numcpus

README

numcpus

Package numcpus provides information about the number of CPUs in the system.

It gets the number of CPUs (online, offline, present, possible, configured or kernel maximum) on Linux, Darwin, FreeBSD, NetBSD, OpenBSD, DragonflyBSD or Solaris/Illumos systems.

On Linux, the information is retrieved by reading the corresponding CPU topology files in /sys/devices/system/cpu.

On BSD systems, the information is retrieved using the hw.ncpu and hw.ncpuonline sysctls, if supported.

Not all functions are supported on Darwin, FreeBSD, NetBSD, OpenBSD, DragonflyBSD and Solaris/Illumos. ErrNotSupported is returned in case a function is not supported on a particular platform.

Usage

package main

import (
	"fmt"
	"os"

	"github.com/tklauser/numcpus"
)

func main() {
	online, err := numcpus.GetOnline()
	if err != nil {
		fmt.Fprintf(os.Stderr, "GetOnline: %v\n", err)
	}
	fmt.Printf("online CPUs: %v\n", online)

	possible, err := numcpus.GetPossible()
	if err != nil {
		fmt.Fprintf(os.Stderr, "GetPossible: %v\n", err)
	}
	fmt.Printf("possible CPUs: %v\n", possible)
}

References

• Linux kernel sysfs documentation for CPU attributes
• Linux kernel CPU topology documentation

Documentation

Overview

Package numcpus provides information about the number of CPUs in the system.

It gets the number of CPUs (online, offline, present, possible or kernel maximum) on Linux, Darwin, FreeBSD, NetBSD, OpenBSD, DragonflyBSD, Solaris/Illumos or Windows systems.

On Linux, the information is retrieved by reading the corresponding CPU topology files in /sys/devices/system/cpu.

On BSD systems, the information is retrieved using the hw.ncpu and hw.ncpuonline sysctls, if supported.

On Windows systems, the information is retrieved using the GetActiveProcessorCount and GetMaximumProcessorCount functions, respectively.

Not all functions are supported on Darwin, FreeBSD, NetBSD, OpenBSD, DragonflyBSD, Solaris/Illumos and Windows. ErrNotSupported is returned in case a function is not supported on a particular platform.

Index

• Variables
• func GetConfigured() (int, error)
• func GetKernelMax() (int, error)
• func GetOffline() (int, error)
• func GetOnline() (int, error)
• func GetPossible() (int, error)
• func GetPresent() (int, error)

Examples

• GetOffline
• GetOnline
• GetPossible
• GetPresent

Variables

var ErrNotSupported = errors.New("function not supported")

ErrNotSupported is the error returned when the function is not supported.

Functions

func GetConfigured

func GetConfigured() (int, error)

GetConfigured returns the number of CPUs configured on the system. This function should return the same value as `getconf _SC_NPROCESSORS_CONF` on a unix system.

func GetKernelMax

func GetKernelMax() (int, error)

GetKernelMax returns the maximum number of CPUs allowed by the kernel configuration. This function is only supported on Linux and Windows systems.

func GetOffline

func GetOffline() (int, error)

GetOffline returns the number of offline CPUs, i.e. CPUs that are not online because they have been hotplugged off or exceed the limit of CPUs allowed by the kernel configuration (see GetKernelMax). This function is only supported on Linux systems.

Example

package main

import (
	"fmt"
	"os"

	"github.com/tklauser/numcpus"
)

func main() {
	offline, err := numcpus.GetOffline()
	if err != nil {
		fmt.Fprintf(os.Stderr, "GetOffline: %v\n", err)
	}
	fmt.Printf("# of offline CPUs: %v\n", offline)
}

func GetOnline

func GetOnline() (int, error)

GetOnline returns the number of CPUs that are online and being scheduled.

Example

package main

import (
	"fmt"
	"os"

	"github.com/tklauser/numcpus"
)

func main() {
	online, err := numcpus.GetOnline()
	if err != nil {
		fmt.Fprintf(os.Stderr, "GetOnline: %v\n", err)
	}
	fmt.Printf("# of online CPUs: %v\n", online)
}

func GetPossible

func GetPossible() (int, error)

GetPossible returns the number of possible CPUs, i.e. CPUs that have been allocated resources and can be brought online if they are present.

Example

package main

import (
	"fmt"
	"os"

	"github.com/tklauser/numcpus"
)

func main() {
	possible, err := numcpus.GetPossible()
	if err != nil {
		fmt.Fprintf(os.Stderr, "GetPossible: %v\n", err)
	}
	fmt.Printf("# of possible CPUs: %v\n", possible)
}

func GetPresent

func GetPresent() (int, error)

GetPresent returns the number of CPUs present in the system.

Example

package main

import (
	"fmt"
	"os"

	"github.com/tklauser/numcpus"
)

func main() {
	present, err := numcpus.GetPresent()
	if err != nil {
		fmt.Fprintf(os.Stderr, "GetPresent: %v\n", err)
	}
	fmt.Printf("# of present CPUs: %v\n", present)
}