dotcloud/docker

package sysinfo // import "github.com/docker/docker/pkg/sysinfo"

import (
    "unsafe"

    "golang.org/x/sys/windows"
)

var (
    kernel32               = windows.NewLazySystemDLL("kernel32.dll")
    getCurrentProcess      = kernel32.NewProc("GetCurrentProcess")
    getProcessAffinityMask = kernel32.NewProc("GetProcessAffinityMask")
)

// Returns bit count of 1, used by NumCPU
func popcnt(x uint64) (n byte) {
    x -= (x >> 1) & 0x5555555555555555
    x = (x>>2)&0x3333333333333333 + x&0x3333333333333333
    x += x >> 4
    x &= 0x0f0f0f0f0f0f0f0f
    x *= 0x0101010101010101
    return byte(x >> 56)
}

func numCPU() int {
    // Gets the affinity mask for a process
    var mask, sysmask uintptr
    currentProcess, _, _ := getCurrentProcess.Call()
    ret, _, _ := getProcessAffinityMask.Call(currentProcess, uintptr(unsafe.Pointer(&mask)), uintptr(unsafe.Pointer(&sysmask)))
    if ret == 0 {
        return 0
    }
    // For every available thread a bit is set in the mask.
    ncpu := int(popcnt(uint64(mask)))
    return ncpu
}