Revert "Procstat: don't cache PIDs" (#2479)

plugins/inputs/procstat/procstat.go

@@ -8,6 +8,8 @@ import (
 	"strconv"
 	"strings"
 
+	"github.com/shirou/gopsutil/process"
+
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
 )
@@ -21,12 +23,15 @@ type Procstat struct {
 	User        string
 	PidTag      bool
 
+	// pidmap maps a pid to a process object, so we don't recreate every gather
+	pidmap map[int32]*process.Process
 	// tagmap maps a pid to a map of tags for that pid
 	tagmap map[int32]map[string]string
 }
 
 func NewProcstat() *Procstat {
 	return &Procstat{
+		pidmap: make(map[int32]*process.Process),
 		tagmap: make(map[int32]map[string]string),
 	}
 }
@@ -62,26 +67,51 @@ func (_ *Procstat) Description() string {
 }
 
 func (p *Procstat) Gather(acc telegraf.Accumulator) error {
-	pids, err := p.getAllPids()
+	err := p.createProcesses()
 	if err != nil {
 		log.Printf("E! Error: procstat getting process, exe: [%s] pidfile: [%s] pattern: [%s] user: [%s] %s",
 			p.Exe, p.PidFile, p.Pattern, p.User, err.Error())
 	} else {
-		for _, pid := range pids {
+		for pid, proc := range p.pidmap {
 			if p.PidTag {
 				p.tagmap[pid]["pid"] = fmt.Sprint(pid)
 			}
-			p := NewSpecProcessor(p.ProcessName, p.Prefix, pid, acc, p.tagmap[pid])
-			err := p.pushMetrics()
-			if err != nil {
-				log.Printf("E! Error: procstat: %s", err.Error())
-			}
+			p := NewSpecProcessor(p.ProcessName, p.Prefix, pid, acc, proc, p.tagmap[pid])
+			p.pushMetrics()
 		}
 	}
 
 	return nil
 }
 
+func (p *Procstat) createProcesses() error {
+	var errstring string
+	var outerr error
+
+	pids, err := p.getAllPids()
+	if err != nil {
+		errstring += err.Error() + " "
+	}
+
+	for _, pid := range pids {
+		_, ok := p.pidmap[pid]
+		if !ok {
+			proc, err := process.NewProcess(pid)
+			if err == nil {
+				p.pidmap[pid] = proc
+			} else {
+				errstring += err.Error() + " "
+			}
+		}
+	}
+
+	if errstring != "" {
+		outerr = fmt.Errorf("%s", errstring)
+	}
+
+	return outerr
+}
+
 func (p *Procstat) getAllPids() ([]int32, error) {
 	var pids []int32
 	var err error