CNA-BUG-081: Game::InactiveSleepTime is stored and validated but the loop never sleeps while the game is inactive

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

InactiveSleepTime is documented in Game.hpp and the C API as how long the loop sleeps while the game is inactive, but nothing in Tick, RunLoop or the browser frame reads it, so an unfocused game keeps its full frame rate.

Identifier

CNA-BUG-081

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

Yes: see Current tests

Affected contract

Microsoft::Xna::Framework::Game::getInactiveSleepTimeProperty() / setInactiveSleepTimeProperty(); cna_game_get_inactive_sleep_time_ticks / cna_game_set_inactive_sleep_time_ticks

Expected behaviour

Game.hpp documents the property as “the time spent sleeping when the game is inactive”, and runtime.h as “how long the loop sleeps while the game is inactive”. XNA 4.0's Game.Tick sleeps for InactiveSleepTime whenever IsActive is false.

Actual behaviour at TARGET

InactiveSleepTime_ is initialised to 20 ms, rejected when negative (the message says “must be positive” although zero is accepted) and returned by the getter; no code reads it. Game::Tick and Game::RunLoop run at the target rate whether or not the window has focus. Only the mobile suspension path parks the thread, through WaitWhileSuspended and a fixed 16 ms delay. FNA stores the value and ignores it in the same way.

Source locations

• modules/runtime/src/Game.cpp — InactiveSleepTime_ initialisation, getInactiveSleepTimeProperty/setInactiveSleepTimeProperty; no reader in Tick, RunLoop or WaitWhileSuspended
• modules/runtime/include/Microsoft/Xna/Framework/Game.hpp — Doxygen of the InactiveSleepTime accessors
• modules/c-api/include/CNA/C/runtime.h — cna_game_get_inactive_sleep_time_ticks / cna_game_set_inactive_sleep_time_ticks documentation
• modules/c-api/src/CnaCApiGameProperties.cpp — C wrappers forward to the canonical accessors

Evidence

Checked by reading Game.cpp and searching every module at 009d40f5 for InactiveSleepTime: the only uses are the accessors and the C API wrappers. XNA 4.0's behaviour was read from the IL of Game.Tick. Not executed.

Independently observed as a separate finding (merged): XNA 4.0's Tick sleeps for InactiveSleepTime while the game is inactive; CNA's Tick, RunLoop and browser frame never read the value.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

No test in modules/runtime/tests reads or sets InactiveSleepTime. RuntimeGameSmoke.c round-trips the value and checks the negative-value refusal through the C API only (and the C library is not built in CI).

Regression test

A runtime test with a platform decorator that counts Delay() calls: deliver a focus-lost event, run one frame and expect a delay of InactiveSleepTime; with focus regained, expect none.

Blast radius

Desktop games that lose focus keep rendering and consuming CPU and GPU at full rate; code that sets the property (through C++ or the C API) gets no effect. Mobile suspension is handled separately and is unaffected.

Workaround

Check getIsActiveProperty() in Update and sleep or skip work while it is false, or subscribe to Deactivated/Activated.