Draft upstream report: Compiled Graph crashes on Windows¶

Status: retained draft only. This report has not been filed upstream.

Evidence limitation: the original Windows pass did not retain raw stdout/stderr or an exact dependency and runtime-profile inventory. Reproduce in a fresh disposable environment before filing; the current summary is not promotion-grade evidence.

Follow-up ownership: issue #100 owns the fresh Windows/nightly evidence and upstream report, targeted for 2026-07-27. It is non-blocking for issue #86 / PR #92 and for Linux/Kubernetes promotion work in issue #99.

Proposed title¶

[core][compiled graph][windows] experimental_compile crashes in shared-memory writer registration

Summary¶

On Windows 11 build 26200 AMD64 with CPython 3.12.12, a one-actor CPU Compiled Graph crashes while experimental_compile() registers its shared-memory writer. The same failure reproduces on Ray 2.53.0, 2.56.0, and 2.56.1.

• In a directly connected Ray Core driver, Python exits with 3221225477 (0xC0000005) after Windows fatal exception: access violation.
• When compilation is owned by a max_retries=0 outer Ray task, that worker crashes and the driver receives WorkerCrashedError.
• The captured stacks reach ray.experimental.channel.shared_memory_channel.ensure_registered_as_writer during DAGNode.experimental_compile().

The equivalent Linux candidate jobs are tracked separately. This report does not claim that every Windows, Python, Ray, or Compiled Graph topology is affected.

Environment¶

• Windows 11 build 26200, AMD64
• CPython 3.12.12
• Ray installed as ray[cgraph]==2.53.0, 2.56.0, or 2.56.1 in the repository virtual environment; the reproducer itself imports only Ray
• CPU shared-memory transport; no GPU or NCCL path
• Direct virtual-environment interpreter, not an environment-manager wrapper

Minimal reproduction¶

Use a fresh virtual environment for each Ray version. The standalone reproducer imports Ray only and supports one topology per process:

py -3.12 -m venv .venv
.venv\Scripts\python.exe -m pip install "ray[cgraph]==2.56.1"

# Run each command from a disposable shell under an external 60-second bound.
.venv\Scripts\python.exe docs\investigations\reproduce_ray_compiled_graph_windows.py `
  --topology direct-driver
.venv\Scripts\python.exe docs\investigations\reproduce_ray_compiled_graph_windows.py `
  --topology nested-ray-task

Repeat in clean environments for 2.53.0 and 2.56.0. The direct process may terminate before Python cleanup runs; do not run it inside an application or test worker.

Expected behavior¶

The graph compiles, echoes the payload once, drains the result, and tears down. If Windows is unsupported, compilation should fail with a normal, documented Python exception before native memory access rather than terminating the process or worker.

Observed results¶

The exact structured record, including the separately observed Linux control results, is retained in compiled-graph-platform-evidence-2026-07-19.json.

Nightly and issue search¶

Nightly was not run. Its wheel URL and ABI are a separate, rotating tuple, while this investigation was intended to classify exact published releases. A nightly result would not verify or invalidate any of the six release tuples above. It may be useful after maintainers identify a candidate fix.

Read-only searches of ray-project/ray on 2026-07-19 for ensure_registered_as_writer, Compiled Graph Windows access violation, and SharedMemoryChannel Windows returned no matching issue. Search results can change; repeat the search immediately before filing.

Issue #100 refresh, attachments, and maintainer questions¶

• Rerun the release and nightly tuples by 2026-07-27 in fresh disposable environments before deciding whether to file this draft. This is not a prerequisite for merging issue #86 / PR #92's fail-closed Linux/Kubernetes infrastructure.
• Attach the JSON record, exact dependency/runtime profile, and reviewed, redacted, bounded stdout/stderr tails from each disposable run. Never attach complete unredacted process output.
• Confirm whether CPU Compiled Graph is intended to support Windows.
• If not, can experimental_compile() fail before shared-memory channel setup?
• If yes, is writer registration missing a Windows-specific mapping or lifecycle step?