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#![allow(unsafe_code)]
use crate::backend::c;
use core::num::NonZeroI32;
/// A process identifier as a raw integer.
pub type RawPid = c::pid_t;
/// `pid_t`—A non-zero Unix process ID.
///
/// This is a pid, and not a pidfd. It is not a file descriptor, and the
/// process it refers to could disappear at any time and be replaced by
/// another, unrelated, process.
#[repr(transparent)]
#[derive(Copy, Clone, Eq, PartialEq, Debug, Hash)]
pub struct Pid(NonZeroI32);
impl Pid {
/// A `Pid` corresponding to the init process (pid 1).
pub const INIT: Self = Self(
// SAFETY: One is non-zero.
unsafe { NonZeroI32::new_unchecked(1) },
);
/// Converts a `RawPid` into a `Pid`.
///
/// Returns `Some` for strictly positive `RawPid`s. Otherwise, returns
/// `None`.
///
/// This is always safe because a `Pid` is a number without any guarantees
/// for the kernel. Non-child `Pid`s are always racy for any syscalls,
/// but can only cause logic errors. If you want race-free access or
/// control to non-child processes, please consider other mechanisms
/// like [pidfd] on Linux.
///
/// [pidfd]: https://man7.org/linux/man-pages/man2/pidfd_open.2.html
#[inline]
pub const fn from_raw(raw: RawPid) -> Option<Self> {
if raw > 0 {
// SAFETY: raw > 0.
unsafe { Some(Self::from_raw_unchecked(raw)) }
} else {
None
}
}
/// Converts a known strictly positive `RawPid` into a `Pid`.
///
/// # Safety
///
/// The caller must guarantee `raw` is strictly positive.
#[inline]
pub const unsafe fn from_raw_unchecked(raw: RawPid) -> Self {
debug_assert!(raw > 0);
Self(NonZeroI32::new_unchecked(raw))
}
/// Creates a `Pid` holding the ID of the given child process.
#[cfg(feature = "std")]
#[inline]
pub fn from_child(child: &std::process::Child) -> Self {
let id = child.id();
// SAFETY: We know the returned ID is valid because it came directly
// from an OS API.
unsafe { Self::from_raw_unchecked(id as i32) }
}
/// Converts a `Pid` into a `NonZeroI32`.
#[inline]
pub const fn as_raw_nonzero(self) -> NonZeroI32 {
self.0
}
/// Converts an `Option<Pid>` into a `RawPid`.
#[inline]
pub fn as_raw(pid: Option<Self>) -> RawPid {
pid.map_or(0, |pid| pid.0.get())
}
/// Test whether this pid represents the init process (pid 1).
#[inline]
pub const fn is_init(self) -> bool {
self.0.get() == Self::INIT.0.get()
}
}
#[test]
fn test_sizes() {
use core::mem::size_of;
assert_eq!(size_of::<RawPid>(), size_of::<NonZeroI32>());
assert_eq!(size_of::<RawPid>(), size_of::<Pid>());
}
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