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Prevent tilemap editor hang and crash by mutex guarding tile_map_layer dirty.cell_list. #87458

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Prevent tilemap editor hang and crash by mutex guarding tile_map_layer dirty.cell_list. #87458

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5 changes: 4 additions & 1 deletion scene/2d/tile_map_layer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2111,6 +2111,8 @@ void TileMapLayer::notify_tile_map_change(DirtyFlags p_what) {
}

void TileMapLayer::internal_update() {
MutexLock lock(dirty.mutex);
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This lock might be too strict and cause performance problems, would need to be evaluated, it locks quite a large block of code, might be better to lock more specifically to the critical sections

CC @RandomShaper

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It basically just prevents set_cell from running during internal_update, which seemed pretty reasonable. ~all of the _ helper functions here can touch the dirty cell list, so it seemed pretty fairly scoped. I'm open to other ideas though.

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@AThousandShips AThousandShips Jan 22, 2024 •
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A lot of the stuff in those methods do things unrelated to it though, so unless those are also critical theras potential stuff there

Also unsure if this is the only affected list


// Find TileData that need a runtime modification.
// This may add cells to the dirty list is a runtime modification has been notified.
_build_runtime_update_tile_data();
Expand Down Expand Up @@ -2187,6 +2189,7 @@ void TileMapLayer::set_cell(const Vector2i &p_coords, int p_source_id, const Vec
c.alternative_tile = alternative_tile;

// Make the given cell dirty.
MutexLock lock(dirty.mutex);
if (!E->value.dirty_list_element.in_list()) {
dirty.cell_list.add(&(E->value.dirty_list_element));
}
Comment on lines +2192 to 2195
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Suggested change
MutexLock lock(dirty.mutex);
if (!E->value.dirty_list_element.in_list()) {
dirty.cell_list.add(&(E->value.dirty_list_element));
}
{
MutexLock lock(dirty.mutex);
if (!E->value.dirty_list_element.in_list()) {
dirty.cell_list.add(&(E->value.dirty_list_element));
}
}

I'd at least reduce this one, the rest should be looked into

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@AThousandShips AThousandShips Jan 22, 2024 •
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Though there is a possible race condition between this whole method and the update one, as it looks up an iterator in tile_map above which is touched by the update, I think this whole class needs some thread safety evaluation

The class itself isn't thread safe as such necessarily, as the scene tree isn't, so the consideration is really with the editor, it might rather be an issue to solve on the editor side as this does seem to be an editor issue, unsure if it pops up elsewhere (but then it's not really a big issue as this isn't guaranteed to be thread safe)

So this might rather be something to solve on the editor interface side, and that there's some threading going on in the tilemap editor that breaks here

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There is threading for the TileMap editor and specifically the pattern generation, I suspect this is what's causing this and might be the area to look into, rather than adding it to the TileMap itself, unsure how to handle that part specifically though

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@AThousandShips AThousandShips Jan 22, 2024 •
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I suspect this code is the problem:

godot/editor/plugins/tiles/tiles_editor_plugin.cpp

Lines 70 to 144 in 0bcc0e9

void TilesEditorUtils::_thread() {
pattern_thread_exited.clear();
while (!pattern_thread_exit.is_set()) {
pattern_preview_sem.wait();
pattern_preview_mutex.lock();
if (pattern_preview_queue.size() == 0) {
pattern_preview_mutex.unlock();
} else {
QueueItem item = pattern_preview_queue.front()->get();
pattern_preview_queue.pop_front();
pattern_preview_mutex.unlock();
int thumbnail_size = EDITOR_GET("filesystem/file_dialog/thumbnail_size");
thumbnail_size *= EDSCALE;
Vector2 thumbnail_size2 = Vector2(thumbnail_size, thumbnail_size);
if (item.pattern.is_valid() && !item.pattern->is_empty()) {
// Generate the pattern preview
SubViewport *viewport = memnew(SubViewport);
viewport->set_size(thumbnail_size2);
viewport->set_disable_input(true);
viewport->set_transparent_background(true);
viewport->set_update_mode(SubViewport::UPDATE_ONCE);
TileMap *tile_map = memnew(TileMap);
tile_map->set_tileset(item.tile_set);
tile_map->set_pattern(0, Vector2(), item.pattern);
viewport->add_child(tile_map);
TypedArray<Vector2i> used_cells = tile_map->get_used_cells(0);
Rect2 encompassing_rect;
encompassing_rect.set_position(tile_map->map_to_local(used_cells[0]));
for (int i = 0; i < used_cells.size(); i++) {
Vector2i cell = used_cells[i];
Vector2 world_pos = tile_map->map_to_local(cell);
encompassing_rect.expand_to(world_pos);
// Texture.
Ref<TileSetAtlasSource> atlas_source = item.tile_set->get_source(tile_map->get_cell_source_id(0, cell));
if (atlas_source.is_valid()) {
Vector2i coords = tile_map->get_cell_atlas_coords(0, cell);
int alternative = tile_map->get_cell_alternative_tile(0, cell);
if (atlas_source->has_tile(coords) && atlas_source->has_alternative_tile(coords, alternative)) {
Vector2 center = world_pos - atlas_source->get_tile_data(coords, alternative)->get_texture_origin();
encompassing_rect.expand_to(center - atlas_source->get_tile_texture_region(coords).size / 2);
encompassing_rect.expand_to(center + atlas_source->get_tile_texture_region(coords).size / 2);
}
}
}
Vector2 scale = thumbnail_size2 / MAX(encompassing_rect.size.x, encompassing_rect.size.y);
tile_map->set_scale(scale);
tile_map->set_position(-(scale * encompassing_rect.get_center()) + thumbnail_size2 / 2);
// Add the viewport at the last moment to avoid rendering too early.
callable_mp((Node *)EditorNode::get_singleton(), &Node::add_child).call_deferred(viewport, false, Node::INTERNAL_MODE_DISABLED);
RS::get_singleton()->connect(SNAME("frame_pre_draw"), callable_mp(const_cast<TilesEditorUtils *>(this), &TilesEditorUtils::_preview_frame_started), Object::CONNECT_ONE_SHOT);
pattern_preview_done.wait();
Ref<Image> image = viewport->get_texture()->get_image();
// Find the index for the given pattern. TODO: optimize.
item.callback.call(item.pattern, ImageTexture::create_from_image(image));
viewport->queue_free();
}
}
}
pattern_thread_exited.set();
}

But unsure how to approach it exactly, might work by adding a update_internals() after setting the pattern, or doing some other deferred operation here, will check if I can replicate the crash later today and see about this as a solution

Alternatively override a local call queue, will investigate

Expand Down Expand Up @@ -2939,4 +2942,4 @@ TerrainConstraint::TerrainConstraint(Ref<TileSet> p_tile_set, const Vector2i &p_
}
}
terrain = p_terrain;
}
}
1 change: 1 addition & 0 deletions scene/2d/tile_map_layer.h
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Original file line number Diff line number Diff line change
Expand Up @@ -262,6 +262,7 @@ class TileMapLayer : public Node2D {

// Dirty flag. Allows knowing what was modified since the last update.
struct {
Mutex mutex;
bool flags[DIRTY_FLAGS_MAX] = { false };
SelfList<CellData>::List cell_list;
} dirty;
Expand Down
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