buildings_tools constantly creates new cursors causing XWayland to crash

[anonymous]

JOSM: 18389
buildings_tools: 35916

The problem is caused by buildings_tools plugin in JOSM – it generates a new cursor for every mouse movement while over the JOSM drawing area and every new cursor causes a new open file in Wayland eventually causing it to run out of file descriptors and crash.

How to reproduce in Gnome Wayland session:

1. Choose buildings_tools tool with "B".
2. Move cursor over JOSM drawing area.
3. See constant increase of open files in Gnome (Wayland): watch -n 1 -d 'ls -l /proc/`pidof gnome-shell`/fd/ | wc -l'.
4. Choose any other tool, e. g. with "W".
5. Move cursor over JOSM drawing area and see no open file increase.

More details about this problem on Wayland side: ​https://gitlab.freedesktop.org/xorg/xserver/-/issues/1306

Problem is probably caused by something in DrawBuildingAction.java updCursor():

    private void updCursor() {
        if (!MainApplication.isDisplayingMapView())
            return;

        if (!ctrl && (mousePos != null)) {
            Node n = MainApplication.getMap().mapView.getNearestNode(mousePos, OsmPrimitive::isSelectable);
            if (n != null) {
                setCursor(cursorJoinNode);
                return;
            } else {
                Way w = MainApplication.getMap().mapView.getNearestWay(mousePos, OsmPrimitive::isSelectable);
                if (w != null && w.get("building") != null) {
                    setCursor(cursorJoinWay);
                    return;
                }
            }
        }
        if (customCursor != null && (!ctrl || isRectDrawing()))
            setCursor(customCursor);
        else
            setCursor(getCursor());

    }

I tried to follow DevelopersGuide/DevelopingPlugins to debug this, but for some reason couldn't even checkout JOSM plugins repository over SVN (svn co https://josm.openstreetmap.de/osmsvn/applications/editors/josm – nothing happens for hours) and did not find a git mirror of this repository...

[taylor.smock]

Depending upon when you tried to clone the JOSM plugins repository, the server may have been down. See ​https://lists.openstreetmap.org/pipermail/josm-dev/2022-March/008420.html .

But thank you for an explanation of the problem -- I've been meaning to debug what is happening (I've run into this at home), and I just never got around to it.

[taylor.smock]

Other possible problem areas:

• ParallelWayAction​ (core, shift+p) Not a problem (tested)

[taylor.smock]

In 35929/osm:

fix #21929: buildings_tools creating unnecessary file descriptors

This causes XWayland to crash (Java uses XWayland at this time, when run under
Wayland). buildings_tools causes this problem by constantly creating new
cursors in the EDT thread.

[taylor.smock]

In 35930/osm:

buildings_tools (dist): see #21929: creating unnecessary file descriptors

This causes XWayland to crash (Java uses XWayland at this time, when run under
Wayland). buildings_tools causes this problem by constantly creating new
cursors in the EDT thread.