Processor

Check available parallelism

Queries the amount of parallelism available to the current process with std::thread::available_parallelism. This returns the parallelism the program can actually use: it honors CPU affinity masks and container limits such as Linux cgroup quotas. The result is a NonZeroUsize, so it is guaranteed to be at least 1, and it is wrapped in an io::Result because the value cannot always be determined. This has been available in the standard library since Rust 1.59, making it a good default for sizing thread pools.

use std::thread::available_parallelism;

fn main() -> std::io::Result<()> {
    let count = available_parallelism()?.get();
    println!("Number of available threads is {}", count);
    Ok(())
}

Check number of logical cpu cores

Shows the number of logical CPU cores in current machine using num_cpus::get.

This differs from std::thread::available_parallelism above: num_cpus::get reports the total number of logical cores on the machine, whereas available_parallelism reports only the parallelism available to the current process, accounting for CPU affinity masks and container limits such as Linux cgroup quotas. num_cpus::get also returns a plain usize rather than a Result, so it needs no error handling, and num_cpus::get_physical additionally exposes the count of physical cores, which the standard library does not provide.

fn main() {
    println!("Number of logical cores is {}", num_cpus::get());
}