fix: bump mimalloc to 0.1.51 to fix win-arm64 process-exit crash#6176
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ruben-arts merged 2 commits intoMay 21, 2026
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mimalloc 0.1.50 / libmimalloc-sys 0.1.47 (resolved in pixi 0.69.0) bundle mimalloc C v3.3.1, which crashes at process exit on Windows ARM64 with STATUS_ACCESS_VIOLATION (0xC0000005). Root cause: the MSVC C atomic wrapper on ARM64 used compare-exchange (a write-capable instruction) to implement loads of read-only sentinel objects, which triggers an access violation on read-only pages. Upstream fix: microsoft/mimalloc@60a1f3b, shipped in mimalloc v3.3.2, vendored into libmimalloc-sys 0.1.48 / mimalloc 0.1.51. Refs: microsoft/mimalloc#1277, astral-sh/uv#19192.
Prevent regressions to the buggy mimalloc 0.1.49 / 0.1.50 wrappers (which bundle the broken mimalloc C v3.3.0 / v3.3.1) by raising the minimum version requirement. The Cargo.lock already pins 0.1.51.
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Description
Any pixi command exits with
STATUS_ACCESS_VIOLATION(0xC0000005, decimal3221225477) on win-arm64 in 0.69.0. The crash happens after pixi has finished its work and printed all output, in a process-exit destructor, not in pixi logic. setup-pixi surfaces it because the runner treats the non-zero exit as a failure:Root cause. The crash is in mimalloc, our global allocator on Windows (
crates/pixi_allocator/src/lib.rs). Between 0.68.1 and 0.69.0, uv bumps transitively raised the resolved versions:mimalloc: 0.1.48 -> 0.1.50libmimalloc-sys: 0.1.44 -> 0.1.47That bump silently flipped the bundled C library from mimalloc v2 to mimalloc v3.3.1. The wrapper's opt-in feature flag was renamed from
v3tov2in 0.1.49, inverting the default; pixi pins no features, so we tracked whatever the new default was.mimalloc v3.3.0 / v3.3.1 has a known win-arm64 bug (microsoft/mimalloc#1277): the MSVC C atomic wrapper on ARM64 uses compare-exchange (a write-capable instruction) to implement loads of read-only sentinel objects, which triggers an access violation on read-only pages. The symptom in the linked issue matches byte-for-byte:
exit code: 0xc0000005, STATUS_ACCESS_VIOLATION. uv and ruff hit the same bug (astral-sh/uv#19192, astral-sh/ruff#24880); they pinned tomimalloc/v2before v3.3.2 shipped.Fix. Upstream fixed it in microsoft/mimalloc@60a1f3b, shipped in mimalloc C v3.3.2 (verified
git compare v3.3.2...60a1f3bshows v3.3.2 contains the commit). That vendored C version landed inlibmimalloc-sys 0.1.48/mimalloc 0.1.51. This PR:libmimalloc-sys 0.1.47 -> 0.1.48andmimalloc 0.1.50 -> 0.1.51inCargo.lock.crates/pixi_allocator/Cargo.tomlto0.1.51so future resolutions can't drop back to a buggy version.No source code changes.
How Has This Been Tested?
pixi info --manifest-path ...); should exit 0 with this branch where 0.69.0 exits 3221225477.AI Disclosure
Tools: Claude Code
Checklist: