Get the number of CPU cores available on the system.

cpu

cpus

core

processor

hardware

system

moon add justjavac/num_cpus@0.1.9

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Author

justjavac

Version

0.1.9

License

MIT

Repository

github.com/justjavac/moonbit-num-cpus

Last updated

2 months ago

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README

#moonbit-num-cpus

moonbit-num-cpus is a small MoonBit module for detecting the number of CPU cores available on the current machine.

It supports:

Logical CPU count, including SMT / hyper-threading
Physical CPU count when the operating system can report it
Native implementations for Windows, macOS, Linux, and other Unix-like systems
Safe fallback behavior that never returns less than 1

#Installation

moon add justjavac/num_cpus

#API

Function	Description
@num_cpus.get()	Returns the number of logical CPU cores
@num_cpus.get_physical()	Returns the number of physical CPU cores, or a fallback value when exact detection is unavailable

#Usage

fn main {
  let logical = @num_cpus.get()
  let physical = @num_cpus.get_physical()

  println("Logical CPU cores: \{logical}")
  println("Physical CPU cores: \{physical}")

  if logical > physical {
    println("SMT or hyper-threading is likely enabled")
  }
}

#Common Use Cases

#Size a thread pool

fn worker_count() -> Int {
  @num_cpus.get_physical()
}

#Compare logical and physical cores

fn main {
  let logical = @num_cpus.get()
  let physical = @num_cpus.get_physical()
  println("CPU topology: \{physical} physical / \{logical} logical")
}

#Platform Support

Platform	Logical CPUs	Physical CPUs	Implementation
Windows	Yes	Yes	GetSystemInfo and GetLogicalProcessorInformation
macOS	Yes	Yes	sysconf and sysctl
Linux	Yes	Yes	sysconf and /proc/cpuinfo
Other Unix-like systems	Yes	Fallback	sysconf, with physical count falling back to logical count

#How It Works

Logical CPU detection uses native platform APIs rather than external commands.
Physical CPU detection uses the best available system interface on each OS.
When physical core detection is unavailable, the module falls back to the logical CPU count.
The package is designed for the native target and declares it as the preferred target.

#Development

moon test --target native
moon check --deny-warn --target native

#License

MIT. See LICENSE.

#Acknowledgments

Inspired by Rust's num_cpus crate.

#
get

source

fn get() -> Int

Get the number of CPU cores available on the system.

This function returns the number of logical CPU cores, which includes hyperthreading cores if available. For example, on a quad-core processor with hyperthreading, this would return 8.

The function uses FFI (Foreign Function Interface) to call native system APIs to retrieve the CPU count information.

Returns:

The number of logical CPU cores available on the system.

Example:

let logical_cores = @num_cpus.get()
println("Logical CPU cores: \{logical_cores}")

Note:

On multi-threaded systems, this includes all logical cores
The result is cached by the operating system and reflects the current hardware configuration
This function is thread-safe

#
get_physical

source

fn get_physical() -> Int

Get the number of physical CPU cores on the system.

This function returns the number of physical CPU cores, excluding hyperthreading. For example, on a quad-core processor with hyperthreading, this would return 4 (the actual physical cores), not 8.

The function uses FFI to call native system APIs that can distinguish between physical and logical cores.

Returns:

The number of physical CPU cores (not including hyperthreading).

Example:

let physical_cores = @num_cpus.get_physical()
let logical_cores = @num_cpus.get()
println("Physical cores: \{physical_cores}")
println("Logical cores: \{logical_cores}")
println("Hyperthreading ratio: \{logical_cores / physical_cores}")