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F17 — Threading probes ​

Deliberately violate each platform's threading rules and record exactly what breaks and how it manifests — error code, exception, deadlock, or silent corruption. Frameworks inherit their threading model from the strictest platform; this row supplies the evidence.

Requirements ​

Each probe is a separate run mode (--probe=N), each ending in a logged verdict (probe n=… result=ok|error|crash|deadlock|silent detail=…):

  1. Create a window off the main thread (events pumped on main):
    • macOS is the anchor: AppKit asserts/undefined behavior off the main thread — capture the exact console assert (NSWindow should only be instantiated on the main thread!?). Also probe with NSApplicationLoad-style legacy escape hatches absent.
    • Win32: legal — but the creating thread owns the message queue; prove GetMessage on the other thread receives its messages and the main thread does not.
    • X11: legal with XInitThreads() — probe with AND without it; record the corruption mode without (the classic async reply error).
    • Wayland: wl_display is thread-safe by design (per-thread event queues) — prove a second-thread wl_event_queue works; record the rules.
  2. Pump events on a non-creating thread (where distinguishable from probe 1).
  3. Render from a second thread while events flow on the main one: CPU-fill the buffer on a worker and present from it — Wayland (wl_surface.commit from worker with its own queue), X11 (XShmPutImage from worker, with XInitThreads), Win32 (BitBlt from a DC acquired on the worker), macOS (lockFocusIfCanDraw-free path: draw into a buffer + setNeedsDisplay marshaled vs direct CGContext access — record what the docs forbid vs what observably happens).
  4. Run every probe twice; flaky/probabilistic outcomes (race-dependent) must be marked result=nondeterministic with both observed outcomes.

WARNING

Crashes are expected outcomes here. Every probe must still exit through a handler that flushes the instrumentation log (install signal/SEH/uncaught-exception hooks), so the verdict line survives the crash.

Instrumentation ​

probe n=… thread=… action=… around every cross-thread call; the final verdict line per probe.

Findings to record ​

  • A platform × probe outcome table (this is the design-constraints.md threading section).
  • The exact failure artifacts (assert text, BadAccess-style codes, HRESULTs) with log excerpts.
  • The narrowest safe contract a framework can promise on all four platforms (expected: "create and pump on one designated thread; render anywhere with platform-specific ceremony" — verify or refute).

Verification ​

Wayland/X11: Tier A. Win32: A[wine] — but Wine's threading implementation diverges from real user32 internals; re-confirm any surprising Win32 outcome on real Windows (manual queue). macOS: A[ssh] — the assert-on-spawn outcomes don't need a visible window.