[GTK4] UnsatisfiedLinkError in Display.flushExposes

[ptziegler]

Describe the bug

X11 only
When using the GTK4 port, trying to create multiple instances of a shell may lead to an error due to calling GTK3-exclusive methods.

To Reproduce

Create two or more instances of Snippet133. This issue doesn't happen all the time but should happen at some point.

Environment:

1. Select the platform(s) on which the behavior is seen:

• • All OS
• • Windows
• • Linux
• • macOS

Stacktrace:

Exception in thread "main" java.lang.UnsatisfiedLinkError: 'long org.eclipse.swt.internal.gtk.GDK.gdk_x11_window_lookup_for_display(long, long)'
	at org.eclipse.swt.internal.gtk.GDK.gdk_x11_window_lookup_for_display(Native Method)
	at org.eclipse.swt.widgets.Display.checkIfEventProc(Display.java:1026)
	at org.eclipse.swt.internal.gtk.OS.XCheckIfEvent(Native Method)
	at org.eclipse.swt.widgets.Display.flushExposes(Display.java:1735)
	at org.eclipse.swt.widgets.Control.update(Control.java:6791)
	at org.eclipse.swt.widgets.Shell.setVisible(Shell.java:3005)
	at org.eclipse.swt.widgets.Shell.open(Shell.java:2050)
	at org.eclipse.swt.snippets.Snippet133.open(Snippet133.java:95)
	at org.eclipse.swt.snippets.Snippet133.main(Snippet133.java:57)

[ptziegler]

As shown in the stacktrace, the issue is caused by calling gdk_x11_window_lookup_for_display as opposed to the (with 4.18 deprecated) gdk_x11_surface_lookup_for_display.

This method is used to invalidate a specific area of the window in order to force a repaint operation. But to my knowledge, this is not possible in GTK4; You can only redraw entire widgets, but not sub-sections.

My guess is we either need to call gdk_display_flush, gtk_widget_queue_draw or evaluate whether this is really needed in GTK4.

[ptziegler]

A guard was added as a result of Bug 577199 - [GTK4] Snippets do not launch while running on X11 due to GTK_IS_PLUG with the reasoning that GTK plugs are no longer supported in GTK4:

Gtk plugs are no longer supported in GTK4 thus any calls to GTK_IS_PLUG should only occur while not in a GTK4 environment.

However, given that the exception is thrown from within this block (line 3005), this guard seems to be insufficient.

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Shell.java

Lines 2979 to 3009 in 4a201e2

	if (!( !GTK.GTK4 && OS.isX11() && GTK.GTK_IS_PLUG (shellHandle))) {
	display.dispatchEvents = new int [] {
	GDK.GDK_EXPOSE,
	GDK.GDK_FOCUS_CHANGE,
	GDK.GDK_CONFIGURE,
	GDK.GDK_MAP,
	GDK.GDK_UNMAP,
	GDK.GDK_NO_EXPOSE,
	GDK.GDK_WINDOW_STATE
	};
	Display display = this.display;
	display.putGdkEvents();
	boolean iconic = false;
	Shell shell = parent != null ? parent.getShell() : null;
	do {
	if (GTK.GTK4) {
	OS.g_main_context_iteration (0, false);
	} else {
	GTK3.gtk_main_iteration_do (false);
	}
	if (isDisposed ()) break;
	iconic = minimized || (shell != null && shell.minimized);
	} while (!mapped && !iconic);
	display.dispatchEvents = null;
	if (isDisposed ()) return;
	if (!iconic) {
	update (true, true);
	if (isDisposed ()) return;
	adjustTrim (oldWidth, oldHeight);
	}
	}