New object: ErrChan for concurrent err handling

internal/errchan/errchan.go

@@ -0,0 +1,37 @@
+package errchan
+
+import (
+	"fmt"
+	"strings"
+)
+
+type ErrChan struct {
+	C chan error
+}
+
+// New returns an error channel of max length 'n'
+// errors can be sent to the ErrChan.C channel, and will be returned when
+// ErrChan.Error() is called.
+func New(n int) *ErrChan {
+	return &ErrChan{
+		C: make(chan error, n),
+	}
+}
+
+// Error closes the ErrChan.C channel and returns an error if there are any
+// non-nil errors, otherwise returns nil.
+func (e *ErrChan) Error() error {
+	close(e.C)
+
+	var out string
+	for err := range e.C {
+		if err != nil {
+			out += "[" + err.Error() + "], "
+		}
+	}
+
+	if out != "" {
+		return fmt.Errorf("Errors encountered: " + strings.TrimRight(out, ", "))
+	}
+	return nil
+}

plugins/inputs/cloudwatch/cloudwatch.go

@@ -3,6 +3,7 @@ package cloudwatch
 import (
 	"fmt"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -12,6 +13,7 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
 	internalaws "github.com/influxdata/telegraf/internal/config/aws"
+	"github.com/influxdata/telegraf/internal/errchan"
 	"github.com/influxdata/telegraf/internal/limiter"
 	"github.com/influxdata/telegraf/plugins/inputs"
 )
@@ -166,7 +168,7 @@ func (c *CloudWatch) Gather(acc telegraf.Accumulator) error {
 	}
 
 	metricCount := len(metrics)
-	var errChan = make(chan error, metricCount)
+	errChan := errchan.New(metricCount)
 
 	now := time.Now()
 
@@ -175,18 +177,18 @@ func (c *CloudWatch) Gather(acc telegraf.Accumulator) error {
 	// http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/cloudwatch_limits.html
 	lmtr := limiter.NewRateLimiter(10, time.Second)
 	defer lmtr.Stop()
+	var wg sync.WaitGroup
+	wg.Add(len(metrics))
 	for _, m := range metrics {
 		<-lmtr.C
-		go c.gatherMetric(acc, m, now, errChan)
+		go func(inm *cloudwatch.Metric) {
+			defer wg.Done()
+			c.gatherMetric(acc, inm, now, errChan.C)
+		}(m)
 	}
+	wg.Wait()
 
-	for i := 1; i <= metricCount; i++ {
-		err := <-errChan
-		if err != nil {
-			return err
-		}
-	}
-	return nil
+	return errChan.Error()
 }
 
 func init() {

plugins/inputs/elasticsearch/elasticsearch.go

@@ -2,14 +2,13 @@ package elasticsearch
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
 	"net/http"
-	"strings"
 	"sync"
 	"time"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/errchan"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	jsonparser "github.com/influxdata/telegraf/plugins/parsers/json"
 )
@@ -102,7 +101,7 @@ func (e *Elasticsearch) Description() string {
 // Gather reads the stats from Elasticsearch and writes it to the
 // Accumulator.
 func (e *Elasticsearch) Gather(acc telegraf.Accumulator) error {
-	errChan := make(chan error, len(e.Servers))
+	errChan := errchan.New(len(e.Servers))
 	var wg sync.WaitGroup
 	wg.Add(len(e.Servers))
 
@@ -116,7 +115,7 @@ func (e *Elasticsearch) Gather(acc telegraf.Accumulator) error {
 				url = s + statsPath
 			}
 			if err := e.gatherNodeStats(url, acc); err != nil {
-				errChan <- err
+				errChan.C <- err
 				return
 			}
 			if e.ClusterHealth {
@@ -126,17 +125,7 @@ func (e *Elasticsearch) Gather(acc telegraf.Accumulator) error {
 	}
 
 	wg.Wait()
-	close(errChan)
-	// Get all errors and return them as one giant error
-	errStrings := []string{}
-	for err := range errChan {
-		errStrings = append(errStrings, err.Error())
-	}
-
-	if len(errStrings) == 0 {
-		return nil
-	}
-	return errors.New(strings.Join(errStrings, "\n"))
+	return errChan.Error()
 }
 
 func (e *Elasticsearch) gatherNodeStats(url string, acc telegraf.Accumulator) error {

plugins/inputs/exec/exec.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal"
+	"github.com/influxdata/telegraf/internal/errchan"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	"github.com/influxdata/telegraf/plugins/parsers"
 	"github.com/influxdata/telegraf/plugins/parsers/nagios"
@@ -182,23 +183,15 @@ func (e *Exec) Gather(acc telegraf.Accumulator) error {
 		}
 	}
 
-	e.errChan = make(chan error, len(commands))
+	errChan := errchan.New(len(commands))
+	e.errChan = errChan.C
 
 	e.wg.Add(len(commands))
 	for _, command := range commands {
 		go e.ProcessCommand(command, acc)
 	}
 	e.wg.Wait()
-
-	select {
-	default:
-		close(e.errChan)
-		return nil
-	case err := <-e.errChan:
-		close(e.errChan)
-		return err
-	}
-
+	return errChan.Error()
 }
 
 func init() {

plugins/inputs/haproxy/haproxy.go

@@ -3,17 +3,18 @@ package haproxy
 import (
 	"encoding/csv"
 	"fmt"
-	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/plugins/inputs"
 	"io"
-	"log"
 	"net"
 	"net/http"
 	"net/url"
 	"strconv"
 	"strings"
 	"sync"
 	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/errchan"
+	"github.com/influxdata/telegraf/plugins/inputs"
 )
 
 //CSV format: https://cbonte.github.io/haproxy-dconv/configuration-1.5.html#9.1
@@ -114,18 +115,17 @@ func (g *haproxy) Gather(acc telegraf.Accumulator) error {
 	}
 
 	var wg sync.WaitGroup
+	errChan := errchan.New(len(g.Servers))
+	wg.Add(len(g.Servers))
 	for _, server := range g.Servers {
-		wg.Add(1)
 		go func(serv string) {
 			defer wg.Done()
-			if err := g.gatherServer(serv, acc); err != nil {
-				log.Printf("HAProxy error gathering server: %s, %s", serv, err)
-			}
+			errChan.C <- g.gatherServer(serv, acc)
 		}(server)
 	}
 
 	wg.Wait()
-	return nil
+	return errChan.Error()
 }
 
 func (g *haproxy) gatherServerSocket(addr string, acc telegraf.Accumulator) error {

plugins/inputs/rabbitmq/rabbitmq.go

@@ -5,9 +5,11 @@ import (
 	"fmt"
 	"net/http"
 	"strconv"
+	"sync"
 	"time"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/errchan"
 	"github.com/influxdata/telegraf/plugins/inputs"
 )
 
@@ -129,20 +131,18 @@ func (r *RabbitMQ) Gather(acc telegraf.Accumulator) error {
 		}
 	}
 
-	var errChan = make(chan error, len(gatherFunctions))
-
+	var wg sync.WaitGroup
+	wg.Add(len(gatherFunctions))
+	errChan := errchan.New(len(gatherFunctions))
 	for _, f := range gatherFunctions {
-		go f(r, acc, errChan)
+		go func(gf gatherFunc) {
+			defer wg.Done()
+			gf(r, acc, errChan.C)
+		}(f)
 	}
+	wg.Wait()
 
-	for i := 1; i <= len(gatherFunctions); i++ {
-		err := <-errChan
-		if err != nil {
-			return err
-		}
-	}
-
-	return nil
+	return errChan.Error()
 }
 
 func (r *RabbitMQ) requestJSON(u string, target interface{}) error {