[exporterqueue] Default Batcher that reads from the queue, batches an…

…d exports (open-telemetry#11546)

#### Description

This PR follows
open-telemetry#11540 and
implements support for item-count based batching for queue batcher.

Limitation: This PR supports merging request but not splitting request.
In other words, it support specifying a minimum request size but not a
maximum request size.

Design doc:

https://docs.google.com/document/d/1y5jt7bQ6HWt04MntF8CjUwMBBeNiJs2gV4uUZfJjAsE/edit?usp=sharing

#### Link to tracking issue

open-telemetry#8122
open-telemetry#10368

exporter/internal/queue/batcher.go

@@ -33,12 +33,23 @@ type BaseBatcher struct {
 }
 
 func NewBatcher(batchCfg exporterbatcher.Config, queue Queue[internal.Request], maxWorkers int) (Batcher, error) {
-	if batchCfg.Enabled {
+	if !batchCfg.Enabled {
+		return &DisabledBatcher{
+			BaseBatcher{
+				batchCfg:   batchCfg,
+				queue:      queue,
+				maxWorkers: maxWorkers,
+				stopWG:     sync.WaitGroup{},
+			},
+		}, nil
+	}
+
+	if batchCfg.MaxSizeConfig.MaxSizeItems != 0 {
 		return nil, errors.ErrUnsupported
 	}
 
-	return &DisabledBatcher{
-		BaseBatcher{
+	return &DefaultBatcher{
+		BaseBatcher: BaseBatcher{
 			batchCfg:   batchCfg,
 			queue:      queue,
 			maxWorkers: maxWorkers,

exporter/internal/queue/default_batcher.go

@@ -0,0 +1,122 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package queue // import "go.opentelemetry.io/collector/exporter/internal/queue"
+
+import (
+	"context"
+	"math"
+	"sync"
+	"time"
+
+	"go.opentelemetry.io/collector/component"
+)
+
+// DefaultBatcher continuously reads from the queue and flushes asynchronously if size limit is met or on timeout.
+type DefaultBatcher struct {
+	BaseBatcher
+	currentBatchMu sync.Mutex
+	currentBatch   *batch
+	timer          *time.Timer
+	shutdownCh     chan bool
+}
+
+func (qb *DefaultBatcher) resetTimer() {
+	if qb.batchCfg.FlushTimeout != 0 {
+		qb.timer.Reset(qb.batchCfg.FlushTimeout)
+	}
+}
+
+// startReadingFlushingGoroutine starts a goroutine that reads and then flushes.
+func (qb *DefaultBatcher) startReadingFlushingGoroutine() {
+
+	qb.stopWG.Add(1)
+	go func() {
+		defer qb.stopWG.Done()
+		for {
+			// Read() blocks until the queue is non-empty or until the queue is stopped.
+			idx, ctx, req, ok := qb.queue.Read(context.Background())
+			if !ok {
+				qb.shutdownCh <- true
+				return
+			}
+
+			qb.currentBatchMu.Lock()
+			if qb.currentBatch == nil || qb.currentBatch.req == nil {
+				qb.resetTimer()
+				qb.currentBatch = &batch{
+					req:     req,
+					ctx:     ctx,
+					idxList: []uint64{idx}}
+			} else {
+				mergedReq, mergeErr := qb.currentBatch.req.Merge(qb.currentBatch.ctx, req)
+				if mergeErr != nil {
+					qb.queue.OnProcessingFinished(idx, mergeErr)
+					qb.currentBatchMu.Unlock()
+					continue
+				}
+				qb.currentBatch = &batch{
+					req:     mergedReq,
+					ctx:     qb.currentBatch.ctx,
+					idxList: append(qb.currentBatch.idxList, idx)}
+			}
+
+			if qb.currentBatch.req.ItemsCount() > qb.batchCfg.MinSizeItems {
+				batchToFlush := *qb.currentBatch
+				qb.currentBatch = nil
+				qb.currentBatchMu.Unlock()
+
+				// flushAsync() blocks until successfully started a goroutine for flushing.
+				qb.flushAsync(batchToFlush)
+				qb.resetTimer()
+			} else {
+				qb.currentBatchMu.Unlock()
+			}
+		}
+	}()
+}
+
+// startTimeBasedFlushingGoroutine starts a goroutine that flushes on timeout.
+func (qb *DefaultBatcher) startTimeBasedFlushingGoroutine() {
+	qb.stopWG.Add(1)
+	go func() {
+		defer qb.stopWG.Done()
+		for {
+			select {
+			case <-qb.shutdownCh:
+				return
+			case <-qb.timer.C:
+				qb.currentBatchMu.Lock()
+				if qb.currentBatch == nil || qb.currentBatch.req == nil {
+					qb.currentBatchMu.Unlock()
+					continue
+				}
+				batchToFlush := *qb.currentBatch
+				qb.currentBatch = nil
+				qb.currentBatchMu.Unlock()
+
+				// flushAsync() blocks until successfully started a goroutine for flushing.
+				qb.flushAsync(batchToFlush)
+				qb.resetTimer()
+			}
+		}
+	}()
+}
+
+// Start starts the goroutine that reads from the queue and flushes asynchronously.
+func (qb *DefaultBatcher) Start(_ context.Context, _ component.Host) error {
+	qb.startWorkerPool()
+	qb.shutdownCh = make(chan bool, 1)
+
+	if qb.batchCfg.FlushTimeout == 0 {
+		qb.timer = time.NewTimer(math.MaxInt)
+		qb.timer.Stop()
+	} else {
+		qb.timer = time.NewTimer(qb.batchCfg.FlushTimeout)
+	}
+
+	qb.startReadingFlushingGoroutine()
+	qb.startTimeBasedFlushingGoroutine()
+
+	return nil
+}

exporter/internal/queue/default_batcher_test.go

@@ -0,0 +1,217 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package queue
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/collector/component/componenttest"
+	"go.opentelemetry.io/collector/exporter/exporterbatcher"
+	"go.opentelemetry.io/collector/exporter/internal"
+)
+
+func TestDefaultBatcher_MinThresholdZero_TimeoutDisabled(t *testing.T) {
+	tests := []struct {
+		name       string
+		maxWorkers int
+	}{
+		{
+			name:       "infinate_workers",
+			maxWorkers: 0,
+		},
+		{
+			name:       "one_worker",
+			maxWorkers: 1,
+		},
+		{
+			name:       "three_workers",
+			maxWorkers: 3,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := exporterbatcher.NewDefaultConfig()
+			cfg.Enabled = true
+			cfg.FlushTimeout = 0
+			cfg.MinSizeConfig = exporterbatcher.MinSizeConfig{
+				MinSizeItems: 0,
+			}
+
+			q := NewBoundedMemoryQueue[internal.Request](
+				MemoryQueueSettings[internal.Request]{
+					Sizer:    &RequestSizer[internal.Request]{},
+					Capacity: 10,
+				})
+
+			ba, err := NewBatcher(cfg, q, tt.maxWorkers)
+			require.NoError(t, err)
+
+			require.NoError(t, q.Start(context.Background(), componenttest.NewNopHost()))
+			require.NoError(t, ba.Start(context.Background(), componenttest.NewNopHost()))
+			t.Cleanup(func() {
+				require.NoError(t, q.Shutdown(context.Background()))
+				require.NoError(t, ba.Shutdown(context.Background()))
+			})
+
+			sink := newFakeRequestSink()
+
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 8, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 8, exportErr: errors.New("transient error"), sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 17, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 13, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 35, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 2, sink: sink}))
+			assert.Eventually(t, func() bool {
+				return sink.requestsCount.Load() == 5 && sink.itemsCount.Load() == 75
+			}, 30*time.Millisecond, 10*time.Millisecond)
+		})
+	}
+}
+
+func TestDefaultBatcher_TimeoutDisabled(t *testing.T) {
+	tests := []struct {
+		name       string
+		maxWorkers int
+	}{
+		{
+			name:       "infinate_workers",
+			maxWorkers: 0,
+		},
+		{
+			name:       "one_worker",
+			maxWorkers: 1,
+		},
+		{
+			name:       "three_workers",
+			maxWorkers: 3,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := exporterbatcher.NewDefaultConfig()
+			cfg.Enabled = true
+			cfg.FlushTimeout = 0
+			cfg.MinSizeConfig = exporterbatcher.MinSizeConfig{
+				MinSizeItems: 10,
+			}
+
+			q := NewBoundedMemoryQueue[internal.Request](
+				MemoryQueueSettings[internal.Request]{
+					Sizer:    &RequestSizer[internal.Request]{},
+					Capacity: 10,
+				})
+
+			ba, err := NewBatcher(cfg, q, tt.maxWorkers)
+			require.NoError(t, err)
+
+			require.NoError(t, q.Start(context.Background(), componenttest.NewNopHost()))
+			require.NoError(t, ba.Start(context.Background(), componenttest.NewNopHost()))
+			t.Cleanup(func() {
+				require.NoError(t, q.Shutdown(context.Background()))
+				require.NoError(t, ba.Shutdown(context.Background()))
+			})
+
+			sink := newFakeRequestSink()
+
+			// These two requests will be dropped because of export error.
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 8, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 8, exportErr: errors.New("transient error"), sink: sink}))
+
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 7, sink: sink}))
+
+			// This request will be dropped because of merge error
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 8, mergeErr: errors.New("transient error"), sink: sink}))
+
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 13, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 35, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 2, sink: sink}))
+			assert.Eventually(t, func() bool {
+				return sink.requestsCount.Load() == 2 && sink.itemsCount.Load() == 55
+			}, 30*time.Millisecond, 10*time.Millisecond)
+		})
+	}
+}
+
+func TestDefaultBatcher_WithTimeout(t *testing.T) {
+	tests := []struct {
+		name       string
+		maxWorkers int
+	}{
+		{
+			name:       "infinate_workers",
+			maxWorkers: 0,
+		},
+		{
+			name:       "one_worker",
+			maxWorkers: 1,
+		},
+		{
+			name:       "three_workers",
+			maxWorkers: 3,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := exporterbatcher.NewDefaultConfig()
+			cfg.Enabled = true
+			cfg.FlushTimeout = 50 * time.Millisecond
+			cfg.MinSizeConfig = exporterbatcher.MinSizeConfig{
+				MinSizeItems: 100,
+			}
+
+			q := NewBoundedMemoryQueue[internal.Request](
+				MemoryQueueSettings[internal.Request]{
+					Sizer:    &RequestSizer[internal.Request]{},
+					Capacity: 10,
+				})
+
+			ba, err := NewBatcher(cfg, q, tt.maxWorkers)
+			require.NoError(t, err)
+
+			require.NoError(t, q.Start(context.Background(), componenttest.NewNopHost()))
+			require.NoError(t, ba.Start(context.Background(), componenttest.NewNopHost()))
+			t.Cleanup(func() {
+				require.NoError(t, q.Shutdown(context.Background()))
+				require.NoError(t, ba.Shutdown(context.Background()))
+			})
+
+			sink := newFakeRequestSink()
+
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 8, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 17, sink: sink}))
+
+			// This request will be dropped because of merge error
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 8, mergeErr: errors.New("transient error"), sink: sink}))
+
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 13, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 35, sink: sink}))
+			require.NoError(t, q.Offer(context.Background(), &fakeRequest{items: 2, sink: sink}))
+			assert.Eventually(t, func() bool {
+				return sink.requestsCount.Load() == 1 && sink.itemsCount.Load() == 75
+			}, 100*time.Millisecond, 10*time.Millisecond)
+		})
+	}
+}
+
+func TestDisabledBatcher_SplitNotImplemented(t *testing.T) {
+	cfg := exporterbatcher.NewDefaultConfig()
+	cfg.Enabled = true
+	maxWorkers := 0
+	cfg.MaxSizeConfig.MaxSizeItems = 1
+
+	q := NewBoundedMemoryQueue[internal.Request](
+		MemoryQueueSettings[internal.Request]{
+			Sizer:    &RequestSizer[internal.Request]{},
+			Capacity: 10,
+		})
+
+	_, err := NewBatcher(cfg, q, maxWorkers)
+	require.Error(t, err)
+}

exporter/internal/queue/disabled_batcher_test.go

@@ -70,18 +70,3 @@ func TestDisabledBatcher_Basic(t *testing.T) {
 		})
 	}
 }
-
-func TestDisabledBatcher_BatchingNotImplemented(t *testing.T) {
-	cfg := exporterbatcher.NewDefaultConfig()
-	cfg.Enabled = true
-	maxWorkers := 0
-
-	q := NewBoundedMemoryQueue[internal.Request](
-		MemoryQueueSettings[internal.Request]{
-			Sizer:    &RequestSizer[internal.Request]{},
-			Capacity: 10,
-		})
-
-	_, err := NewBatcher(cfg, q, maxWorkers)
-	require.Error(t, err)
-}