CNA-BUG-087: Game::Dispose(true) walks Components by live index, so a component that removes itself or another during Dispose makes the loop skip one

CNA snapshot 009d40f5  ·  Known Issues › Current bugs  ·  source links pinned to 009d40f5

XNA 4.0 copies the collection to an array before disposing; CNA re-reads the count and indexes the live collection, so a removal during a component's Dispose shifts later entries and the next component is never disposed by that pass.

Identifier

CNA-BUG-087

Category

Bug

Subsystem

Core & runtime

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Severity

Low (a triage suggestion, not a project priority)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

None

Affected contract

Microsoft::Xna::Framework::Game::Dispose(bool)

Expected behaviour

XNA 4.0 (IL of Game.Dispose(bool)) copies Components into a new IGameComponent[] and disposes from the copy, which is needed because XNA's GameComponent.Dispose itself removes the component.

Actual behaviour at TARGET

Game.cpp loops for (i = 0; i < Components_.getCountProperty(); ++i) and disposes Components_[i]. If a component's Dispose removes itself (the XNA behaviour a port may re-implement, see CNA-BUG-086) or another component, every later entry shifts down one slot and the component that moved into slot i is skipped.

Source locations

• modules/runtime/src/Game.cpp — Game::Dispose(bool) component loop

Evidence

Checked by reading the named sources at 009d40f5; nothing was built or executed for this entry.

Focused reproduction

// Illustrative; not compiled or run for this entry.
class SelfRemoving : public GameComponent {
    using GameComponent::GameComponent;
protected:
    void Dispose(bool disposing) override {
        getGameProperty().getComponentsProperty().Remove(this);
        GameComponent::Dispose(disposing);
    }
};
// Components = { a (SelfRemoving), b }
// game.Dispose(): a is disposed and removed; b moves to index 0; i becomes 1; b is never disposed.

Current tests

No test disposes a Game whose components mutate the collection.

Regression test

A test with two components where the first removes itself in Dispose, asserting that both were disposed.

Blast radius

Games whose component Dispose overrides remove components (the XNA-faithful pattern). Games with passive components are unaffected.

Workaround

Do not mutate Components from a component's Dispose, or dispose components yourself before the Game.