clear_after_fork by youknowone · Pull Request #6933 · RustPython/RustPython

youknowone

📝 Walkthrough

Walkthrough

Adds post-fork cleanup routines for signal state, wakeup file descriptors, and weakref locks. These functions reset inherited parent state in child processes before Python code execution, preventing stale parent signals and locks from interfering with child process behavior.

Changes

Cohort / File(s)	Summary
Signal state cleanup `crates/vm/src/signal.rs`, `crates/vm/src/stdlib/signal.rs`	Added UNIX-only functions to reset global signal state (`clear_after_fork()`) and wakeup fd state (`clear_wakeup_fd_after_fork()`) after fork operations.
Weakref lock cleanup `crates/vm/src/object/core.rs`	Added UNIX-only functions to reset weakref stripe locks (`reset_all_after_fork()`) and a public wrapper (`reset_weakref_locks_after_fork()`) guarded by threading configuration.
Post-fork orchestration `crates/vm/src/stdlib/posix.rs`	Integrated cleanup calls into `py_os_after_fork_child()` to invoke signal, wakeup fd, and weakref lock resets before Python code runs in child process.

Sequence Diagram

sequenceDiagram
    participant Fork Process
    participant Child Init as py_os_after_fork_child()
    participant Signal Module
    participant Signal FD Module
    participant Weakref Module

    Fork Process->>Child Init: fork() → child process starts
    Child Init->>Signal Module: clear_after_fork()
    Signal Module->>Signal Module: reset ANY_TRIGGERED & TRIGGERS
    Signal Module-->>Child Init: ✓ signal state cleared
    Child Init->>Signal FD Module: clear_wakeup_fd_after_fork()
    Signal FD Module->>Signal FD Module: reset WAKEUP to INVALID_WAKEUP
    Signal FD Module-->>Child Init: ✓ wakeup fd cleared
    Child Init->>Weakref Module: reset_weakref_locks_after_fork()
    Weakref Module->>Weakref Module: reset all stripe locks
    Weakref Module-->>Child Init: ✓ weakref locks cleared
    Child Init->>Child Init: run after_fork_child(vm)
    Child Init-->>Fork Process: child initialized & ready

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

impl preexec_fn #6479: Modifies child-after-fork execution path and VM handling during fork operations.
various fix to support subprocess/multiprocessing #6567: Adds RLock recursion reset to child-after-fork reinitialization, complementing this PR's other state resets.

Poem

🐰 A fork in the road, the process did split,
Locks and signals left in a bit of a fit!
Reset, reset, the rabbit did say,
Clear state before Python runs its way! 🔄

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'clear_after_fork' directly matches the primary objective of the changes: adding fork-safe cleanup functions to reset global state (signals, weakref locks, wakeup FDs) after process forking.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing touches

📝 Generate docstrings

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment

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