[x11] Check pending release when mapping

Summary:
 when unmap notify is followed by a map, the old Unmanaged will get released and never be managed again. by checking if there is a pending release operation, we can safely re-manage the window again.

BUG: 413350

Reviewers: #kwin, zzag

Reviewed By: #kwin, zzag

Subscribers: zzag, kwin, scao

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D24878

events.cpp

@@ -328,8 +328,17 @@ bool Workspace::workspaceEvent(xcb_generic_event_t *e)
             Unmanaged* c = findUnmanaged(event->window);
             if (c == nullptr)
                 c = createUnmanaged(event->window);
-            if (c)
+            if (c) {
-                return c->windowEvent(e);
+                // if hasScheduledRelease is true, it means a unamp and map sequence has occurred. 
+                // since release is scheduled after map notify, this old Unmanaged will get released
+                // before KWIN has chance to remanage it again. so release it right now.
+                if (c->hasScheduledRelease()) {
+                    c->release();
+                    c = createUnmanaged(event->window);
+                }
+                if (c)
+                    return c->windowEvent(e);
+            }
         }
         return (event->event != event->window);   // hide wm typical event from Qt
     }
@@ -1265,6 +1274,7 @@ bool Unmanaged::windowEvent(xcb_generic_event_t *e)
         // short enough to not cause problems in the close window animations.
         // It's of course still possible that we miss the destroy in which case non-fatal
         // X errors are reported to the event loop and logged by Qt.
+        m_scheduledRelease = true;
         QTimer::singleShot(1, this, SLOT(release()));
         break;
     }

unmanaged.cpp

@@ -123,6 +123,11 @@ void Unmanaged::deleteUnmanaged(Unmanaged* c)
     delete c;
 }
 
+bool Unmanaged::hasScheduledRelease() const
+{
+    return m_scheduledRelease;
+}
+
 int Unmanaged::desktop() const
 {
     return NET::OnAllDesktops; // TODO for some window types should be the current desktop?

unmanaged.h

@@ -36,6 +36,7 @@ public:
     explicit Unmanaged();
     bool windowEvent(xcb_generic_event_t *e);
     bool track(xcb_window_t w);
+    bool hasScheduledRelease() const;
     static void deleteUnmanaged(Unmanaged* c);
     int desktop() const override;
     QStringList activities() const override;
@@ -62,6 +63,7 @@ private:
     void configureNotifyEvent(xcb_configure_notify_event_t *e);
     QWindow *findInternalWindow() const;
     bool m_outline = false;
+    bool m_scheduledRelease = false;
 };
 
 } // namespace