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// TODO(thaJeztah): remove once we are a module; the go:build directive prevents go from downgrading language version to go1.16:
//go:build go1.23
package platform
import (
"os"
"strconv"
"strings"
"sync"
)
// possibleCPUs returns the set of possible CPUs on the host (which is
// equal or larger to the number of CPUs currently online). The returned
// set may be a single number ({0}), or a continuous range ({0,1,2,3}), or
// a non-continuous range ({0,1,2,3,12,13,14,15})
//
// Returns nil on errors. Assume CPUs are 0 -> runtime.NumCPU() in that case.
var possibleCPUs = sync.OnceValue(func() []int {
data, err := os.ReadFile("/sys/devices/system/cpu/possible")
if err != nil {
return nil
}
content := strings.TrimSpace(string(data))
return parsePossibleCPUs(content)
})
func parsePossibleCPUs(content string) []int {
ranges := strings.Split(content, ",")
var cpus []int
for _, r := range ranges {
// Each entry is either a single number (e.g., "0") or a continuous range
// (e.g., "0-3").
if rStart, rEnd, ok := strings.Cut(r, "-"); !ok {
cpu, err := strconv.Atoi(rStart)
if err != nil {
return nil
}
cpus = append(cpus, cpu)
} else {
var start, end int
start, err := strconv.Atoi(rStart)
if err != nil {
return nil
}
end, err = strconv.Atoi(rEnd)
if err != nil {
return nil
}
for i := start; i <= end; i++ {
cpus = append(cpus, i)
}
}
}
return cpus
}
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