x11: Let selection input streams create their own window

When there are two (or more) concurrent XConvertSelection requests with
the same target, selection and window and the data is large enough for
SelectionNotify events to overlap. This can result in the affected streams
being considered completed without any data being transferred.

While regular mutter/shell code does not make use of concurrent
XConvertSelection requests with the same targets, some extensions might.
Such as for example a clipboard manager that like the built-in clipboard
manager tries to read the selection on owner-changed.

One potential solution would be to make sure the event is for the correct
property, but not all clients seem to support concurrent requests for the
same targets but different properties on the same window.

This commit instead changes the streams to use their own window which
seems to be more widely supported.

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/4034

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1812>

3 files changed, 17 insertions, 6 deletions

diff --git a/src/x11/meta-selection-source-x11.c b/src/x11/meta-selection-source-x11.c
index c9fc8fbc6..15f46a144 100644
--- a/src/x11/meta-selection-source-x11.c
+++ b/src/x11/meta-selection-source-x11.c
@@ -92,7 +92,6 @@ meta_selection_source_x11_read_async (MetaSelectionSource *source,
     mimetype = "UTF8_STRING";
 
   meta_x11_selection_input_stream_new_async (source_x11->x11_display,
-                                             source_x11->x11_display->selection.xwindow,
                                              gdk_x11_get_xatom_name (source_x11->xselection),
                                              mimetype,
                                              source_x11->timestamp,
@@ -251,7 +250,6 @@ meta_selection_source_x11_new_async (MetaX11Display      *x11_display,
   g_task_set_task_data (task, source, g_object_unref);
 
   meta_x11_selection_input_stream_new_async (x11_display,
-                                             x11_display->selection.xwindow,
                                              gdk_x11_get_xatom_name (xselection),
                                              "TARGETS",
                                              timestamp,
diff --git a/src/x11/meta-x11-selection-input-stream-private.h b/src/x11/meta-x11-selection-input-stream-private.h
index 3fcf9ffd1..a2b74ea99 100644
--- a/src/x11/meta-x11-selection-input-stream-private.h
+++ b/src/x11/meta-x11-selection-input-stream-private.h
@@ -33,7 +33,6 @@ G_DECLARE_FINAL_TYPE (MetaX11SelectionInputStream,
                       GInputStream)
 
 void           meta_x11_selection_input_stream_new_async     (MetaX11Display             *x11_display,
-                                                              Window                      window,
                                                               const char                 *selection,
                                                               const char                 *target,
                                                               guint32                     timestamp,
diff --git a/src/x11/meta-x11-selection-input-stream.c b/src/x11/meta-x11-selection-input-stream.c
index 74552679f..8a1318a89 100644
--- a/src/x11/meta-x11-selection-input-stream.c
+++ b/src/x11/meta-x11-selection-input-stream.c
@@ -287,6 +287,7 @@ meta_x11_selection_input_stream_finalize (GObject *object)
     META_X11_SELECTION_INPUT_STREAM (object);
   MetaX11SelectionInputStreamPrivate *priv =
     meta_x11_selection_input_stream_get_instance_private (stream);
+  Display *xdisplay = priv->x11_display->xdisplay;
 
   g_async_queue_unref (priv->chunks);
 
@@ -294,6 +295,8 @@ meta_x11_selection_input_stream_finalize (GObject *object)
   g_free (priv->target);
   g_free (priv->property);
 
+  XDestroyWindow (xdisplay, priv->window);
+
   G_OBJECT_CLASS (meta_x11_selection_input_stream_parent_class)->finalize (object);
 }
 
@@ -504,7 +507,6 @@ meta_x11_selection_input_stream_xevent (MetaX11SelectionInputStream *stream,
 
 void
 meta_x11_selection_input_stream_new_async (MetaX11Display      *x11_display,
-                                           Window               window,
                                            const char          *selection,
                                            const char          *target,
                                            guint32              timestamp,
@@ -515,10 +517,14 @@ meta_x11_selection_input_stream_new_async (MetaX11Display      *x11_display,
 {
   MetaX11SelectionInputStream *stream;
   MetaX11SelectionInputStreamPrivate *priv;
+  XSetWindowAttributes attributes = { 0 };
 
   stream = g_object_new (META_TYPE_X11_SELECTION_INPUT_STREAM, NULL);
   priv = meta_x11_selection_input_stream_get_instance_private (stream);
 
+  attributes.event_mask = PropertyChangeMask;
+  attributes.override_redirect = True;
+
   priv->x11_display = x11_display;
   x11_display->selection.input_streams =
     g_list_prepend (x11_display->selection.input_streams, stream);
@@ -528,13 +534,21 @@ meta_x11_selection_input_stream_new_async (MetaX11Display      *x11_display,
   priv->xtarget = XInternAtom (x11_display->xdisplay, priv->target, False);
   priv->property = g_strdup_printf ("META_SELECTION_%p", stream);
   priv->xproperty = XInternAtom (x11_display->xdisplay, priv->property, False);
-  priv->window = window;
+  priv->window = XCreateWindow (x11_display->xdisplay,
+                                x11_display->xroot,
+                                -1, -1, 1, 1,
+                                0, /* border width */
+                                0, /* depth */
+                                InputOnly, /* class */
+                                CopyFromParent, /* visual */
+                                CWEventMask | CWOverrideRedirect,
+                                &attributes);
 
   XConvertSelection (x11_display->xdisplay,
                      priv->xselection,
                      priv->xtarget,
                      priv->xproperty,
-                     window,
+                     priv->window,
                      timestamp);
 
   priv->pending_task = g_task_new (NULL, cancellable, callback, user_data);