Refactor procstat input (#2540)

fixes #1636 
fixes #2315

plugins/inputs/procstat/process.go

@@ -0,0 +1,60 @@
+package procstat
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/shirou/gopsutil/cpu"
+	"github.com/shirou/gopsutil/process"
+)
+
+type Process interface {
+	PID() PID
+	Tags() map[string]string
+
+	IOCounters() (*process.IOCountersStat, error)
+	MemoryInfo() (*process.MemoryInfoStat, error)
+	Name() (string, error)
+	NumCtxSwitches() (*process.NumCtxSwitchesStat, error)
+	NumFDs() (int32, error)
+	NumThreads() (int32, error)
+	Percent(interval time.Duration) (float64, error)
+	Times() (*cpu.TimesStat, error)
+}
+
+type Proc struct {
+	hasCPUTimes bool
+	tags        map[string]string
+	*process.Process
+}
+
+func NewProc(pid PID) (Process, error) {
+	process, err := process.NewProcess(int32(pid))
+	if err != nil {
+		return nil, err
+	}
+
+	proc := &Proc{
+		Process:     process,
+		hasCPUTimes: false,
+		tags:        make(map[string]string),
+	}
+	return proc, nil
+}
+
+func (p *Proc) Tags() map[string]string {
+	return p.tags
+}
+
+func (p *Proc) PID() PID {
+	return PID(p.Process.Pid)
+}
+
+func (p *Proc) Percent(interval time.Duration) (float64, error) {
+	cpu_perc, err := p.Process.Percent(time.Duration(0))
+	if !p.hasCPUTimes && err == nil {
+		p.hasCPUTimes = true
+		return 0, fmt.Errorf("Must call Percent twice to compute percent cpu.")
+	}
+	return cpu_perc, err
+}