rigtop_core/linux/
procstat.rs

1//! Thread counts from `/proc/<pid>/stat`.
2//!
3//! `sysinfo` only knows a process's threads when it refreshes every thread
4//! as well (`/proc/<pid>/task/*`), which costs several reads per thread on
5//! every sample: on a desktop with thousands of browser and Electron
6//! threads, that is most of the collection time. The count itself is one
7//! field of the process's own `stat` file.
8
9use std::fs;
10
11use super::SysRoots;
12
13/// Number of threads of `pid`, or `None` if it is gone or unreadable.
14pub fn thread_count(roots: &SysRoots, pid: u32) -> Option<u32> {
15    read(roots, pid)?.threads
16}
17
18/// What is read from a process's `stat` line.
19#[derive(Debug, Clone, Copy, PartialEq, Eq)]
20pub struct ProcStat {
21    pub threads: Option<u32>,
22    pub nice: Option<i32>,
23}
24
25/// The thread count and nice value of `pid`, from one read of its `stat`.
26pub fn read(roots: &SysRoots, pid: u32) -> Option<ProcStat> {
27    let text = fs::read_to_string(roots.proc.join(pid.to_string()).join("stat")).ok()?;
28    Some(ProcStat {
29        threads: parse_thread_count(&text),
30        nice: parse_nice(&text),
31    })
32}
33
34/// Field 19 (`nice`) of a `stat` line, counted like [`parse_thread_count`].
35pub(crate) fn parse_nice(stat: &str) -> Option<i32> {
36    let after_name = &stat[stat.rfind(')')? + 1..];
37    after_name.split_whitespace().nth(16)?.parse().ok()
38}
39
40/// Field 20 (`num_threads`) of a `stat` line. The command name (field 2) is
41/// in parentheses and may itself contain spaces and parentheses, so fields
42/// are counted from the last `)`.
43pub(crate) fn parse_thread_count(stat: &str) -> Option<u32> {
44    let after_name = &stat[stat.rfind(')')? + 1..];
45    // Field 3 (state) is the first one after the name, so field 20 is the 18th.
46    after_name.split_whitespace().nth(17)?.parse().ok()
47}
48
49#[cfg(test)]
50mod tests {
51    use super::*;
52    use crate::linux::testutil::write;
53
54    #[test]
55    fn counts_threads_even_with_odd_command_names() {
56        let stat = "4242 (Web Content (x)) S 1 4242 4242 0 -1 4194560 100 0 0 0 \
57                    50 20 0 0 20 0 37 0 1234 567890 1000 18446744073709551615";
58        assert_eq!(parse_thread_count(stat), Some(37));
59        assert_eq!(parse_nice(stat), Some(0));
60        let niced = "77 (make) R 1 77 77 0 -1 4194560 100 0 0 0 50 20 0 0 30 10 1 0";
61        assert_eq!(parse_nice(niced), Some(10));
62        assert_eq!(parse_thread_count("1 (init) S 1"), None, "truncated");
63        assert_eq!(parse_thread_count("garbage"), None);
64    }
65
66    #[test]
67    fn reads_from_proc() {
68        let tmp = tempfile::tempdir().unwrap();
69        write(
70            tmp.path(),
71            "proc/7/stat",
72            "7 (rigtop) R 1 7 7 0 -1 0 0 0 0 0 0 0 0 0 20 0 3 0 1 1 1\n",
73        );
74        let roots = SysRoots {
75            sys: tmp.path().join("sys"),
76            proc: tmp.path().join("proc"),
77        };
78        assert_eq!(thread_count(&roots, 7), Some(3));
79        assert_eq!(thread_count(&roots, 8), None);
80    }
81}
rigtop_core/linux/procstat.rs

rigtop_core/linux/
procstat.rs
