macOS: bundled oils shell intermittently fails fast external commands (getpgid ESRCH race)
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Assessment
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Newbie friendliness
- 68/100
- Issue type
- Bug
- Clarity
- Clearly specified
- Activity status
- Active
- Domain
- build-system, testing-qa
Research direction
Read crates/fspy/build.rs and locate MACOS_BINARY_DOWNLOADS; first confirm an Oils release containing upstream PR #2689, then rebuild the bundled macOS binary. Run the parallel fast-command reproduction and smoke script, checking for no failures and byte-identical smoke output.
Written by the indexing model from the issue text.
Description
Symptom
A cached task on macOS intermittently reports exit 2 with empty stdout and oils I/O error (main): No such process on stderr. Seen in the wild running parallel test suites that spawn vp run (each task runs under the bundled osh, which fspy substitutes for /bin/sh).
Root cause
Not fspy's exec interposition — the bundled oils 0.37.0 itself. Process::RunProcess (core/process.py) calls getpgid(child_pid) right after fork() and before waitpid(). On macOS, getpgid() of a zombie child fails with ESRCH, so when the parent is descheduled past a fast command's exit (CPU contention), the OSError escapes to oils' main() → exit 2.
Reproduces with the raw oils binary, no fspy involved: ~5% under 6-8-way parallel loops of osh -c 'echo x > f; cat f'.
Fix
Upstream PR: https://github.com/oils-for-unix/oils/pull/2689 — gate the getpgid() on job control being enabled (MaybeGiveTerminal() no-ops otherwise, so batch shells never needed the pgid).
Once an oils release includes it: rebuild the bundled binary and bump MACOS_BINARY_DOWNLOADS in crates/fspy/build.rs.
Verification of the fix
Patched 0.37.0 tarball build (same one-liner in the generated C++): 2000 concurrent runs of the failing shapes, 0 failures (vs ~5% before); smoke script output byte-identical to the unpatched binary.
- Dominant language
- Rust
- Stars
- 466
- Forks
- 42
- Avg merge
- 1d 20h
- Merged PRs (30d)
- 21
Contributor guide
First steps
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