Introduce path for surviving compositor restarts

This patch introduces an optional mechanism for clients to survive a
crash and reconnect seemingly seamlessly.

In the event of a disconnect from the compositor socket we simply try to
reconnect again and replay any data needed so that we maintain a
consistent state to where we left off.

From an application point-of-view any open popups will be dismissed and
we we potentially get a new framecallback, but it will be almost
entirely transparent. Users of custom QWaylandClientExtensions will be
notified via the activeChanged signal and rebuild as though the
compositor had withdrawn and re-announced the global.

OpenGL contexts will be marked as invalid, and handled the same way as a
GPU reset. On the next frame RHI will notice these are invalid and
recreate them, only now against a new wl_display and new EGLDisplay.

Users of low level EGL/native objects might be affected, but the
alternative at this point is being closed anyway. The entire codepath is
only activated via an environment variable.

Change-Id: I6c4acc885540e14cead7640794df86dd974fef4f
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

1 files changed, 12 insertions, 1 deletions

diff --git a/src/client/qwaylandshmbackingstore.cpp b/src/client/qwaylandshmbackingstore.cpp
index b9bfc9c81..779ee45c7 100644
--- a/src/client/qwaylandshmbackingstore.cpp
+++ b/src/client/qwaylandshmbackingstore.cpp
@@ -136,7 +136,18 @@ QWaylandShmBackingStore::QWaylandShmBackingStore(QWindow *window, QWaylandDispla
     : QPlatformBackingStore(window)
     , mDisplay(display)
 {
-
+    QObject::connect(mDisplay, &QWaylandDisplay::reconnected, window, [this]() {
+        auto copy = mBuffers;
+        // clear available buffers so we create new ones
+        // actual deletion is deferred till after resize call so we can copy
+        // contents from the back buffer
+        mBuffers.clear();
+        mFrontBuffer = nullptr;
+        // resize always resets mBackBuffer
+        if (mRequestedSize.isValid() && waylandWindow())
+            resize(mRequestedSize);
+        qDeleteAll(copy);
+    });
 }
 
 QWaylandShmBackingStore::~QWaylandShmBackingStore()