Flaky shim test (#7656)

plugins/inputs/execd/shim/goshim.go

@@ -106,7 +106,7 @@ func (s *Shim) Run(pollInterval time.Duration) error {
 		}
 		gatherPromptCh := make(chan empty, 1)
 		s.gatherPromptChans = append(s.gatherPromptChans, gatherPromptCh)
-		wg.Add(1)
+		wg.Add(1) // one per input
 		go func(input telegraf.Input) {
 			startGathering(ctx, input, acc, gatherPromptCh, pollInterval)
 			if serviceInput, ok := input.(telegraf.ServiceInput); ok {
@@ -216,11 +216,7 @@ func startGathering(ctx context.Context, input telegraf.Input, acc telegraf.Accu
 		select {
 		case <-ctx.Done():
 			return
-		case _, open := <-gatherPromptCh:
-			if !open {
-				// stdin has closed.
-				return
-			}
+		case <-gatherPromptCh:
 			if err := input.Gather(acc); err != nil {
 				fmt.Fprintf(os.Stderr, "failed to gather metrics: %s", err)
 			}

plugins/inputs/execd/shim/shim_posix_test.go

@@ -51,13 +51,7 @@ func TestShimUSR1SignalingWorks(t *testing.T) {
 		}
 	}()
 
-	timeout := time.NewTimer(10 * time.Second)
-
-	select {
-	case <-metricProcessed:
-	case <-timeout.C:
-		require.Fail(t, "Timeout waiting for metric to arrive")
-	}
+	<-metricProcessed
 	cancel()
 
 	r := bufio.NewReader(stdoutReader)
@@ -66,5 +60,7 @@ func TestShimUSR1SignalingWorks(t *testing.T) {
 	require.Equal(t, "measurement,tag=tag field=1i 1234000005678\n", out)
 
 	stdinWriter.Close()
+	readUntilEmpty(r)
+
 	<-exited
 }

plugins/inputs/execd/shim/shim_test.go

@@ -21,23 +21,13 @@ func TestShimWorks(t *testing.T) {
 
 	stdin, _ = io.Pipe() // hold the stdin pipe open
 
-	timeout := time.NewTimer(10 * time.Second)
 	metricProcessed, _ := runInputPlugin(t, 10*time.Millisecond)
 
-	select {
-	case <-metricProcessed:
-	case <-timeout.C:
-		require.Fail(t, "Timeout waiting for metric to arrive")
-	}
+	<-metricProcessed
 	for stdoutBytes.Len() == 0 {
-		select {
-		case <-timeout.C:
-			require.Fail(t, "Timeout waiting to read metric from stdout")
-			return
-		default:
+		t.Log("Waiting for bytes available in stdout")
 		time.Sleep(10 * time.Millisecond)
 	}
-	}
 
 	out := string(stdoutBytes.Bytes())
 	require.Contains(t, out, "\n")
@@ -52,16 +42,11 @@ func TestShimStdinSignalingWorks(t *testing.T) {
 	stdin = stdinReader
 	stdout = stdoutWriter
 
-	timeout := time.NewTimer(10 * time.Second)
 	metricProcessed, exited := runInputPlugin(t, 40*time.Second)
 
 	stdinWriter.Write([]byte("\n"))
 
-	select {
-	case <-metricProcessed:
-	case <-timeout.C:
-		require.Fail(t, "Timeout waiting for metric to arrive")
-	}
+	<-metricProcessed
 
 	r := bufio.NewReader(stdoutReader)
 	out, err := r.ReadString('\n')
@@ -69,12 +54,15 @@ func TestShimStdinSignalingWorks(t *testing.T) {
 	require.Equal(t, "measurement,tag=tag field=1i 1234000005678\n", out)
 
 	stdinWriter.Close()
+
+	readUntilEmpty(r)
+
 	// check that it exits cleanly
 	<-exited
 }
 
 func runInputPlugin(t *testing.T, interval time.Duration) (metricProcessed chan bool, exited chan bool) {
-	metricProcessed = make(chan bool)
+	metricProcessed = make(chan bool, 10)
 	exited = make(chan bool)
 	inp := &testInput{
 		metricProcessed: metricProcessed,
@@ -172,3 +160,15 @@ func (i *serviceInput) Start(acc telegraf.Accumulator) error {
 
 func (i *serviceInput) Stop() {
 }
+
+// we can get stuck if stdout gets clogged up and nobody's reading from it.
+// make sure we keep it going
+func readUntilEmpty(r *bufio.Reader) {
+	go func() {
+		var err error
+		for err != io.EOF {
+			_, err = r.ReadString('\n')
+			time.Sleep(10 * time.Millisecond)
+		}
+	}()
+}