[load][darwin] Remove calls to sysctl binary in load/load_darwin.go #639

Again, a simple benchmark:

Lomanics-iMac:~ lomanic$ time ./load_avg.old ; time ./load_avg
{load1:0.89,load5:0.99,load15:1.01} <nil>

real    0m0.019s
user    0m0.008s
sys     0m0.013s
{load1:0.8876953125,load5:0.98828125,load15:1.0146484375} <nil>

real    0m0.011s
user    0m0.004s
sys     0m0.006s

This is faster and yields more precise results.

load/load_darwin.go

@@ -5,10 +5,10 @@ package load
 import (
 	"context"
 	"os/exec"
-	"strconv"
 	"strings"
+	"unsafe"
 
-	"github.com/shirou/gopsutil/internal/common"
+	"golang.org/x/sys/unix"
 )
 
 func Avg() (*AvgStat, error) {
@@ -16,28 +16,23 @@ func Avg() (*AvgStat, error) {
 }
 
 func AvgWithContext(ctx context.Context) (*AvgStat, error) {
-	values, err := common.DoSysctrlWithContext(ctx, "vm.loadavg")
+	// This SysctlRaw method borrowed from
+	// https://github.com/prometheus/node_exporter/blob/master/collector/loadavg_freebsd.go
+	// this implementation is common with BSDs
+	type loadavg struct {
+		load  [3]uint32
+		scale int
+	}
+	b, err := unix.SysctlRaw("vm.loadavg")
 	if err != nil {
 		return nil, err
 	}
-
-	load1, err := strconv.ParseFloat(values[0], 64)
-	if err != nil {
-		return nil, err
-	}
-	load5, err := strconv.ParseFloat(values[1], 64)
-	if err != nil {
-		return nil, err
-	}
-	load15, err := strconv.ParseFloat(values[2], 64)
-	if err != nil {
-		return nil, err
-	}
-
+	load := *(*loadavg)(unsafe.Pointer((&b[0])))
+	scale := float64(load.scale)
 	ret := &AvgStat{
-		Load1:  float64(load1),
-		Load5:  float64(load5),
-		Load15: float64(load15),
+		Load1:  float64(load.load[0]) / scale,
+		Load5:  float64(load.load[1]) / scale,
+		Load15: float64(load.load[2]) / scale,
 	}
 
 	return ret, nil