Fix: bind runner TLS during arena prewarm

[hashiqiqixian]

Summary

• bind the active DeviceRunner in thread-local storage for the full simpler_init() call
• clear the binding on every return path with RAIIScopeGuard
• prevent eager arena prewarming from dereferencing a null runner on sim and onboard
• add an in-repo a2a3sim TRB regression test for L2 Worker.init(prewarm_config=...)

Root cause

HostApi callbacks recover the current runner through thread-local storage. The eager prewarm path runs during simpler_init(), before the existing register/run entry points establish that binding.

Validation

• git diff --check
• clang-format --dry-run --Werror on both modified C++ files
• Python syntax validation for test_prewarm_config.py
• Simpler PR CI runs the new test under the existing a2a3sim scene-test job
• downstream PyPTO CI: bump pinned pto-isa to 96ba706c #2085 previously passed the five system jobs that crashed before the fix

A full local runtime rebuild was not run because the development host had only 3.07 GB available RAM; PR CI provides the runtime build and simulator execution.

Related

• perf(runtime): prewarm the runtime arena with a bound runner pypto#2085
• perf(runtime): prewarm the prebuilt runtime arena at worker init pypto#2068

[gemini-code-assist]

Code Review

This pull request updates the simpler_init function in both src/common/platform/onboard/host/c_api_shared.cpp and src/common/platform/sim/host/c_api_shared.cpp to establish a thread-local binding for the device runner (g_runner_key) using pthread_setspecific. It also introduces an RAII scope guard to ensure the thread-specific data is cleared upon exiting the function. There are no review comments to address, and I have no additional feedback to provide.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Initialization now scopes the provided device runner in thread-local storage for HostApi callbacks on onboard and simulator paths. A regression test covers L2 worker initialization with prewarm_config for the tensormap-and-ringbuffer runtime.

Changes

Prewarm runner binding

Layer / File(s)	Summary
Scoped runner binding src/common/platform/onboard/host/c_api_shared.cpp, src/common/platform/sim/host/c_api_shared.cpp	Initialization creates the pthread key once, binds the current runner for HostApi callbacks, and clears it through an RAII guard on exit.
Prewarm initialization regression test tests/st/a2a3/tensormap_and_ringbuffer/test_prewarm_config.py	Adds an A2A3 simulation test that initializes an L2 worker with ring_task_window = 64 and closes the worker in cleanup.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• hw-native-sys/simpler#1322: Also connects prewarm initialization with runner-aware HostApi callback dispatch.

Poem

A rabbit found a runner thread,
And bound it where the callbacks sped.
Prewarm configs now hop the ring,
While cleanup clips each dangling string.
Hop, hop—initialization sings!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title accurately summarizes the main change: binding runner TLS during arena prewarm.
Description check	✅ Passed	The description matches the code and test changes, including TLS binding, RAII cleanup, and the new regression test.

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[hashiqiqixian]

@coderabbitai review

[coderabbitai]

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[ChaoZheng109]

Suggest adding an in-repo regression test. This is a bugfix, but validation currently rests entirely on downstream pypto#2085 — simpler's own CI stays green because nothing in-repo passes prewarm_config into simpler_init (the scene-test framework always calls worker.init() without it). A future refactor of the TLS/prewarm path could silently reintroduce this null-runner segfault with simpler CI still green.

The repro is small (~20–40 lines, no golden/args boilerplate needed) since L2 trb prewarm runs synchronously inside cw.init:

• Build an L2 Worker(runtime="tensormap_and_ringbuffer", ...), call w.init(prewarm_config=CallConfig(<ring sizing>)), assert it succeeds. Pre-fix this segfaults on the null-runner deref; post-fix it returns cleanly.
• Must be on the trb runtime — host_build_graph links the weak no-op prewarm_config_impl and won't crash, so it can't catch the regression there. A pure a2a3sim test already covers the sim half of this fix and needs no device lock.
• prepared_callable/conftest.py already shows the fresh-L2-Worker construction pattern to copy.

If it can't land in this PR, worth filing an issue to track it.

[hashiqiqixian]

Added in 7f7082cf. The new tests/st/a2a3/tensormap_and_ringbuffer/test_prewarm_config.py constructs a fresh L2 TRB worker on a2a3sim, sets ring_task_window=64, and calls init(prewarm_config=config). This exercises the synchronous simpler_init prewarm path without device hardware or scene-test callable/golden boilerplate.

[hashiqiqixian]

CI is green except st-onboard-a5. That job failed during checkout before setup/tests because the self-hosted runner could not remove .pytest_cache/v/cache (EACCES: permission denied). All code-related jobs, including both a2a3sim scene-test jobs with the new regression test, passed. Could a maintainer please rerun the failed job? The PR author account does not have the repository admin permission required by GitHub to rerun it.