[kwin-wayland] Create dedicated thread for wayland connection

The Wayland event queue is moved into a dedicated thread and a
new class is created for just creating the connection and listening
for events. The WaylandBackend creates the thread and uses an event
queue for the main thread.

REVIEW: 119761

CMakeLists.txt

@@ -397,7 +397,10 @@ if(KWIN_HAVE_EGL)
 endif()
 
 if(Wayland_Client_FOUND AND XKB_FOUND)
-    set(kwin_KDEINIT_SRCS ${kwin_KDEINIT_SRCS} wayland_backend.cpp)
+    set(kwin_KDEINIT_SRCS
+            ${kwin_KDEINIT_SRCS}
+            wayland_backend.cpp
+            wayland_client/connection_thread.cpp)
     if(KWIN_HAVE_EGL AND Wayland_Egl_FOUND)
         set(kwin_KDEINIT_SRCS ${kwin_KDEINIT_SRCS} egl_wayland_backend.cpp)
     endif()

autotests/CMakeLists.txt

@@ -1,4 +1,9 @@
 add_definitions(-DKWIN_UNIT_TEST)
+
+if(Wayland_Client_FOUND AND XKB_FOUND)
+    add_subdirectory(wayland_client)
+endif()
+
 ########################################################
 # Test ScreenPaintData
 ########################################################

autotests/wayland_client/CMakeLists.txt

@@ -0,0 +1,8 @@
+########################################################
+# Test WaylandConnectionThread
+########################################################
+set( testWaylandConnectionThread_SRCS test_wayland_connection_thread.cpp ${KWIN_SOURCE_DIR}/wayland_client/connection_thread.cpp )
+add_executable(testWaylandConnectionThread ${testWaylandConnectionThread_SRCS})
+target_link_libraries( testWaylandConnectionThread Qt5::Test Wayland::Client)
+add_test(kwin-testWaylandConnectionThread testWaylandConnectionThread)
+ecm_mark_as_test(testWaylandConnectionThread)

autotests/wayland_client/test_wayland_connection_thread.cpp

@@ -0,0 +1,222 @@
+/********************************************************************
+KWin - the KDE window manager
+This file is part of the KDE project.
+
+Copyright (C) 2014 Martin Gräßlin <mgraesslin@kde.org>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*********************************************************************/
+// Qt
+#include <QtTest/QtTest>
+// KWin
+#include "../../wayland_client/connection_thread.h"
+// Wayland
+#include <wayland-client-protocol.h>
+
+class TestWaylandConnectionThread : public QObject
+{
+    Q_OBJECT
+public:
+    explicit TestWaylandConnectionThread(QObject *parent = nullptr);
+private Q_SLOTS:
+    void init();
+    void cleanup();
+
+    void testInitConnectionNoThread();
+    void testConnectionFailure();
+    void testConnectionDieing();
+    void testConnectionThread();
+
+private:
+    QProcess *m_westonProcess;
+};
+
+static const QString s_socketName = QStringLiteral("kwin-test-wayland-connection-0");
+
+TestWaylandConnectionThread::TestWaylandConnectionThread(QObject *parent)
+    : QObject(parent)
+    , m_westonProcess(nullptr)
+{
+}
+
+void TestWaylandConnectionThread::init()
+{
+    QVERIFY(!m_westonProcess);
+    // starts weston
+    m_westonProcess = new QProcess(this);
+    m_westonProcess->setProgram(QStringLiteral("weston"));
+
+    m_westonProcess->setArguments(QStringList({QStringLiteral("--socket=%1").arg(s_socketName), QStringLiteral("--no-config")}));
+    m_westonProcess->start();
+    QVERIFY(m_westonProcess->waitForStarted());
+
+    // wait for the socket to appear
+    QDir runtimeDir(qgetenv("XDG_RUNTIME_DIR"));
+    if (runtimeDir.exists(s_socketName)) {
+        return;
+    }
+    QFileSystemWatcher *socketWatcher = new QFileSystemWatcher(QStringList({runtimeDir.absolutePath()}), this);
+    QSignalSpy socketSpy(socketWatcher, SIGNAL(directoryChanged(QString)));
+
+    // limit to maximum of 10 waits
+    for (int i = 0; i < 10; ++i) {
+        QVERIFY(socketSpy.wait());
+        if (runtimeDir.exists(s_socketName)) {
+            delete socketWatcher;
+            return;
+        }
+    }
+}
+
+void TestWaylandConnectionThread::cleanup()
+{
+    // terminates weston
+    m_westonProcess->terminate();
+    QVERIFY(m_westonProcess->waitForFinished());
+    delete m_westonProcess;
+    m_westonProcess = nullptr;
+}
+
+void TestWaylandConnectionThread::testInitConnectionNoThread()
+{
+    if (m_westonProcess->state() != QProcess::Running) {
+        QSKIP("This test requires a running wayland server");
+    }
+    QScopedPointer<KWin::Wayland::ConnectionThread> connection(new KWin::Wayland::ConnectionThread);
+    QCOMPARE(connection->socketName(), QStringLiteral("wayland-0"));
+    connection->setSocketName(s_socketName);
+    QCOMPARE(connection->socketName(), s_socketName);
+
+    QSignalSpy connectedSpy(connection.data(), SIGNAL(connected()));
+    QSignalSpy failedSpy(connection.data(), SIGNAL(failed()));
+    connection->initConnection();
+    QVERIFY(connectedSpy.wait());
+    QCOMPARE(connectedSpy.count(), 1);
+    QCOMPARE(failedSpy.count(), 0);
+    QVERIFY(connection->display());
+}
+
+void TestWaylandConnectionThread::testConnectionFailure()
+{
+    if (m_westonProcess->state() != QProcess::Running) {
+        QSKIP("This test requires a running wayland server");
+    }
+    QScopedPointer<KWin::Wayland::ConnectionThread> connection(new KWin::Wayland::ConnectionThread);
+    connection->setSocketName(QStringLiteral("kwin-test-socket-does-not-exist"));
+
+    QSignalSpy connectedSpy(connection.data(), SIGNAL(connected()));
+    QSignalSpy failedSpy(connection.data(), SIGNAL(failed()));
+    connection->initConnection();
+    QVERIFY(failedSpy.wait());
+    QCOMPARE(connectedSpy.count(), 0);
+    QCOMPARE(failedSpy.count(), 1);
+    QVERIFY(!connection->display());
+}
+
+static void registryHandleGlobal(void *data, struct wl_registry *registry,
+                                 uint32_t name, const char *interface, uint32_t version)
+{
+    Q_UNUSED(data)
+    Q_UNUSED(registry)
+    Q_UNUSED(name)
+    Q_UNUSED(interface)
+    Q_UNUSED(version)
+}
+
+static void registryHandleGlobalRemove(void *data, struct wl_registry *registry, uint32_t name)
+{
+    Q_UNUSED(data)
+    Q_UNUSED(registry)
+    Q_UNUSED(name)
+}
+
+static const struct wl_registry_listener s_registryListener = {
+    registryHandleGlobal,
+    registryHandleGlobalRemove
+};
+
+void TestWaylandConnectionThread::testConnectionThread()
+{
+    if (m_westonProcess->state() != QProcess::Running) {
+        QSKIP("This test requires a running wayland server");
+    }
+    QScopedPointer<KWin::Wayland::ConnectionThread> connection(new KWin::Wayland::ConnectionThread);
+    connection->setSocketName(s_socketName);
+
+    QThread *connectionThread = new QThread(this);
+    connection->moveToThread(connectionThread);
+    connectionThread->start();
+
+    QSignalSpy connectedSpy(connection.data(), SIGNAL(connected()));
+    QSignalSpy failedSpy(connection.data(), SIGNAL(failed()));
+    connection->initConnection();
+    QVERIFY(connectedSpy.wait());
+    QCOMPARE(connectedSpy.count(), 1);
+    QCOMPARE(failedSpy.count(), 0);
+    QVERIFY(connection->display());
+
+    // now we have the connection ready, let's get some events
+    QSignalSpy eventsSpy(connection.data(), SIGNAL(eventsRead()));
+    wl_display *display = connection->display();
+    wl_event_queue *queue = wl_display_create_queue(display);
+
+    wl_registry *registry = wl_display_get_registry(display);
+    wl_proxy_set_queue((wl_proxy*)registry, queue);
+
+    wl_registry_add_listener(registry, &s_registryListener, this);
+    wl_display_flush(display);
+
+    QVERIFY(eventsSpy.wait());
+
+    wl_registry_destroy(registry);
+    wl_event_queue_destroy(queue);
+
+    connectionThread->quit();
+    connectionThread->wait();
+    delete connectionThread;
+}
+
+void TestWaylandConnectionThread::testConnectionDieing()
+{
+    if (m_westonProcess->state() != QProcess::Running) {
+        QSKIP("This test requires a running wayland server");
+    }
+    QScopedPointer<KWin::Wayland::ConnectionThread> connection(new KWin::Wayland::ConnectionThread);
+    QSignalSpy connectedSpy(connection.data(), SIGNAL(connected()));
+    connection->setSocketName(s_socketName);
+    connection->initConnection();
+    QVERIFY(connectedSpy.wait());
+    QVERIFY(connection->display());
+
+    QSignalSpy diedSpy(connection.data(), SIGNAL(connectionDied()));
+    m_westonProcess->terminate();
+    QVERIFY(m_westonProcess->waitForFinished());
+    QVERIFY(diedSpy.wait());
+    QCOMPARE(diedSpy.count(), 1);
+    QVERIFY(!connection->display());
+
+    connectedSpy.clear();
+    QVERIFY(connectedSpy.isEmpty());
+    // restarts the server
+    delete m_westonProcess;
+    m_westonProcess = nullptr;
+    init();
+    if (connectedSpy.count() == 0) {
+        QVERIFY(connectedSpy.wait());
+    }
+    QCOMPARE(connectedSpy.count(), 1);
+}
+
+QTEST_MAIN(TestWaylandConnectionThread)
+#include "test_wayland_connection_thread.moc"

composite.cpp

@@ -113,14 +113,16 @@ Compositor::Compositor(QObject* workspace)
     if (kwinApp()->operationMode() != Application::OperationModeX11) {
         connect(Wayland::WaylandBackend::self(), &Wayland::WaylandBackend::systemCompositorDied, this, &Compositor::finish);
         connect(Wayland::WaylandBackend::self(), &Wayland::WaylandBackend::backendReady, this, &Compositor::setup);
-    }
+    } else
 #endif
 
+    {
     // delay the call to setup by one event cycle
     // The ctor of this class is invoked from the Workspace ctor, that means before
     // Workspace is completely constructed, so calling Workspace::self() would result
     // in undefined behavior. This is fixed by using a delayed invocation.
     QMetaObject::invokeMethod(this, "setup", Qt::QueuedConnection);
+    }
 
     // register DBus
     new CompositorDBusInterface(this);

main_wayland.cpp

@@ -90,10 +90,12 @@ void ApplicationWayland::performStartup()
 
     // try creating the Wayland Backend
     Wayland::WaylandBackend *backend = Wayland::WaylandBackend::create();
-    if (!backend) {
-        fputs(i18n("kwin_wayland: could not connect to Wayland Server, ensure WAYLAND_DISPLAY is set.\n").toLocal8Bit().constData(), stderr);
-        ::exit(1);
-    }
+    connect(backend, &Wayland::WaylandBackend::connectionFailed, this,
+        [] () {
+            fputs(i18n("kwin_wayland: could not connect to Wayland Server, ensure WAYLAND_DISPLAY is set.\n").toLocal8Bit().constData(), stderr);
+            ::exit(1);
+        }
+    );
 
     createWorkspace();
 

wayland_backend.cpp

@@ -22,12 +22,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // KWin
 #include "cursor.h"
 #include "input.h"
+#include "wayland_client/connection_thread.h"
 // Qt
 #include <QDebug>
 #include <QImage>
-#include <QFileSystemWatcher>
-#include <QSocketNotifier>
 #include <QTemporaryFile>
+#include <QThread>
 // xcb
 #include <xcb/xtest.h>
 #include <xcb/xfixes.h>
@@ -726,17 +726,13 @@ WaylandBackend *WaylandBackend::create(QObject *parent)
         return NULL;
     }
     s_self = new WaylandBackend(parent);
-    // check whether it has a display
-    if (!s_self->display()) {
-        delete s_self;
-        s_self = nullptr;
-    }
     return s_self;
 }
 
 WaylandBackend::WaylandBackend(QObject *parent)
     : QObject(parent)
     , m_display(nullptr)
+    , m_eventQueue(nullptr)
     , m_registry(nullptr)
     , m_compositor(NULL)
     , m_shell(NULL)
@@ -745,15 +741,9 @@ WaylandBackend::WaylandBackend(QObject *parent)
     , m_shellSurfaceSize(displayWidth(), displayHeight())
     , m_seat()
     , m_shm()
-    , m_systemCompositorDied(false)
-    , m_runtimeDir(qgetenv("XDG_RUNTIME_DIR"))
-    , m_socketWatcher(nullptr)
+    , m_connectionThreadObject(nullptr)
+    , m_connectionThread(nullptr)
 {
-    m_socketName = qgetenv("WAYLAND_DISPLAY");
-    if (m_socketName.isEmpty()) {
-        m_socketName = QStringLiteral("wayland-0");
-    }
-
     initConnection();
 }
 
@@ -775,10 +765,13 @@ WaylandBackend::~WaylandBackend()
     if (m_registry) {
         wl_registry_destroy(m_registry);
     }
-    if (m_display) {
-        wl_display_flush(m_display);
-        wl_display_disconnect(m_display);
-    }
+    m_seat.reset();
+    m_shm.reset();
+
+    m_connectionThreadObject->deleteLater();
+    m_connectionThread->quit();
+    m_connectionThread->wait();
+
     qDebug() << "Destroyed Wayland display";
     s_self = NULL;
 }
@@ -791,91 +784,67 @@ void WaylandBackend::destroyOutputs()
 
 void WaylandBackend::initConnection()
 {
-    m_display = wl_display_connect(nullptr);
-    if (!m_display) {
-        // TODO: maybe we should now really tear down
-        qWarning() << "Failed connecting to Wayland display";
-        return;
-    }
-    m_registry = wl_display_get_registry(m_display);
-    // setup the registry
-    wl_registry_add_listener(m_registry, &s_registryListener, this);
-    wl_display_dispatch(m_display);
-    int fd = wl_display_get_fd(m_display);
-    QSocketNotifier *notifier = new QSocketNotifier(fd, QSocketNotifier::Read, this);
-    connect(notifier, &QSocketNotifier::activated, this, &WaylandBackend::readEvents);
+    m_connectionThreadObject = new ConnectionThread(nullptr);
+    connect(m_connectionThreadObject, &ConnectionThread::connected, this,
+        [this]() {
+            // create the event queue for the main gui thread
+            m_display = m_connectionThreadObject->display();
+            m_eventQueue = wl_display_create_queue(m_display);
+            // setup registry
+            m_registry = wl_display_get_registry(m_display);
+            wl_proxy_set_queue((wl_proxy*)m_registry, m_eventQueue);
+            // setup the registry
+            wl_registry_add_listener(m_registry, &s_registryListener, this);
+            wl_display_flush(m_display);
+        },
+        Qt::QueuedConnection);
+    connect(m_connectionThreadObject, &ConnectionThread::eventsRead, this,
+        [this]() {
+            if (!m_eventQueue) {
+                return;
+            }
+            wl_display_dispatch_queue_pending(m_display, m_eventQueue);
+            wl_display_flush(m_display);
+        },
+        Qt::QueuedConnection);
+    connect(m_connectionThreadObject, &ConnectionThread::connectionDied, this,
+        [this]() {
+            emit systemCompositorDied();
+            m_seat.reset();
+            m_shm.reset();
+            destroyOutputs();
+            if (m_shellSurface) {
+                free(m_shellSurface);
+                m_shellSurface = nullptr;
+            }
+            if (m_surface) {
+                free(m_surface);
+                m_surface = nullptr;
+            }
+            if (m_shell) {
+                free(m_shell);
+                m_shell = nullptr;
+            }
+            if (m_compositor) {
+                free(m_compositor);
+                m_compositor = nullptr;
+            }
+            if (m_registry) {
+                free(m_registry);
+                m_registry = nullptr;
+            }
+            if (m_display) {
+                m_display = nullptr;
+            }
+        },
+        Qt::QueuedConnection);
+    connect(m_connectionThreadObject, &ConnectionThread::failed, this, &WaylandBackend::connectionFailed, Qt::QueuedConnection);
 
-    if (m_runtimeDir.exists()) {
-        m_socketWatcher = new QFileSystemWatcher(this);
-        m_socketWatcher->addPath(m_runtimeDir.absoluteFilePath(m_socketName));
-        connect(m_socketWatcher, &QFileSystemWatcher::fileChanged, this, &WaylandBackend::socketFileChanged);
-    }
-    qDebug() << "Created Wayland display";
-}
+    m_connectionThread = new QThread(this);
+    m_connectionThreadObject->moveToThread(m_connectionThread);
+    m_connectionThread->start();
 
-void WaylandBackend::readEvents()
-{
-    // TODO: this still seems to block
-    if (m_systemCompositorDied) {
-        return;
-    }
-    wl_display_flush(m_display);
-    wl_display_dispatch(m_display);
-}
-
-void WaylandBackend::socketFileChanged(const QString &socket)
-{
-    if (!QFile::exists(socket) && !m_systemCompositorDied) {
-        qDebug() << "We lost the system compositor at:" << socket;
-        m_systemCompositorDied = true;
-        emit systemCompositorDied();
-        m_seat.reset();
-        m_shm.reset();
-        destroyOutputs();
-        if (m_shellSurface) {
-            free(m_shellSurface);
-            m_shellSurface = nullptr;
-        }
-        if (m_surface) {
-            free(m_surface);
-            m_surface = nullptr;
-        }
-        if (m_shell) {
-            free(m_shell);
-            m_shell = nullptr;
-        }
-        if (m_compositor) {
-            free(m_compositor);
-            m_compositor = nullptr;
-        }
-        if (m_registry) {
-            free(m_registry);
-            m_registry = nullptr;
-        }
-        if (m_display) {
-            free(m_display);
-            m_display = nullptr;
-        }
-        // need a new filesystem watcher
-        delete m_socketWatcher;
-        m_socketWatcher = new QFileSystemWatcher(this);
-        m_socketWatcher->addPath(m_runtimeDir.absolutePath());
-        connect(m_socketWatcher, &QFileSystemWatcher::directoryChanged, this, &WaylandBackend::socketDirectoryChanged);
-    }
-}
-
-void WaylandBackend::socketDirectoryChanged()
-{
-    if (!m_systemCompositorDied) {
-        return;
-    }
-    if (m_runtimeDir.exists(m_socketName)) {
-        qDebug() << "Socket reappeared";
-        delete m_socketWatcher;
-        m_socketWatcher = nullptr;
-        initConnection();
-        m_systemCompositorDied = false;
-    }
+    m_connectionThreadObject->initConnection();
 }
 
 void WaylandBackend::createSeat(uint32_t name)
@@ -946,7 +915,7 @@ void WaylandBackend::addOutput(wl_output *o)
 
 void WaylandBackend::dispatchEvents()
 {
-    wl_display_dispatch_pending(m_display);
+    // TODO: integrate into event loop to flush before going to block
     wl_display_flush(m_display);
 }
 

wayland_backend.h

@@ -33,10 +33,10 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 class QTemporaryFile;
 class QImage;
-class QFileSystemWatcher;
 struct wl_cursor_theme;
 struct wl_buffer;
 struct wl_shm;
+struct wl_event_queue;
 
 namespace KWin
 {
@@ -46,6 +46,7 @@ namespace Wayland
 class ShmPool;
 class WaylandBackend;
 class WaylandSeat;
+class ConnectionThread;
 
 class CursorData
 {
@@ -233,15 +234,13 @@ Q_SIGNALS:
     void systemCompositorDied();
     void backendReady();
     void outputsChanged();
-private Q_SLOTS:
-    void readEvents();
-    void socketFileChanged(const QString &socket);
-    void socketDirectoryChanged();
+    void connectionFailed();
 private:
     void initConnection();
     void createSurface();
     void destroyOutputs();
     wl_display *m_display;
+    wl_event_queue *m_eventQueue;
     wl_registry *m_registry;
     wl_compositor *m_compositor;
     wl_shell *m_shell;
@@ -250,11 +249,9 @@ private:
     QSize m_shellSurfaceSize;
     QScopedPointer<WaylandSeat> m_seat;
     QScopedPointer<ShmPool> m_shm;
-    bool m_systemCompositorDied;
-    QString m_socketName;
-    QDir m_runtimeDir;
-    QFileSystemWatcher *m_socketWatcher;
     QList<Output*> m_outputs;
+    ConnectionThread *m_connectionThreadObject;
+    QThread *m_connectionThread;
 
     KWIN_SINGLETON(WaylandBackend)
 };

wayland_client/connection_thread.cpp

@@ -0,0 +1,146 @@
+/********************************************************************
+ KWin - the KDE window manager
+ This file is part of the KDE project.
+
+Copyright (C) 2014 Martin Gräßlin <mgraesslin@kde.org>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*********************************************************************/
+#include "connection_thread.h"
+// Qt
+#include <QDebug>
+#include <QFileSystemWatcher>
+#include <QSocketNotifier>
+// Wayland
+#include <wayland-client-protocol.h>
+
+namespace KWin
+{
+
+namespace Wayland
+{
+
+ConnectionThread::ConnectionThread(QObject *parent)
+    : QObject(parent)
+    , m_display(nullptr)
+    , m_socketName(QString::fromUtf8(qgetenv("WAYLAND_DISPLAY")))
+    , m_runtimeDir(QString::fromUtf8(qgetenv("XDG_RUNTIME_DIR")))
+    , m_socketNotifier(nullptr)
+    , m_socketWatcher(nullptr)
+    , m_serverDied(false)
+{
+    if (m_socketName.isEmpty()) {
+        m_socketName = QStringLiteral("wayland-0");
+    }
+}
+
+ConnectionThread::~ConnectionThread()
+{
+    if (m_display) {
+        wl_display_flush(m_display);
+        wl_display_disconnect(m_display);
+    }
+}
+
+void ConnectionThread::initConnection()
+{
+    QMetaObject::invokeMethod(this, "doInitConnection", Qt::QueuedConnection);
+}
+
+void ConnectionThread::doInitConnection()
+{
+    m_display = wl_display_connect(m_socketName.toUtf8().constData());
+    if (!m_display) {
+        qWarning() << "Failed connecting to Wayland display";
+        emit failed();
+        return;
+    }
+    qDebug() << "Connected to Wayland server at:" << m_socketName;
+
+    // setup socket notifier
+    setupSocketNotifier();
+    setupSocketFileWatcher();
+    emit connected();
+}
+
+void ConnectionThread::setupSocketNotifier()
+{
+    const int fd = wl_display_get_fd(m_display);
+    m_socketNotifier = new QSocketNotifier(fd, QSocketNotifier::Read, this);
+    connect(m_socketNotifier, &QSocketNotifier::activated, this,
+        [this]() {
+            if (!m_display) {
+                return;
+            }
+            wl_display_dispatch(m_display);
+            emit eventsRead();
+        }
+    );
+}
+
+void ConnectionThread::setupSocketFileWatcher()
+{
+    if (!m_runtimeDir.exists()) {
+        return;
+    }
+    m_socketWatcher = new QFileSystemWatcher(this);
+    m_socketWatcher->addPath(m_runtimeDir.absoluteFilePath(m_socketName));
+    connect(m_socketWatcher, &QFileSystemWatcher::fileChanged, this,
+        [this] (const QString &file) {
+            if (QFile::exists(file) || m_serverDied) {
+                return;
+            }
+            qWarning() << "Connection to server went away";
+            m_serverDied = true;
+            if (m_display) {
+                free(m_display);
+                m_display = nullptr;
+            }
+            delete m_socketNotifier;
+            m_socketNotifier = nullptr;
+
+            // need a new filesystem watcher
+            delete m_socketWatcher;
+            m_socketWatcher = new QFileSystemWatcher(this);
+            m_socketWatcher->addPath(m_runtimeDir.absolutePath());
+            connect(m_socketWatcher, &QFileSystemWatcher::directoryChanged, this,
+                [this]() {
+                    if (!m_serverDied) {
+                        return;
+                    }
+                    if (m_runtimeDir.exists(m_socketName)) {
+                        qDebug() << "Socket reappeared";
+                        delete m_socketWatcher;
+                        m_socketWatcher = nullptr;
+                        m_serverDied = false;
+                        initConnection();
+                    }
+                }
+            );
+            emit connectionDied();
+        }
+    );
+}
+
+void ConnectionThread::setSocketName(const QString &socketName)
+{
+    if (m_display) {
+        // already initialized
+        return;
+    }
+    m_socketName = socketName;
+}
+
+}
+}

wayland_client/connection_thread.h

@@ -0,0 +1,109 @@
+/********************************************************************
+ KWin - the KDE window manager
+ This file is part of the KDE project.
+
+Copyright (C) 2014 Martin Gräßlin <mgraesslin@kde.org>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*********************************************************************/
+#ifndef KWIN_WAYLAND_CONNECTION_THREAD_H
+#define KWIN_WAYLAND_CONNECTION_THREAD_H
+
+#include <QObject>
+#include <QDir>
+
+struct wl_display;
+class QFileSystemWatcher;
+class QSocketNotifier;
+
+namespace KWin
+{
+namespace Wayland
+{
+
+class ConnectionThread : public QObject
+{
+    Q_OBJECT
+public:
+    explicit ConnectionThread(QObject *parent = nullptr);
+    virtual ~ConnectionThread();
+
+    wl_display *display();
+    /**
+     * @returns the name of the socket it connects to.
+     **/
+    const QString &socketName() const;
+    /**
+     * Sets the @p socketName to connect to.
+     * Only applies if called before calling initConnection.
+     * The default socket name is derived from environment variable WAYLAND_DISPLAY
+     * and if not set is hard coded to "wayland-0".
+     **/
+    void setSocketName(const QString &socketName);
+
+public Q_SLOTS:
+    void initConnection();
+
+Q_SIGNALS:
+    /**
+     * Emitted once a connection to a Wayland server is established.
+     * Normally emitted after invoking initConnection(), but might also be
+     * emitted after re-connecting to another server.
+     **/
+    void connected();
+    /**
+     * Emitted if connecting to a Wayland server failed.
+     **/
+    void failed();
+    /**
+     * Emitted whenever new events are ready to be read.
+     **/
+    void eventsRead();
+    /**
+     * Emitted if the Wayland server connection dies.
+     * If the socket reappears, it is tried to reconnect.
+     **/
+    void connectionDied();
+
+private Q_SLOTS:
+    void doInitConnection();
+
+private:
+    void setupSocketNotifier();
+    void setupSocketFileWatcher();
+    wl_display *m_display;
+    QString m_socketName;
+    QDir m_runtimeDir;
+    QSocketNotifier *m_socketNotifier;
+    QFileSystemWatcher *m_socketWatcher;
+    bool m_serverDied;
+};
+
+inline
+const QString &ConnectionThread::socketName() const
+{
+    return m_socketName;
+}
+
+inline
+wl_display *ConnectionThread::display()
+{
+    return m_display;
+}
+
+}
+}
+
+
+#endif