1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139

// Copyright 2019-2022 Clemens Lutz
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Set the CPU core affinity of a thread.

use crate::error::{ErrorKind, Result};
use crate::runtime::linux_wrapper::CpuSet;
use std::default::Default;
use std::fs::File;
use std::io::Error as IoError;
use std::io::Read;
use std::path::Path;

#[derive(Clone)]
pub struct CpuAffinity {
    affinity_list: Vec<u16>,
}

impl CpuAffinity {
    /// Takes a slice containing CPU core affinities.
    pub fn from_slice(affinity_list: &[u16]) -> Self {
        Self {
            affinity_list: Vec::from(affinity_list),
        }
    }

    /// Reads a list of CPU core affinities from a file.
    ///
    /// CPU core affinities should be listed in a single line and separated with
    /// spaces. E.g.:
    ///
    /// ```ignore
    /// 0 2 4 6 1 3 5 7
    /// ```
    ///
    /// Lines that start with '#' are ignored as comments.
    ///
    pub fn from_file(path: &Path) -> Result<Self> {
        let mut file = File::open(path)?;
        let mut contents = String::new();
        file.read_to_string(&mut contents)?;

        let affinity_list = contents
            .lines()
            .filter(|line| !line.starts_with('#'))
            .take(1)
            .flat_map(|line| line.split_whitespace())
            .filter_map(|item| item.parse::<u16>().ok())
            .collect();

        Ok(Self { affinity_list })
    }

    /// Maps a thread ID to a CPU core ID.
    ///
    /// Returns a CPU core ID, or `None` if the thread ID is out-of-bounds.
    /// Core IDs are guaranteed to be in the order given on construction.
    ///
    pub fn thread_to_cpu(&self, tid: u16) -> Option<u16> {
        let index: usize = tid.into();
        self.affinity_list.get(index).map(|&tid| tid)
    }

    /// Binds the current thread to the CPU core by the given thread ID.
    ///
    /// Core IDs are guaranteed to be in the order given on construction.
    ///
    pub fn set_affinity(&self, tid: u16) -> Result<()> {
        let core_id = self
            .thread_to_cpu(tid)
            .ok_or_else(|| ErrorKind::InvalidArgument("Thread ID is out-of-bounds".to_string()))?;

        let mut cpu_set = CpuSet::new();
        cpu_set.add(core_id);

        unsafe {
            if libc::sched_setaffinity(
                0,
                cpu_set.bytes(),
                cpu_set.as_slice().as_ptr() as *const libc::cpu_set_t,
            ) == -1
            {
                Err(ErrorKind::Io(IoError::last_os_error()))?
            }
        }

        Ok(())
    }

    /// Returns the number of CPU core IDs currently stored in the mapping.
    pub fn len(&self) -> usize {
        self.affinity_list.len()
    }

    /// Returns the CPU core ID that the calling thread is currently running on.
    pub fn get_cpu() -> Result<u16> {
        unsafe {
            match libc::sched_getcpu() {
                -1 => Err(ErrorKind::Io(IoError::last_os_error()))?,
                cpu_id => Ok(cpu_id as u16),
            }
        }
    }
}

impl Default for CpuAffinity {
    fn default() -> Self {
        let mut cpu_set = CpuSet::new();

        unsafe {
            if libc::sched_getaffinity(
                0,
                cpu_set.bytes(),
                cpu_set.as_mut_slice().as_mut_ptr() as *mut libc::cpu_set_t,
            ) == -1
            {
                Err(ErrorKind::Io(IoError::last_os_error()))
                    .expect("Couldn't get the list of available CPU affinities from the OS")
            }
        }

        let affinity_list: Vec<_> = (0..cpu_set.max_id())
            .filter(|&cpu_id| cpu_set.is_set(cpu_id))
            .collect();

        Self { affinity_list }
    }
}