Sandbox::https://github.com/RustPython/RustPython/pull/8728

youknowone · 2026-09-17T12:17:03Z

Summary

Implement os.wait3 and os.wait4 as wait4(2) with EINTR retry, matching the posix wait helper ((pid, status, resource.struct_rusage)).
wait3 is wait4(-1, ...). WNOHANG with no ready child returns a zeroed rusage.

This is the missing posix wait API that test_eintr skips via hasattr. It does not yet remove FLAKY_MP_TESTS; list(dict) already snapshots under one lock on main, and the remaining MP flakes (items-iteration race, test_thread_safety SIGSEGV skip, thread-start latency) need follow-up.

Test plan

test_wait3 and test_wait4 pass locally
CI snippets on macOS/Linux still pass

Summary by CodeRabbit

New Features
- Added POSIX wait3 and wait4 support for waiting on child processes.
- Process-wait results now include the child process ID, wait status, and resource usage details such as CPU time.
- Waiting operations can be interrupted and resumed when appropriate, while other system errors are reported.
- Non-blocking waits accurately indicate when no child process is ready.

Assisted-by: Grok:4.6

coderabbitai · 2026-09-17T12:17:27Z

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crates/host_env/src/posix.rs
crates/vm/src/stdlib/posix.rs

🚧 Files skipped from review as they are similar to previous changes (1)

crates/host_env/src/posix.rs

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📝 Walkthrough

Walkthrough

The POSIX host layer now provides wait3 and wait4 with resource usage. The VM layer exposes both functions to Python, converts RUsage to resource.struct_rusage, releases the VM thread during waits, and handles interruptions and errors.

Changes

POSIX wait support

Layer / File(s)	Summary
Host wait4 bindings `crates/host_env/src/posix.rs`	The host layer adds `wait3` and `wait4`. `wait3` waits for any child. A zero PID result returns zeroed resource usage. System-call errors propagate.
VM wait wrappers `crates/vm/src/stdlib/posix.rs`	The VM converts all 16 resource-usage fields to `resource.struct_rusage`, releases VM execution during waits, retries `EINTR` after signal checks, and exposes Python `wait3` and `wait4` functions.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Python as Python POSIX API
  participant VM as shared wait_with_rusage
  participant Host as host_env::posix
  participant Libc as libc wait4
  Python->>VM: Call wait3 or wait4
  VM->>Host: Wait with pid and options
  Host->>Libc: Call wait4
  Libc-->>Host: Return pid, status, and rusage
  Host-->>VM: Return pid, status, and RUsage
  VM-->>Python: Return pid, status, and resource.struct_rusage

Suggested reviewers: joshuamegnauth54

Merge Risk: ⚪ Minimal · up to 1af04

The added wait APIs are compatible with the supported target configurations examined, with no concrete merge-blocking risk identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 10 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding os.wait3 and os.wait4 with EINTR retry support.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
In `@crates/host_env/src/posix.rs`:
- Line 957: Update the wait4 FFI declaration to use NetBSD’s target-specific
__wait450 symbol, matching libc’s conditional link_name behavior, or reuse
libc::wait4 where supported. Preserve the existing wait4 call interface while
preventing the literal wait4 symbol from being linked on NetBSD.

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📒 Files selected for processing (2)

crates/host_env/src/posix.rs
crates/vm/src/stdlib/posix.rs

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Assisted-by: Grok:4.6

codspeed · 2026-09-17T16:00:54Z

Merging this PR will improve performance by 37.32%

⚡ 1 improved benchmark
✅ 65 untouched benchmarks

Performance Changes

	Benchmark	`BASE`	`HEAD`	Efficiency
⚡	`gc_collect.py[rustpython]`	910.6 ms	663.1 ms	+37.32%

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Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

_{Comparing youknowone:fix/flaky-mp (1af0497) with main (c382a60)}

Add os.wait3 and os.wait4 with EINTR retry

ba7503f

Assisted-by: Grok:4.6

Unskip multiprocessing Finalize thread-safety test

f2d4a63

Assisted-by: Grok:4.6

coderabbitai Bot reviewed Sep 17, 2026

View reviewed changes

Comment thread crates/host_env/src/posix.rs Outdated

Fix wait4 clippy lint and use libc wait4

1af0497

Assisted-by: Grok:4.6

youknowone merged commit 982cbd4 into RustPython:main Sep 18, 2026
31 checks passed

youknowone deleted the fix/flaky-mp branch September 18, 2026 02:03

youknowone mentioned this pull request Sep 18, 2026

Unskip MP tests and shrink the flaky MP CI list #8731

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Add os.wait3 and os.wait4 with EINTR retry - #8728

Add os.wait3 and os.wait4 with EINTR retry#8728
youknowone merged 3 commits into
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youknowone:fix/flaky-mp

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codspeed Bot commented Sep 17, 2026

Merging this PR will improve performance by 37.32%

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youknowone commented Sep 17, 2026 •

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