Fix BadWindow X11 errors when a window is closed while processing struts

A window can be closed on the server side while processing results from
_NET_CLIENT_LIST, which causes BadWindow fatal errors by default in
XGetWindowProperty.

The only way to safely catch this case is to set an error handler to
ignore BadWindow errors while these commands are processed.

1 files changed, 21 insertions, 2 deletions

diff --git a/platform/linuxbsd/display_server_x11.cpp b/platform/linuxbsd/display_server_x11.cpp
index e98d114267..c4e828bdb2 100644
--- a/platform/linuxbsd/display_server_x11.cpp
+++ b/platform/linuxbsd/display_server_x11.cpp
@@ -733,6 +733,16 @@ Size2i DisplayServerX11::screen_get_size(int p_screen) const {
 	return _screen_get_rect(p_screen).size;
 }
 
+bool g_bad_window = false;
+int bad_window_error_handler(Display *display, XErrorEvent *error) {
+	if (error->error_code == BadWindow) {
+		g_bad_window = true;
+	} else {
+		ERR_PRINT("Unhandled XServer error code: " + itos(error->error_code));
+	}
+	return 0;
+}
+
 Rect2i DisplayServerX11::screen_get_usable_rect(int p_screen) const {
 	_THREAD_SAFE_METHOD_
 
@@ -869,7 +879,13 @@ Rect2i DisplayServerX11::screen_get_usable_rect(int p_screen) const {
 					if (desktop_valid) {
 						use_simple_method = false;
 
+						// Handle bad window errors silently because there's no other way to check
+						// that one of the windows has been destroyed in the meantime.
+						int (*oldHandler)(Display *, XErrorEvent *) = XSetErrorHandler(&bad_window_error_handler);
+
 						for (unsigned long win_index = 0; win_index < clients_len; ++win_index) {
+							g_bad_window = false;
+
 							// Remove strut size from desktop size to get a more accurate result.
 							bool strut_found = false;
 							unsigned long strut_len = 0;
@@ -881,7 +897,7 @@ Rect2i DisplayServerX11::screen_get_usable_rect(int p_screen) const {
 								}
 							}
 							// Fallback to older strut property.
-							if (!strut_found) {
+							if (!g_bad_window && !strut_found) {
 								Atom strut_prop = XInternAtom(x11_display, "_NET_WM_STRUT", True);
 								if (strut_prop != None) {
 									if (XGetWindowProperty(x11_display, windows_data[win_index], strut_prop, 0, LONG_MAX, False, XA_CARDINAL, &type, &format, &strut_len, &remaining, &strut_data) == Success) {
@@ -889,7 +905,7 @@ Rect2i DisplayServerX11::screen_get_usable_rect(int p_screen) const {
 									}
 								}
 							}
-							if (strut_found && (format == 32) && (strut_len >= 4) && strut_data) {
+							if (!g_bad_window && strut_found && (format == 32) && (strut_len >= 4) && strut_data) {
 								long *struts = (long *)strut_data;
 
 								long left = struts[0];
@@ -961,6 +977,9 @@ Rect2i DisplayServerX11::screen_get_usable_rect(int p_screen) const {
 								XFree(strut_data);
 							}
 						}
+
+						// Restore default error handler.
+						XSetErrorHandler(oldHandler);
 					}
 				}
 			}