Function fork

crates/vm/src/stdlib/posix.rs:1002–1040

(vm: &VirtualMachine)

    #[pyfunction]
    fn fork(vm: &VirtualMachine) -> PyResult<i32> {
        if vm
            .state
            .finalizing
            .load(core::sync::atomic::Ordering::Acquire)
        {
            return Err(vm.new_exception_msg(
                vm.ctx.exceptions.python_finalization_error.to_owned(),
                "can't fork at interpreter shutdown".into(),
            ));
        }

        // RustPython does not yet have C-level audit hooks; call sys.audit()
        // to preserve Python-visible behavior and failure semantics.
        vm.sys_module
            .get_attr("audit", vm)?
            .call(("os.fork",), vm)?;

        py_os_before_fork(vm);

        let pid = unsafe { libc::fork() };
        // Save errno immediately — AfterFork callbacks may clobber it.
        let saved_errno = nix::Error::last_raw();
        if pid == 0 {
            py_os_after_fork_child(vm);
        } else {
            // Match CPython timing: capture this before parent after-fork hooks
            // in case those hooks start threads.
            let num_os_threads = get_number_of_os_threads();
            py_os_after_fork_parent(vm);
            // Match CPython timing: warn only after parent callback path resumes world.
            warn_if_multi_threaded("fork", num_os_threads, vm);
        }
        if pid == -1 {
            Err(nix::Error::from_raw(saved_errno).into_pyexception(vm))
        } else {
            Ok(pid)
        }
    }

    #[cfg(not(target_os = "redox"))]
    const MKNOD_DIR_FD: bool = cfg!(not(target_vendor = "apple"));