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package main
import (
"bufio"
"errors"
"fmt"
"os"
"os/exec"
"strings"
)
var CgroupPath = "/sys/fs/cgroup/"
type CpuContext struct {
cpuAllocator *CpuAllocatorT
cpus []int
}
func (c *CpuContext) Release() {
c.cpuAllocator.cpus = append(c.cpuAllocator.cpus, c.cpus...)
c.cpus = c.cpus[:0] // empty the list
}
type CpuAllocatorT struct {
cpus []int
}
var cpuAllocator *CpuAllocatorT = nil
func (c *CpuAllocatorT) Allocate(nCpus int) (*CpuContext, error) {
var cpuCtx CpuContext
if len(c.cpus) < nCpus {
return nil, fmt.Errorf("could not allocate %d CPUs; available: %d", nCpus, len(c.cpus))
}
cpuCtx.cpus = c.cpus[0:nCpus]
cpuCtx.cpuAllocator = c
c.cpus = c.cpus[nCpus:]
return &cpuCtx, nil
}
func (c *CpuAllocatorT) readCpus() error {
var first, last int
// Path depends on cgroup version. We need to check which version is in use.
// For that following command can be used: 'stat -fc %T /sys/fs/cgroup/'
// In case the output states 'cgroup2fs' then cgroups v2 is used, 'tmpfs' in case cgroups v1.
cmd := exec.Command("stat", "-fc", "%T", "/sys/fs/cgroup/")
byteOutput, err := cmd.CombinedOutput()
if err != nil {
return err
}
CpuPath := CgroupPath
if strings.Contains(string(byteOutput), "tmpfs") {
CpuPath += "cpuset/cpuset.effective_cpus"
} else if strings.Contains(string(byteOutput), "cgroup2fs") {
CpuPath += "cpuset.cpus.effective"
} else {
return errors.New("cgroup unknown fs: " + string(byteOutput))
}
file, err := os.Open(CpuPath)
if err != nil {
return err
}
defer file.Close()
sc := bufio.NewScanner(file)
sc.Scan()
line := sc.Text()
_, err = fmt.Sscanf(line, "%d-%d", &first, &last)
if err != nil {
return err
}
for i := first; i <= last; i++ {
c.cpus = append(c.cpus, i)
}
return nil
}
func CpuAllocator() (*CpuAllocatorT, error) {
if cpuAllocator == nil {
cpuAllocator = new(CpuAllocatorT)
err := cpuAllocator.readCpus()
if err != nil {
return nil, err
}
}
return cpuAllocator, nil
}
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