fix datarace in input apache plugin

plugins/inputs/apache/apache.go

@@ -8,7 +8,6 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
-	"sync"
 	"time"
 
 	"github.com/influxdata/telegraf"
@@ -38,8 +37,8 @@ func (n *Apache) Gather(acc telegraf.Accumulator) error {
 		n.Urls = []string{"http://localhost/server-status?auto"}
 	}
 
-	var wg sync.WaitGroup
 	var outerr error
+	var errch = make(chan error)
 
 	for _, u := range n.Urls {
 		addr, err := url.Parse(u)
@@ -47,14 +46,17 @@ func (n *Apache) Gather(acc telegraf.Accumulator) error {
 			return fmt.Errorf("Unable to parse address '%s': %s", u, err)
 		}
 
-		wg.Add(1)
 		go func(addr *url.URL) {
-			defer wg.Done()
+			errch <- n.gatherUrl(addr, acc)
-			outerr = n.gatherUrl(addr, acc)
 		}(addr)
 	}
 
-	wg.Wait()
+	// Drain channel, waiting for all requests to finish and save last error.
+	for range n.Urls {
+		if err := <-errch; err != nil {
+			outerr = err
+		}
+	}
 
 	return outerr
 }

plugins/inputs/apache/apache_test.go

@@ -36,7 +36,8 @@ func TestHTTPApache(t *testing.T) {
 	defer ts.Close()
 
 	a := Apache{
-		Urls: []string{ts.URL},
+		// Fetch it 2 times to catch possible data races.
+		Urls: []string{ts.URL, ts.URL},
 	}
 
 	var acc testutil.Accumulator