fix(sys): mimalloc3 v3.5.1 + fix for the process-init thread's thread-done hook by Brooooooklyn · Pull Request #97 · napi-rs/mimalloc-safe

Brooooooklyn · 2026-09-04T15:13:26Z

Background

mimalloc v3.5.0 (shipped in libmimalloc-sys2 0.1.61 / mimalloc-safe 0.1.65 by #92) never associates the process-init thread's theap with the pthread thread-done key. If the first thread that touches the allocator exits — a Node.js worker_threads worker that loads the addon first, then exits — _mi_thread_done never runs for it, its theap stays registered with its thread id, and the next thread that reuses that pthread TCB aborts in debug builds:

mimalloc: assertion failed: at "src/init.c":327, _mi_thread_init_with_heap
  assertion: "theap==NULL"

Release builds skip the assert but leak the dead thread's theap and pages. Linux only in practice (macOS enables MI_TLS_RECURSE_GUARD, which makes the new thread adopt the stale theap). Upstream culprit: microsoft/mimalloc@5d9cb381 ("remove static main theap and tld"); v3.4.5 was the last good tag. Reported upstream with the fix: microsoft/mimalloc#1393. Found via rolldown/rolldown#10268 CI (watch debounce timers survive a worker-first registrant that exited), which pinned mimalloc-safe = "=0.1.64" as a stopgap.

Changes

.gitmodules — mimalloc3 url microsoft/mimalloc → napi-rs/mimalloc, branch fix/first-thread-done (same approach as fix(sys): use THREAD_LOCAL TLS for mimalloc v3 on Apple #71).
mimalloc3 — 18b08671 (v3.5.0) → 1e5d14ca = upstream v3.5.1 + the 11-line src/init.c fix (associate the already-initialized default theap right after _mi_prim_thread_init_auto_done()). v3.5.1 additionally carries the upstream fix for realloc() on new thread incorrectly asserts on 3.5.0 on Linux microsoft/mimalloc#1371 (realloc assert on a new thread).
No change to build.rs, the v2 submodule, or the Rust sources.

Verification (Docker linux/arm64, node 22, debug + release builds of `example/` with `--features v3`)

tree	Node worker-first flow (1 / 64 / 64+4 concurrent workers)	Rust std threads reusing the dead TCB	release	`cargo test --features v3`	sys-test
v3.5.0 / v3.5.1 unfixed	assertion + SIGABRT	assertion + SIGABRT	OK (leaks)	—	—
`1e5d14ca`	OK	OK	OK	6/6	251/251

Bisect over v3.4.5..v3.5.0 (7 steps) isolates 5d9cb381. The v2 line (c_src/mimalloc v2.5.0) does not have the gap and passes the same flow.

Once released, rolldown can drop its =0.1.64 pin.

🤖 Generated with Claude Code

https://claude.ai/code/session_01T34fMrYCf2V13Mg8BKmnda

Note

High Risk
Touches process-wide allocator and per-thread teardown in native code; wrong behavior can cause crashes or leaks in multi-threaded hosts (e.g. Node worker_threads), though scope is limited to the v3 submodule.

Overview
Repoints the mimalloc3 git submodule from microsoft/mimalloc (dev3) to napi-rs/mimalloc on branch fix/first-thread-done, matching the prior fork-based workflow used for targeted allocator fixes.

That branch carries mimalloc v3.5.1 plus a small src/init.c change so the process-init thread’s default heap is registered with the pthread thread-done hook. Without it, a worker thread that is the first allocator user and then exits can leave a stale heap on reused pthread TCBs (debug abort in _mi_thread_init_with_heap, leaks in release on Linux).

No Rust build.rs or crate source changes in this diff; consumers get the fix via the updated vendored mimalloc3 tree.

^{Reviewed by Cursor Bugbot for commit dd53da2. Bugbot is set up for automated code reviews on this repo. Configure here.}

…-done hook mimalloc v3.5.0 (shipped by #92) never associates the process-init thread's theap with the pthread thread-done key. When the first thread that touches the allocator exits (a Node.js worker that loads the addon first), `_mi_thread_done` never runs for it, its theap stays registered with its thread id, and the next thread that reuses that pthread TCB aborts in debug builds: mimalloc: assertion failed: at "src/init.c":327, _mi_thread_init_with_heap assertion: "theap==NULL" Release builds skip the assert but leak the dead thread's theap and pages. Upstream culprit: microsoft/mimalloc@5d9cb381; reported with the fix as microsoft/mimalloc#1393. Point the `mimalloc3` submodule at the napi-rs/mimalloc fork branch `fix/first-thread-done` = upstream v3.5.1 + the 11-line src/init.c fix (same approach as #71), until upstream ships it. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01T34fMrYCf2V13Mg8BKmnda

cursor · 2026-09-04T15:13:34Z

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chatgpt-codex-connector · 2026-09-04T15:13:41Z

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📝 Code Review	✅ Completed 2026-09-04T15:15:48.078684Z	`dd53da2`	PR opened

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## 🤖 New release * `libmimalloc-sys2`: 0.1.61 -> 0.1.62 (✓ API compatible changes) * `mimalloc-safe`: 0.1.65 -> 0.1.66 (✓ API compatible changes) <details><summary>Changelog</summary> ## `libmimalloc-sys2` <blockquote> ## [0.1.62] - 2026-09-04 ### Bug Fixes - *(sys)* Mimalloc3 v3.5.1 + fix for the process-init thread's thread-done hook ([#97](#97)) ### Chore - *(deps)* Update mimalloc (v2) submodule to v2.5.1 ([#98](#98)) </blockquote> ## `mimalloc-safe` <blockquote> ## [0.1.66] - 2026-09-04 ### Bug Fixes - *(sys)* Mimalloc3 v3.5.1 + fix for the process-init thread's thread-done hook ([#97](#97)) ### Chore - *(deps)* Update dependency @napi-rs/cli to v3.9.0 ([#94](#94)) - *(deps)* Update dependency @emnapi/core to v2.0.0-alpha.5 ([#95](#95)) - *(deps)* Update dependency @emnapi/runtime to v2.0.0-alpha.5 ([#96](#96)) - *(deps)* Update mimalloc (v2) submodule to v2.5.1 ([#98](#98)) </blockquote> </details> --- This PR was generated with [release-plz](https://github.com/release-plz/release-plz/). Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

## 🤖 New release * `libmimalloc-sys2`: 0.1.61 -> 0.1.62 * `mimalloc-safe`: 0.1.65 -> 0.1.66 <details><summary>Changelog</summary> ## `libmimalloc-sys2` <blockquote> ## [0.1.62] - 2026-09-04 ### Bug Fixes - *(sys)* Mimalloc3 v3.5.1 + fix for the process-init thread's thread-done hook ([#97](#97)) ### Chore - *(deps)* Update mimalloc (v2) submodule to v2.5.1 ([#98](#98)) </blockquote> ## `mimalloc-safe` <blockquote> ## [0.1.66] - 2026-09-04 ### Bug Fixes - *(sys)* Mimalloc3 v3.5.1 + fix for the process-init thread's thread-done hook ([#97](#97)) ### Chore - *(deps)* Update dependency @napi-rs/cli to v3.9.0 ([#94](#94)) - *(deps)* Update dependency @emnapi/core to v2.0.0-alpha.5 ([#95](#95)) - *(deps)* Update dependency @emnapi/runtime to v2.0.0-alpha.5 ([#96](#96)) - *(deps)* Update mimalloc (v2) submodule to v2.5.1 ([#98](#98)) </blockquote> </details> --- This PR was generated with [release-plz](https://github.com/release-plz/release-plz/). Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

0.1.66 ships mimalloc v3.5.1 plus the fix for the process-init thread's thread-done hook (see microsoft/mimalloc#1393, napi-rs/mimalloc-safe#97), so the `=0.1.64` stopgap from 4855394 is no longer needed. Cargo.lock: mimalloc-safe 0.1.64 -> 0.1.66, libmimalloc-sys2 0.1.60 -> 0.1.62. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01T34fMrYCf2V13Mg8BKmnda

… fix (#104) ### Background Upstream closed microsoft/mimalloc#1393 and took the fix in a different form: microsoft/mimalloc@439dc27b, shipped in **v3.5.2**. That commit works on the default TLS model (verified with the #1393 repro on Linux, debug shared build: `e35400bd` aborts, `v3.5.2` prints `OK`). But it moved `mi_process_setup_auto_thread_done()` into `mi_process_init_once()` **before** `_mi_process_is_initialized = true`. With `MI_TLS_RECURSE_GUARD` (auto-on for `MI_TLS_MODEL_LOCAL` on Apple, which is what `build.rs` forces for v3 on macOS) `_mi_theap_default()` returns `_mi_theap_empty` at that point: ``` mi_process_init_once() [v3.5.2 src/init.c:558-564] ├─ mi_thread_init() __mi_theap_default = &mi_process_theap_main ├─ _mi_tls_slots_init() ├─ _mi_thread_locals_init() ├─ mi_process_setup_auto_thread_done() │ └─ _mi_theap_default() ──► RECURSE_GUARD: _mi_process_is_initialized == false │ ──► returns &_mi_theap_empty │ ──► debug: assert fires / release: no association └─ _mi_process_is_initialized = true ← too late ``` So on plain `v3.5.2`, `cargo test --features v3` on macOS aborts at process init in every debug binary: ``` mimalloc: assertion failed: at "src/init.c":450, mi_process_setup_auto_thread_done assertion: "mi_theap_is_initialized(theap)" ``` and release builds silently skip the association, i.e. the #1393 leak is back on macOS. Reproducible with upstream alone: `cmake -DCMAKE_BUILD_TYPE=Debug -DMI_TLS_MODEL=LOCAL` on macOS, `./mimalloc-test-api` passes on v3.5.1 and aborts on v3.5.2. Same on Linux with `-DMI_TLS_RECURSE_GUARD=ON`. ### Changes - **`mimalloc`** (v2) — `v2.5.1` → `v2.5.2` (official tag, no patches). - **`mimalloc3`** — napi-rs fork `1e5d14ca` (v3.5.1 + #1393) → napi-rs fork `afa6c90d` = upstream **v3.5.2** + one-line fix: set `_mi_process_is_initialized = true` before `mi_process_setup_auto_thread_done()` (napi-rs/mimalloc@afa6c90d, branch `fix/process-init-flag-before-thread-done`). Same approach as #71 / #97. - **`.gitmodules`** — `mimalloc3` branch name updated. - No change to `build.rs` or the Rust sources. ### Verification Upstream, macOS arm64, Debug, `-DMI_TLS_MODEL=LOCAL`: | tree | `mimalloc-test-api` | |---|---| | v3.5.1 | 50/50 | | v3.5.2 | abort at process init (134) | | v3.5.2 + `afa6c90d` | 50/50 | Upstream, Linux x64 (Docker gcc:14), Debug shared, #1393 repro: | tree | `RECURSE_GUARD=OFF` | `RECURSE_GUARD=ON` | |---|---|---| | v3.5.2 | OK | abort (134) | | v3.5.2 + `afa6c90d` | OK | OK | This repo, macOS arm64, every CI command: `cargo test` / `--features secure` / `extended` / `v3` / `extended,v3` all pass; `libmimalloc-sys-test` 258/258 (v2, secure, extended) and 251/251 (v3). Pre-existing and untouched: upstream `mimalloc-test-stress-heaps` fails the `refcount == 1` assert with `MI_TLS_MODEL=LOCAL` on macOS on v3.5.1 too; `extended::tests::runtime_stable_option` fails under `cargo test --workspace` on v2.5.1 too (not in CI). 🤖 Generated with [Claude Code](https://claude.com/claude-code) https://claude.ai/code/session_016srh5svTkqfW21zGcU6ht9  --- > [!NOTE] > **Medium Risk** > Changes which mimalloc v3 C sources are built, affecting process/thread allocator initialization on macOS and other TLS recurse-guard configurations. > > **Overview** > Points the **`mimalloc3`** git submodule at the napi-rs fork branch **`fix/process-init-flag-before-thread-done`** instead of **`fix/first-thread-done`**, so v3 tracks upstream **v3.5.2** plus a one-line init ordering fix: set `_mi_process_is_initialized` before `mi_process_setup_auto_thread_done()`. > > That avoids macOS **`MI_TLS_MODEL_LOCAL`** / recurse-guard failures where v3.5.2 alone aborts in debug or reintroduces the #1393 leak in release. No Rust or `build.rs` changes in this diff—only the submodule branch pin in **`.gitmodules`**. > > Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit 09fc0c6. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).  Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Brooooooklyn merged commit 6aba2ab into main Sep 4, 2026
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Brooooooklyn deleted the fix/mimalloc3-first-thread-done branch September 4, 2026 15:21

github-actions Bot mentioned this pull request Aug 24, 2026

chore: release #93

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Brooooooklyn mentioned this pull request Sep 4, 2026

chore(deps): update mimalloc (v2) submodule to v2.5.1 #98

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github-actions Bot mentioned this pull request Sep 4, 2026

chore: release #99

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pheuter mentioned this pull request Sep 10, 2026

SIGBUS/SIGSEGV at native teardown during vite build on Linux x64 — starts with rolldown 1.2.8 rolldown/rolldown#10860

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Brooooooklyn mentioned this pull request Sep 14, 2026

chore(deps): update mimalloc to v2.5.2 and mimalloc3 to v3.5.2 + init fix #104

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fix(sys): mimalloc3 v3.5.1 + fix for the process-init thread's thread-done hook - #97

fix(sys): mimalloc3 v3.5.1 + fix for the process-init thread's thread-done hook#97
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