Fix BatchSpanProcessor.Shutdown to wait until all spans are processed (#766)

* Fix BatchSpanProcessor.Shutdown to wait until all spans are processed

Currently it exits too soon - before drainQueue is finished

* Check bsp.stopCh to reliably drop span when batcher is stopped

* Enable tests

* Always use WithBlocking

Co-authored-by: Joshua MacDonald <jmacd@users.noreply.github.com>

sdk/trace/batch_span_processor.go

@@ -105,9 +105,10 @@ func NewBatchSpanProcessor(e export.SpanBatcher, opts ...BatchSpanProcessorOptio
 		queue:  make(chan *export.SpanData, o.MaxQueueSize),
 		stopCh: make(chan struct{}),
 	}
-	bsp.stopWait.Add(1)
 
+	bsp.stopWait.Add(1)
 	go func() {
+		defer bsp.stopWait.Done()
 		bsp.processQueue()
 		bsp.drainQueue()
 	}()
@@ -130,8 +131,6 @@ func (bsp *BatchSpanProcessor) Shutdown() {
 	bsp.stopOnce.Do(func() {
 		close(bsp.stopCh)
 		bsp.stopWait.Wait()
-		close(bsp.queue)
-
 	})
 }
 
@@ -173,7 +172,6 @@ func (bsp *BatchSpanProcessor) exportSpans() {
 // is shut down. It calls the exporter in batches of up to MaxExportBatchSize
 // waiting up to BatchTimeout to form a batch.
 func (bsp *BatchSpanProcessor) processQueue() {
-	defer bsp.stopWait.Done()
 	defer bsp.timer.Stop()
 
 	for {
@@ -197,13 +195,22 @@ func (bsp *BatchSpanProcessor) processQueue() {
 // drainQueue awaits the any caller that had added to bsp.stopWait
 // to finish the enqueue, then exports the final batch.
 func (bsp *BatchSpanProcessor) drainQueue() {
-	for sd := range bsp.queue {
-		bsp.batch = append(bsp.batch, sd)
-		if len(bsp.batch) == bsp.o.MaxExportBatchSize {
-			bsp.exportSpans()
+	for {
+		select {
+		case sd := <-bsp.queue:
+			if sd == nil {
+				bsp.exportSpans()
+				return
+			}
+
+			bsp.batch = append(bsp.batch, sd)
+			if len(bsp.batch) == bsp.o.MaxExportBatchSize {
+				bsp.exportSpans()
+			}
+		default:
+			close(bsp.queue)
 		}
 	}
-	bsp.exportSpans()
 }
 
 func (bsp *BatchSpanProcessor) enqueue(sd *export.SpanData) {
@@ -226,17 +233,19 @@ func (bsp *BatchSpanProcessor) enqueue(sd *export.SpanData) {
 		panic(x)
 	}()
 
+	select {
+	case <-bsp.stopCh:
+		return
+	default:
+	}
+
 	if bsp.o.BlockOnQueueFull {
-		select {
-		case bsp.queue <- sd:
-		case <-bsp.stopCh:
-		}
+		bsp.queue <- sd
 		return
 	}
 
 	select {
 	case bsp.queue <- sd:
-	case <-bsp.stopCh:
 	default:
 		atomic.AddUint32(&bsp.dropped, 1)
 	}

sdk/trace/batch_span_processor_test.go

@@ -117,7 +117,6 @@ func TestNewBatchSpanProcessorWithOptions(t *testing.T) {
 				sdktrace.WithBatchTimeout(schDelay),
 				sdktrace.WithMaxQueueSize(200),
 				sdktrace.WithMaxExportBatchSize(20),
-				sdktrace.WithBlocking(),
 			},
 			wantNumSpans:   205,
 			wantBatchCount: 11,
@@ -139,7 +138,6 @@ func TestNewBatchSpanProcessorWithOptions(t *testing.T) {
 			o: []sdktrace.BatchSpanProcessorOption{
 				sdktrace.WithBatchTimeout(schDelay),
 				sdktrace.WithMaxExportBatchSize(200),
-				sdktrace.WithBlocking(),
 			},
 			wantNumSpans:   2000,
 			wantBatchCount: 10,
@@ -162,18 +160,26 @@ func TestNewBatchSpanProcessorWithOptions(t *testing.T) {
 
 			tp.UnregisterSpanProcessor(ssp)
 
-			// TODO(https://github.com/open-telemetry/opentelemetry-go/issues/741)
-			// Restore some sort of test here.
-			_ = option.wantNumSpans
-			_ = option.wantBatchCount
-			_ = te.len()           // gotNumOfSpans
-			_ = te.getBatchCount() // gotBatchCount
+			gotNumOfSpans := te.len()
+			if option.wantNumSpans != gotNumOfSpans {
+				t.Errorf("number of exported span: got %+v, want %+v\n",
+					gotNumOfSpans, option.wantNumSpans)
+			}
+
+			gotBatchCount := te.getBatchCount()
+			if gotBatchCount < option.wantBatchCount {
+				t.Errorf("number batches: got %+v, want >= %+v\n",
+					gotBatchCount, option.wantBatchCount)
+				t.Errorf("Batches %v\n", te.sizes)
+			}
 		})
 	}
 }
 
 func createAndRegisterBatchSP(t *testing.T, option testOption, te *testBatchExporter) *sdktrace.BatchSpanProcessor {
-	ssp, err := sdktrace.NewBatchSpanProcessor(te, option.o...)
+	// Always use blocking queue to avoid flaky tests.
+	options := append(option.o, sdktrace.WithBlocking())
+	ssp, err := sdktrace.NewBatchSpanProcessor(te, options...)
 	if ssp == nil {
 		t.Errorf("%s: Error creating new instance of BatchSpanProcessor, error: %v\n", option.name, err)
 	}