[shinaoka]

Returns main to the Rayon version and prepares threadteam 0.2.0.

Maintainer decision (2026-10-30): 「0.3.0でいいよ．あと，独自スレッド版はdevelop branchに保存しよう．しばらくはRayon版を出版し続けて，Rayonで何ができないか熟考してから判断する．」

The own-threads version (#16, plus the 0.2.0 version bump of #17) is kept on develop (= 302c37d). If it ships, it ships as 0.3.0.

Closes #20. Supersedes #19, which is closed after this merges.

What changes

• src/, tests/, docs/, scripts/, benches/ are as on [experiment, do not merge] Reuse the private Rayon pool between pools of one width (faer#107 comparison) #19's 9dfcbdb:

  • Rayon underneath, with libgomp's waits;
  • the per-width cache of the private Rayon pool;
  • bench-ab.sh with the HEAD2 side.

  Ordinary commit on main, no force-push. git diff 9dfcbdb HEAD touches only Cargo.toml, Cargo.lock, README.md and docs/design/placement.md.

• Removed from main (kept on develop):

  • docs/design/own-threads.md;
  • src/worker.rs;
  • tests/own_threads.rs;
  • the rayon opt-in feature and Exec::external_rayon. These were never published.

• Version 0.2.0. There are no breaking signatures. cargo public-api diff v0.1.3..HEAD shows additions only:

  • PoolBuilder::spin_polls;
  • Pool::spin_polls.

  The bump is minor because of a contract change: dropping a pool with the default thread settings no longer joins its threads, it caches them.

• README.

  • A short paragraph on the Rayon pool reuse.
  • The shutdown contract now distinguishes dedicated and default pools.
  • "Upgrading from 0.1" is rewritten for this version:
    • spin_polls is added;
    • the waits follow libgomp;
    • a default pool's drop caches its Rayon pool, and a pool of the same width reuses it, re-applying the caller's CPU set;
    • idle_runs_rayon, external and the parallel → Rayon dependency are unchanged.

• docs/design/placement.md.

  • The drop paragraph covers the cache.
  • The decision record above, with the link to develop.

• There is no CHANGELOG in this repository.

Verification (primerose, on 7ee9287)

The pre-push checklist of AGENTS.md, plus more:

• fmt;
• clippy with all features and with no default features (-D warnings);
• cargo test with default features, all features (twice) and no default features;
• loom: RUSTFLAGS="--cfg loom", 7 models;
• cargo deny check bans;
• scripts/check-no-public-rayon.sh;
• cargo doc with and without all features;
• cargo check --target aarch64-apple-darwin;
• taskset -c 0-2, three times: idle_clock, oversubscribed, team, rayon_reuse, team_owner, alloc_free and drop_join;
• cargo package: 111 files, 238 KB, with the same metadata as 0.1.3.

The CI of #19 on the same sources is green (macOS and Ubuntu tests, loom, clippy, doc, placement rules, rustfmt).

After merge (maintainer-approved)

• cargo publish 0.2.0 from the merge commit;
• tag v0.2.0;
• close [experiment, do not merge] Reuse the private Rayon pool between pools of one width (faer#107 comparison) #19.

The monitor merges.

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