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

CHANGELOG.md

@@ -61,8 +61,6 @@ be deprecated eventually.
 
 - [#2077](https://github.com/influxdata/telegraf/issues/2077): SQL Server Input - Arithmetic overflow error converting numeric to data type int.
 - [#2262](https://github.com/influxdata/telegraf/issues/2262): Flush jitter can inhibit metric collection.
-- [#2287](https://github.com/influxdata/telegraf/issues/2287): Kubernetes input: Handle null startTime for stopped pods
-- [#1636](https://github.com/influxdata/telegraf/issues/1636): procstat - stop caching PIDs.
 - [#2318](https://github.com/influxdata/telegraf/issues/2318): haproxy input - Add missing fields.
 - [#2287](https://github.com/influxdata/telegraf/issues/2287): Kubernetes input: Handle null startTime for stopped pods.
 - [#2356](https://github.com/influxdata/telegraf/issues/2356): cpu input panic when /proc/stat is empty.

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

plugins/inputs/procstat/procstat_test.go

@@ -6,6 +6,7 @@ import (
 	"strconv"
 	"testing"
 
+	"github.com/shirou/gopsutil/process"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
@@ -23,6 +24,7 @@ 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

@@ -1,7 +1,6 @@
 package procstat
 
 import (
-	"fmt"
 	"time"
 
 	"github.com/shirou/gopsutil/process"
@@ -10,7 +9,6 @@ import (
 )
 
 type SpecProcessor struct {
-	ProcessName string
 	Prefix string
 	pid    int32
 	tags   map[string]string
@@ -24,35 +22,29 @@ func NewSpecProcessor(
 	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() error {
+func (p *SpecProcessor) pushMetrics() {
 	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 + "_"
 	}
@@ -115,5 +107,4 @@ func (p *SpecProcessor) pushMetrics() error {
 	}
 
 	p.acc.AddFields("procstat", fields, p.tags)
-	return nil
 }