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fix(napi): disable mimalloc on Windows to fix worker_threads crash#18923

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fix/napi-windows-worker-threads
Feb 4, 2026
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fix(napi): disable mimalloc on Windows to fix worker_threads crash#18923
graphite-app[bot] merged 1 commit intomainfrom
fix/napi-windows-worker-threads

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@Boshen Boshen commented Feb 4, 2026

Summary

  • Disable mimalloc as the global allocator on Windows for all NAPI packages (oxc-parser, oxc-minify, oxc-transform)
  • On Windows, packages now use the system allocator instead

Fixes #15518

Root Cause

mimalloc has known issues with DLL unloading on Windows when the DLL is loaded by the main thread but unloaded by a worker thread (mimalloc issue #288). The cleanup code has _mi_is_main_thread() checks that prevent proper memory cleanup when called from a non-main thread, causing STATUS_ACCESS_VIOLATION crashes.

Platforms with mimalloc enabled

Platform mimalloc
macOS
Linux x86_64
Linux aarch64
Windows ❌ (disabled)
FreeBSD
ARM 32-bit
WASM

🤖 Generated with Claude Code

Copilot AI review requested due to automatic review settings February 4, 2026 06:36
@github-actions github-actions bot added A-parser Area - Parser A-minifier Area - Minifier A-transformer Area - Transformer / Transpiler C-bug Category - Bug labels Feb 4, 2026
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Pull request overview

This PR disables mimalloc as the global allocator on Windows for NAPI packages to fix worker_threads crashes caused by mimalloc's known DLL unloading issues on Windows. The fix addresses a critical bug where the main thread loads the DLL but a worker thread unloads it, triggering STATUS_ACCESS_VIOLATION crashes due to improper cleanup.

Changes:

  • Add target_os = "windows" to the exclusion list in conditional compilation for mimalloc in three NAPI packages
  • Update Cargo.toml dependency configurations to explicitly target only macOS instead of all non-Linux platforms

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

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File Description
napi/transform/src/lib.rs Adds Windows to the list of platforms excluded from using mimalloc as global allocator
napi/transform/Cargo.toml Changes mimalloc dependency from "not Linux/FreeBSD/ARM/WASM" to explicitly "macOS only"
napi/parser/src/lib.rs Adds Windows to the list of platforms excluded from using mimalloc as global allocator
napi/parser/Cargo.toml Changes mimalloc dependency from "not Linux/FreeBSD/ARM/WASM" to explicitly "macOS only"
napi/minify/src/lib.rs Adds Windows to the list of platforms excluded from using mimalloc as global allocator
napi/minify/Cargo.toml Changes mimalloc dependency from "not Linux/FreeBSD/ARM/WASM" to explicitly "macOS only"

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@Boshen Boshen added the 0-merge Merge with Graphite Merge Queue label Feb 4, 2026
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Boshen commented Feb 4, 2026

Merge activity

…18923)

## Summary

- Disable mimalloc as the global allocator on Windows for all NAPI packages (`oxc-parser`, `oxc-minify`, `oxc-transform`)
- On Windows, packages now use the system allocator instead

Fixes #15518

## Root Cause

mimalloc has known issues with DLL unloading on Windows when the DLL is loaded by the main thread but unloaded by a worker thread ([mimalloc issue #288](microsoft/mimalloc#288)). The cleanup code has `_mi_is_main_thread()` checks that prevent proper memory cleanup when called from a non-main thread, causing `STATUS_ACCESS_VIOLATION` crashes.

## Platforms with mimalloc enabled

| Platform | mimalloc |
|----------|----------|
| macOS | ✅ |
| Linux x86_64 | ✅ |
| Linux aarch64 | ✅ |
| Windows | ❌ (disabled) |
| FreeBSD | ❌ |
| ARM 32-bit | ❌ |
| WASM | ❌ |

🤖 Generated with [Claude Code](https://claude.ai/code)
@graphite-app graphite-app bot force-pushed the fix/napi-windows-worker-threads branch from a147751 to 487601b Compare February 4, 2026 07:44
@graphite-app graphite-app bot merged commit 487601b into main Feb 4, 2026
19 checks passed
@graphite-app graphite-app bot deleted the fix/napi-windows-worker-threads branch February 4, 2026 07:50
@graphite-app graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Feb 4, 2026
camc314 added a commit that referenced this pull request Feb 10, 2026
### 💥 BREAKING CHANGES

- 2bf7293 mangler: [**BREAKING**] Enable `top_level` by default for
modules and commonjs (#18278) (sapphi-red)
- 48b0542 span: [**BREAKING**] SourceType::ts should set module to
unambigious (#18873) (Boshen)

### 🚀 Features

- 500d071 minifier: Local traverse ctx and generated minifier traverse
(#19106) (Boshen)
- 142a1be parser: Detect binary files with TS1490 error (#19047)
(Boshen)
- e316857 allocator/bitset: Add `Ones` iterator to `BitSet` (#19027)
(sapphi-red)
- 742ad3f minifier: Default `invalid_import_side_effects` to `false`
(#18916) (sapphi-red)
- 0eff6be parser: Error JSX-like type assertions and generics in
`.mts`/`.cts` (#18910) (Boshen)
- 18320c6 span: Store file extension in `SourceType` (#18893) (Boshen)

### 🐛 Bug Fixes

- a7514e4 isolated-declarations: Preserve const context in literal type
inference (#19178) (camc314)
- 312e756 isolated-declarations: Preserve readonly literal initializers
(#19177) (camc314)
- d0ca8d0 isolated-declarations: Skip parenthesis when inferring type
(#19176) (camc314)
- 110c300 oxc_ecmascript: `+[false]` and `+[true]` should evaluate to
`NaN` (#19174) (copilot-swe-agent)
- f32ea19 semantic: Report redeclaration error for import bindings
conflicting with value declarations (#19068) (Boshen)
- 3aeba7a semantic: Report redeclaration error for `function a() {} var
a` in module mode (#19041) (Boshen)
- 35e32c6 coverage: Match Babel's options.json inheritance for test
fixtures (#19002) (Boshen)
- 463d60d semantic: Skip TS2391 for standalone computed-name class
methods (#19025) (Boshen)
- 56c086b parser: Add modifier ordering validation (TS1029) (#19024)
(Boshen)
- 6067a49 linter/jsdoc: False positive in `check-tag-names` for `@` in
email addresses and npm scopes (#19021) (Boshen)
- b13bb70 semantic/jsdoc: Inline tags like `{@link}` break jsdoc parsing
(#19019) (Boshen)
- e3609e3 regular_expression: Preserve UnicodeEscape CharacterKind in
string literals (#18998) (Boshen)
- 57917ee parser: Parse decorators on rest parameters (#18938) (Boshen)
- 487601b napi: Disable mimalloc on Windows to fix worker_threads crash
(#18923) (Boshen)
- 1f6b193 parser: Validate TypeScript import type options (#18889)
(Boshen)
- 1663184 parser: Allow conditional types in function type parameters
(#18886) (Boshen)
- 5758046 parser: Error on property access after instantiation
expression (#18887) (Boshen)
- 5eb4a94 parser: Handle `<<` as two `<` tokens in type argument
contexts (#18885) (Boshen)

### ⚡ Performance

- ed8c054 oxc_str: Add precomputed hash to Ident for fast HashMap
lookups (#19143) (Boshen)
- d4a0867 transformer_plugins: Switch ReplaceGlobalDefines from Traverse
to VisitMut (#19146) (Boshen)
- 9eb16b3 syntax: Pack ASCII identifier tables into single bitflag table
(#19088) (Boshen)
- e7595d1 mangler: Use BitSet for exported symbols set (#19023)
(sapphi-red)
- 2537924 semantic: Optimize scope resolution with fast paths and
inlining (#19029) (Boshen)
- 69a8d85 mangler: Use BitSet for keep_names symbols set (#19028)
(sapphi-red)
- f78c525 parser: Try hybrid parsing for jsx children and closing
element/fragments (#18789) (camchenry)

Co-authored-by: camc314 <18101008+camc314@users.noreply.github.com>
owjs3901 pushed a commit to owjs3901/oxc that referenced this pull request Feb 11, 2026
### 💥 BREAKING CHANGES

- 2bf7293 mangler: [**BREAKING**] Enable `top_level` by default for
modules and commonjs (oxc-project#18278) (sapphi-red)
- 48b0542 span: [**BREAKING**] SourceType::ts should set module to
unambigious (oxc-project#18873) (Boshen)

### 🚀 Features

- 500d071 minifier: Local traverse ctx and generated minifier traverse
(oxc-project#19106) (Boshen)
- 142a1be parser: Detect binary files with TS1490 error (oxc-project#19047)
(Boshen)
- e316857 allocator/bitset: Add `Ones` iterator to `BitSet` (oxc-project#19027)
(sapphi-red)
- 742ad3f minifier: Default `invalid_import_side_effects` to `false`
(oxc-project#18916) (sapphi-red)
- 0eff6be parser: Error JSX-like type assertions and generics in
`.mts`/`.cts` (oxc-project#18910) (Boshen)
- 18320c6 span: Store file extension in `SourceType` (oxc-project#18893) (Boshen)

### 🐛 Bug Fixes

- a7514e4 isolated-declarations: Preserve const context in literal type
inference (oxc-project#19178) (camc314)
- 312e756 isolated-declarations: Preserve readonly literal initializers
(oxc-project#19177) (camc314)
- d0ca8d0 isolated-declarations: Skip parenthesis when inferring type
(oxc-project#19176) (camc314)
- 110c300 oxc_ecmascript: `+[false]` and `+[true]` should evaluate to
`NaN` (oxc-project#19174) (copilot-swe-agent)
- f32ea19 semantic: Report redeclaration error for import bindings
conflicting with value declarations (oxc-project#19068) (Boshen)
- 3aeba7a semantic: Report redeclaration error for `function a() {} var
a` in module mode (oxc-project#19041) (Boshen)
- 35e32c6 coverage: Match Babel's options.json inheritance for test
fixtures (oxc-project#19002) (Boshen)
- 463d60d semantic: Skip TS2391 for standalone computed-name class
methods (oxc-project#19025) (Boshen)
- 56c086b parser: Add modifier ordering validation (TS1029) (oxc-project#19024)
(Boshen)
- 6067a49 linter/jsdoc: False positive in `check-tag-names` for `@` in
email addresses and npm scopes (oxc-project#19021) (Boshen)
- b13bb70 semantic/jsdoc: Inline tags like `{@link}` break jsdoc parsing
(oxc-project#19019) (Boshen)
- e3609e3 regular_expression: Preserve UnicodeEscape CharacterKind in
string literals (oxc-project#18998) (Boshen)
- 57917ee parser: Parse decorators on rest parameters (oxc-project#18938) (Boshen)
- 487601b napi: Disable mimalloc on Windows to fix worker_threads crash
(oxc-project#18923) (Boshen)
- 1f6b193 parser: Validate TypeScript import type options (oxc-project#18889)
(Boshen)
- 1663184 parser: Allow conditional types in function type parameters
(oxc-project#18886) (Boshen)
- 5758046 parser: Error on property access after instantiation
expression (oxc-project#18887) (Boshen)
- 5eb4a94 parser: Handle `<<` as two `<` tokens in type argument
contexts (oxc-project#18885) (Boshen)

### ⚡ Performance

- ed8c054 oxc_str: Add precomputed hash to Ident for fast HashMap
lookups (oxc-project#19143) (Boshen)
- d4a0867 transformer_plugins: Switch ReplaceGlobalDefines from Traverse
to VisitMut (oxc-project#19146) (Boshen)
- 9eb16b3 syntax: Pack ASCII identifier tables into single bitflag table
(oxc-project#19088) (Boshen)
- e7595d1 mangler: Use BitSet for exported symbols set (oxc-project#19023)
(sapphi-red)
- 2537924 semantic: Optimize scope resolution with fast paths and
inlining (oxc-project#19029) (Boshen)
- 69a8d85 mangler: Use BitSet for keep_names symbols set (oxc-project#19028)
(sapphi-red)
- f78c525 parser: Try hybrid parsing for jsx children and closing
element/fragments (oxc-project#18789) (camchenry)

Co-authored-by: camc314 <18101008+camc314@users.noreply.github.com>
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oxc-minify/oxc-transform cannot run on worker_threads in Windows

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