1 | //! The `Pid` type. |
2 | |
3 | #![allow (unsafe_code)] |
4 | |
5 | use crate::backend::c; |
6 | use core::num::NonZeroI32; |
7 | |
8 | /// A process identifier as a raw integer. |
9 | pub type RawPid = c::pid_t; |
10 | |
11 | /// `pid_t`—A non-zero Unix process ID. |
12 | /// |
13 | /// This is a pid, and not a pidfd. It is not a file descriptor, and the |
14 | /// process it refers to could disappear at any time and be replaced by |
15 | /// another, unrelated, process. |
16 | #[repr (transparent)] |
17 | #[derive (Copy, Clone, Eq, PartialEq, Debug, Hash)] |
18 | pub struct Pid(NonZeroI32); |
19 | |
20 | impl Pid { |
21 | /// A `Pid` corresponding to the init process (pid 1). |
22 | pub const INIT: Self = Self(match NonZeroI32::new(1) { |
23 | Some(n) => n, |
24 | None => panic!("unreachable" ), |
25 | }); |
26 | |
27 | /// Converts a `RawPid` into a `Pid`. |
28 | /// |
29 | /// Returns `Some` for positive `RawPid`s. Otherwise, returns `None`. |
30 | /// |
31 | /// This is safe because a `Pid` is a number without any guarantees for the |
32 | /// kernel. Non-child `Pid`s are always racy for any syscalls, but can only |
33 | /// cause logic errors. If you want race-free access to or control of |
34 | /// non-child processes, please consider other mechanisms like [pidfd] on |
35 | /// Linux. |
36 | /// |
37 | /// [pidfd]: https://man7.org/linux/man-pages/man2/pidfd_open.2.html |
38 | #[inline ] |
39 | pub const fn from_raw(raw: RawPid) -> Option<Self> { |
40 | if raw > 0 { |
41 | // SAFETY: We just checked that `raw > 0`. |
42 | unsafe { Some(Self::from_raw_unchecked(raw)) } |
43 | } else { |
44 | None |
45 | } |
46 | } |
47 | |
48 | /// Converts a known positive `RawPid` into a `Pid`. |
49 | /// |
50 | /// # Safety |
51 | /// |
52 | /// The caller must guarantee `raw` is positive. |
53 | #[inline ] |
54 | pub const unsafe fn from_raw_unchecked(raw: RawPid) -> Self { |
55 | debug_assert!(raw > 0); |
56 | Self(NonZeroI32::new_unchecked(raw)) |
57 | } |
58 | |
59 | /// Creates a `Pid` holding the ID of the given child process. |
60 | #[cfg (feature = "std" )] |
61 | #[inline ] |
62 | pub fn from_child(child: &std::process::Child) -> Self { |
63 | let id = child.id(); |
64 | // SAFETY: We know the returned ID is valid because it came directly |
65 | // from an OS API. |
66 | unsafe { Self::from_raw_unchecked(id as i32) } |
67 | } |
68 | |
69 | /// Converts a `Pid` into a `NonZeroI32`. |
70 | #[inline ] |
71 | pub const fn as_raw_nonzero(self) -> NonZeroI32 { |
72 | self.0 |
73 | } |
74 | |
75 | /// Converts an `Option<Pid>` into a `RawPid`. |
76 | #[inline ] |
77 | pub fn as_raw(pid: Option<Self>) -> RawPid { |
78 | pid.map_or(0, |pid| pid.0.get()) |
79 | } |
80 | |
81 | /// Test whether this pid represents the init process (pid 1). |
82 | #[inline ] |
83 | pub const fn is_init(self) -> bool { |
84 | self.0.get() == Self::INIT.0.get() |
85 | } |
86 | } |
87 | |
88 | #[test ] |
89 | fn test_sizes() { |
90 | use core::mem::transmute; |
91 | |
92 | assert_eq_size!(RawPid, NonZeroI32); |
93 | assert_eq_size!(RawPid, Pid); |
94 | assert_eq_size!(RawPid, Option<Pid>); |
95 | |
96 | // Rustix doesn't depend on `Option<Pid>` matching the ABI of a raw integer |
97 | // for correctness, but it should work nonetheless. |
98 | const_assert_eq!(0 as RawPid, unsafe { |
99 | transmute::<Option<Pid>, RawPid>(None) |
100 | }); |
101 | const_assert_eq!(4567 as RawPid, unsafe { |
102 | transmute::<Option<Pid>, RawPid>(Some(Pid::from_raw_unchecked(4567))) |
103 | }); |
104 | } |
105 | |