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@sdogruyol sdogruyol released this 29 Jul 16:01
· 268 commits to master since this release
v0.15.0
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Learn about vigilant mode.

Correctness release: process-STW × TLAB freelist UAF class fixed and CI-gated;
process-STW MT property harness; acikturkiye Linux re-cut measured; shard RSS
dead-end defaults documented. Supported path remains EC parallelism 1,
GCRY_TLAB off (Parallel+TLAB stays experimental).

Performance

  • Linux Kemal (same-host median-of-3, wrk -c 100 -d 30, scrub on): /json ~86% of Boehm @ ~0.77× post-GC RSS; / ~86% @ ~0.76×. Session bench/log/linux/2026-07-29-151144/ (bebedae). Collector defaults unchanged vs 0.14 — thr within host noise of the v0.14 ~89% cut. See docs/PERF.md (Linux).
  • acikturkiye Linux re-cut (measured): /api/v1/ ~90% of Boehm thr @ ~2.54× post-GC RSS (median-of-3, wrk -c 100 -d 30, scrub on). Session bench/log/linux/2026-07-29-112202/ (9decd01). Replaces the v0.14.0 ~93% / ~2.65× estimate. See docs/ACIKTURKIYE.md.
  • Shard RSS A/B (defaults unchanged): same-host cuts rejected as defaults — Linux HOLED GCRY_PAGE_DONTNEED, process-default curated HTTP::Headers::Key Hash layout, collect-time mutator clear_stack, Linux 1 MiB large-cache floor. Keep fiber scrub, Linux 4 MiB large-cache, HOLED opt-in; Headers layout stays app-side / GCRY_AUTO_LAYOUTS. See docs/ACIKTURKIYE.md “Don’t bother”.

Fixed

  • Explicit-root list × process STW race: add_root/delete_root could run concurrently with stop_world, freezing a mutator mid-list splice so @roots.each walked a freed/next-corrupt RootNode (SEGV at run_collection during stw_mt_property_test). Serialize mutations with @roots_lock acquired before STW; collector may mutate without the lock while @world_stopped.
  • Parked-fiber scrub on thinly mapped stacks: Cap wipe to the same 512 B fiber path as clear_stack and zero only readable pages via Roots.clear_range_safe (defense in depth; Crystal fiber stacks grow on demand).
  • TLAB + Parallel under process STW: mid-tlab_alloc_small STW could leave FREE freelist nodes only reachable from mutator stacks; mark ignored FREE, then empty-chunk release munmapped them (and unlink_freelist_range could coerce USED→FREE). Fix: claim FREE stack/thread roots when TLAB+STW (clear FREE but keep next_free so scrub can walk the chain — set_used was severing freelists → OOM), freelist scrub after flush/mark (TLAB-only), flush only FREE nodes, TLAB epoch + detach-before-claim (no dual-alloc after flush), no nested collect under @alloc_lock (deadlock), unlock-and-collect retry on refill miss, steal stranded TLAB freelists, skip nil Thread#current_fiber under Parallel. CI gates stw_mt_property_test --tlab --workers=2,4.

Added

  • Process-GC STW MT property harness: bench/stw_mt_property_test.cr (-Dgc_none) runs Parallel allocator workers while the default EC pins roots (ACK handshake) and GC.collects under real STW. Closes the gap left by library-heap mt_property_test (stop_the_world=false). CI gates --workers=2,4 and --tlab --workers=2,4. (make stw-mt-property-test)

Changed

  • Docs / knobs: Linux HOLED page release documented as opt-in (post-STW; not “STW-heavy”). Large-cache defaults clarified (Linux process 4 MiB, Darwin 1 MiB). Darwin GCRY_DISABLE_PAGE_RELEASE=1 / GCRY_DISABLE_MADVISE=1 explicitly clear madvise_free_pages.
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