIRED)
+find_package(KCrash REQUIRED)
 find_package(Solid REQUIRED)
 find_package(KActivities REQUIRED)
 
@@ -64,6 +65,7 @@ target_link_libraries(plasma-shell
  KF5::KIOCore
  KF5::KWindowSystem
  KF5::KCoreAddons
+ KF5::KCrash
  Plasma
  PlasmaQuick
  Qt5::Script

src/shell/main.cpp

@@ -36,17 +36,25 @@ int main(int argc, char** argv)
     QApplication app(argc, argv);
     app.setApplicationVersion(version);
 
-    QCommandLineOption dbg = QCommandLineOption(QStringList() << QStringLiteral("d") << QStringLiteral("qmljsdebugger"),
-                                        QStringLiteral("Enable QML Javascript debugger"));
+    QCommandLineOption dbg = QCommandLineOption(QStringList() << QStringLiteral("d") <<
+                                                QStringLiteral("qmljsdebugger"),
+                                                QStringLiteral("Enable QML Javascript debugger"));
 
-    QCommandLineOption windowed = QCommandLineOption(QStringList() << QStringLiteral("w") << QStringLiteral("windowed"),
-                                        QStringLiteral("force a windowed view for desktop purposes"));
+    QCommandLineOption windowed = QCommandLineOption(QStringList() << QStringLiteral("w") <<
+                                                     QStringLiteral("windowed"),
+                                                     QStringLiteral("Force a windowed view for testing purposes"));
+
+    QCommandLineOption crashesOption(QStringLiteral("crashes"),
+                                     QStringLiteral("Recent number of crashes"),
+                                     QStringLiteral("n"));
 
     parser.addVersionOption();
     parser.addHelpOption();
     parser.setApplicationDescription(description);
     parser.addOption(dbg);
     parser.addOption(windowed);
+    parser.addOption(crashesOption);
+
     parser.process(app);
 
     //enable the QML debugger only if --qmljsdebugger (or -d) is passed as a command line arg
@@ -56,16 +64,9 @@ int main(int argc, char** argv)
     }
 
     Plasma::PluginLoader::setPluginLoader(new ShellPluginLoader);
-    // DesktopCorona *corona = new DesktopCorona();
-    // corona->loadLayout();
-    // if (corona->containments().isEmpty()) {
-    //     corona->loadDefaultLayout();
-    // }
-    // corona->processUpdateScripts();
-    // corona->checkScreens();
 
+    ShellManager::setCrashCount(parser.value(crashesOption).toInt());
     ShellManager::s_forceWindowed = parser.isSet(windowed);
-
     ShellManager::instance();
 
     return app.exec();

src/shell/shellmanager.cpp

@@ -26,18 +26,23 @@
 #include <QList>
 #include <QTimer>
 
+#include <qplatformdefs.h>
 #include <QQmlEngine>
 #include <QQmlComponent>
 
 #include <config-prefix.h>
 #include "shellcorona.h"
 
+#include <kcrash.h>
+
 static const QString s_shellsDir(
         QString(CMAKE_INSTALL_PREFIX) + "/" + DATA_INSTALL_DIR + "/" + "plasma/shells/");
 static const QString s_shellLoaderPath = QString("/contents/loader.qml");
 
 bool ShellManager::s_forceWindowed = false;
 
+int ShellManager::crashes = 0;
+
 //
 // ShellManager
 //
@@ -60,6 +65,10 @@ public:
 ShellManager::ShellManager()
     : d(new Private())
 {
+    // Using setCrashHandler, we end up in an infinite loop instead of quitting,
+    // use setEmergencySaveFunction instead to avoid this.
+    KCrash::setEmergencySaveFunction(ShellManager::crashHandler);
+    QTimer::singleShot(15 * 1000, this, SLOT(resetCrashCount()));
 
     connect(
         &d->shellUpdateDelay, &QTimer::timeout,
@@ -203,3 +212,39 @@ ShellManager * ShellManager::instance()
     return &manager;
 }
 
+void ShellManager::setCrashCount(int count)
+{
+    crashes = count;
+}
+
+void ShellManager::resetCrashCount()
+{
+    crashes = 0;
+}
+
+void ShellManager::crashHandler(int signal)
+{
+    /* plasma-shell restart logic as crash recovery
+     *
+     * We restart plasma-shell after crashes. When it crashes subsequently on startup,
+     * and more than two times in a row, we give up in order to not endlessly loop.
+     * Once the shell process stays alive for at least 15 seconds, we reset the crash
+     * counter, so a later crash, at runtime rather than on startup will still be
+     * recovered from.
+     *
+     * This logic is very similar as to how kwin handles it.
+     */
+    crashes++;
+    fprintf(stderr, "Application::crashHandler() called with signal %d; recent crashes: %d\n", signal, crashes);
+    char cmd[1024];
+    sprintf(cmd, "%s --crashes %d &",
+            QFile::encodeName(QCoreApplication::applicationFilePath()).constData(), crashes);
+
+    if (crashes < 3) {
+        sleep(1);
+        system(cmd);
+    } else {
+        fprintf(stderr, "Too many crashes in short order, not restarting automatically.\n");
+    }
+
+}

src/shell/shellmanager.h

@@ -34,6 +34,8 @@ public:
 
     static bool s_forceWindowed;
 
+    static void setCrashCount(int count);
+
 protected Q_SLOTS:
     void registerHandler(QObject * handler);
     void deregisterHandler(QObject * handler);
@@ -45,11 +47,17 @@ public Q_SLOTS:
 Q_SIGNALS:
     void shellChanged(const QString & shell);
 
+private Q_SLOTS:
+    void resetCrashCount();
+
 private:
     ShellManager();
 
     class Private;
     const QScopedPointer<Private> d;
+
+    static int crashes;
+    static void crashHandler(int signal);
 };
 
 #endif /* SHELLMANAGER_H */