Procstat: don't cache PIDs

Changed the procstat input plugin to not cache PIDs. Solves influxdata#1636.
The logic of creating a process by pid was moved from `procstat.go` to
`spec_processor.go`.

plugins/inputs/procstat/procstat.go

@@ -8,8 +8,6 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/shirou/gopsutil/process"
-
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
 )
@@ -23,15 +21,12 @@ 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),
 	}
 }
@@ -67,49 +62,24 @@ func (_ *Procstat) Description() string {
 }
 
 func (p *Procstat) Gather(acc telegraf.Accumulator) error {
-	err := p.createProcesses()
+	pids, err := p.getAllPids()
 	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, proc := range p.pidmap {
+		for _, pid := range pids {
 			if p.PidTag {
 				p.tagmap[pid]["pid"] = fmt.Sprint(pid)
 			}
-			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() + " "
+			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())
 			}
 		}
 	}
 
-	if errstring != "" {
-		outerr = fmt.Errorf("%s", errstring)
-	}
-
-	return outerr
+	return nil
 }
 
 func (p *Procstat) getAllPids() ([]int32, error) {

plugins/inputs/procstat/procstat_test.go

@@ -6,7 +6,6 @@ import (
 	"strconv"
 	"testing"
 
-	"github.com/shirou/gopsutil/process"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
@@ -24,7 +23,6 @@ func TestGather(t *testing.T) {
 	p := Procstat{
 		PidFile: file.Name(),
 		Prefix:  "foo",
-		pidmap:  make(map[int32]*process.Process),
 		tagmap:  make(map[int32]map[string]string),
 	}
 	p.Gather(&acc)

plugins/inputs/procstat/spec_processor.go

@@ -2,49 +2,57 @@ package procstat
 
 import (
 	"time"
+	"fmt"
 
 	"github.com/shirou/gopsutil/process"
 
 	"github.com/influxdata/telegraf"
 )
 
 type SpecProcessor struct {
-	Prefix string
-	pid    int32
-	tags   map[string]string
-	fields map[string]interface{}
-	acc    telegraf.Accumulator
-	proc   *process.Process
+	ProcessName string
+	Prefix      string
+	pid         int32
+	tags        map[string]string
+	fields      map[string]interface{}
+	acc         telegraf.Accumulator
+	proc        *process.Process
 }
 
 func NewSpecProcessor(
 	processName string,
 	prefix string,
 	pid int32,
 	acc telegraf.Accumulator,
-	p *process.Process,
 	tags map[string]string,
 ) *SpecProcessor {
-	if processName != "" {
-		tags["process_name"] = processName
-	} else {
-		name, err := p.Name()
-		if err == nil {
-			tags["process_name"] = name
-		}
-	}
 	return &SpecProcessor{
+		ProcessName: processName,
 		Prefix: prefix,
 		pid:    pid,
 		tags:   tags,
 		fields: make(map[string]interface{}),
 		acc:    acc,
-		proc:   p,
 	}
 }
 
-func (p *SpecProcessor) pushMetrics() {
+func (p *SpecProcessor) pushMetrics() (error) {
 	var prefix string
+	proc, err := process.NewProcess(p.pid)
+	if err != nil {
+		return fmt.Errorf("Failed to open process with pid '%d'. Error: '%s'",
+			p.pid, err)
+	}
+	p.proc = proc
+	if p.ProcessName != "" {
+		p.tags["process_name"] = p.ProcessName
+	} else {
+		name, err := p.proc.Name()
+		if err == nil {
+			p.tags["process_name"] = name
+		}
+	}
+
 	if p.Prefix != "" {
 		prefix = p.Prefix + "_"
 	}
@@ -107,4 +115,5 @@ func (p *SpecProcessor) pushMetrics() {
 	}
 
 	p.acc.AddFields("procstat", fields, p.tags)
+	return nil
 }