Determine number of cores using Rust

Question

I want to spawn a certain number of tasks based on the cores that a machine has. Is there anything in Rust that can find the number of cores, or should I just run external commands and parse the output?

Answer 1

There's now a crate to do this: https://crates.io/crates/num_cpus

Add this to your Cargo.toml:

[dependencies]
num_cpus = "0.2"

Then in your source:

extern crate num_cpus;
let num = num_cpus::get();

Answer 2

You could use std::os::num_cpus. Example:

fn main() {
    println!("{}", std::os::num_cpus());
}

Answer 3

You can use std::thread::available_parallelism as of Rust 1.59.0:

use std::thread::available_parallelism;
let default_parallelism_approx = available_parallelism().unwrap().get();

It returns 12 on my machine with a Ryzen 5 4600H which is quite consistent with the number of logical processors it has.

Answer 4

It is now possible to use:

std::os::num_cpus

pub fn num_cpus() -> uint

---

Version of Rust:

$ rustc --version
rustc 0.13.0-nightly (d91a015ab 2014-11-14 23:37:27 +0000)

Reference:

std::os::num_cpus