Default implementation for empty BatchProcessor

Ensure an empty BatchProcessor does not panic when any method is called.

Initialize the empty BatchProcessor to use the default/envar setup if
not created with NewBatchProcessor.

Part of #5063

sdk/log/batch.go

@@ -100,7 +100,12 @@ type BatchProcessor struct {
 //
 // All of the exporter's methods are called synchronously.
 func NewBatchProcessor(exporter Exporter, opts ...BatchProcessorOption) *BatchProcessor {
-	cfg := newBatchConfig(opts)
+	b := new(BatchProcessor)
+	b.init(exporter, newBatchConfig(opts))
+	return b
+}
+
+func (b *BatchProcessor) init(exporter Exporter, cfg batchConfig) {
 	if exporter == nil {
 		// Do not panic on nil export.
 		exporter = defaultNoopExporter
@@ -113,17 +118,13 @@ func NewBatchProcessor(exporter Exporter, opts ...BatchProcessorOption) *BatchPr
 	// appropriately on export.
 	exporter = newChunkExporter(exporter, cfg.expMaxBatchSize.Value)
 
-	b := &BatchProcessor{
-		// TODO: explore making the size of this configurable.
-		exporter: newBufferExporter(exporter, 1),
-
-		q:           newQueue(cfg.maxQSize.Value),
-		batchSize:   cfg.expMaxBatchSize.Value,
-		pollTrigger: make(chan struct{}, 1),
-		pollKill:    make(chan struct{}),
-	}
+	// TODO (#5238): explore making the size of this configurable.
+	b.exporter = newBufferExporter(exporter, 1)
+	b.q = newQueue(cfg.maxQSize.Value)
+	b.batchSize = cfg.expMaxBatchSize.Value
+	b.pollTrigger = make(chan struct{}, 1)
+	b.pollKill = make(chan struct{})
 	b.pollDone = b.poll(cfg.expInterval.Value)
-	return b
 }
 
 // poll spawns a goroutine to handle interval polling and batch exporting. The
@@ -173,6 +174,9 @@ func (b *BatchProcessor) OnEmit(_ context.Context, r Record) error {
 	if b.stopped.Load() {
 		return nil
 	}
+	if b.q == nil {
+		b.init(nil, newBatchConfig(nil))
+	}
 	if n := b.q.Enqueue(r); n >= b.batchSize {
 		select {
 		case b.pollTrigger <- struct{}{}:
@@ -196,6 +200,11 @@ func (b *BatchProcessor) Shutdown(ctx context.Context) error {
 		return nil
 	}
 
+	if b.q == nil {
+		// Nothing to stop.
+		return nil
+	}
+
 	// Stop the poll goroutine.
 	close(b.pollKill)
 	select {
@@ -223,6 +232,11 @@ func (b *BatchProcessor) ForceFlush(ctx context.Context) error {
 		return nil
 	}
 
+	if b.q == nil {
+		// Nothing to flush.
+		return nil
+	}
+
 	buf := make([]Record, b.q.cap)
 	notFlushed := func() bool {
 		var flushed bool

sdk/log/batch_test.go

@@ -18,6 +18,47 @@ import (
 	"go.opentelemetry.io/otel/log"
 )
 
+func TestEmptyBatchConfig(t *testing.T) {
+	assert.NotPanics(t, func() {
+		var bp BatchProcessor
+		ctx := context.Background()
+		var record Record
+		assert.NoError(t, bp.OnEmit(ctx, record), "OnEmit")
+
+		assert.NotNil(t, bp.exporter, "Exporter")
+		if assert.NotNil(t, bp.q, "queue") {
+			assert.Equal(t, dfltMaxQSize, bp.q.cap, "queue capacity")
+		}
+		assert.Equal(t, dfltExpMaxBatchSize, bp.batchSize, "batch size")
+		assert.NotNil(t, bp.pollTrigger, "poll trigger chan")
+		assert.NotNil(t, bp.pollKill, "poll kill chan")
+		assert.NotNil(t, bp.pollDone, "poll done chan")
+
+		assert.True(t, bp.Enabled(ctx, record), "Enabled")
+		assert.NoError(t, bp.ForceFlush(ctx), "ForceFlush")
+		assert.NoError(t, bp.Shutdown(ctx), "Shutdown")
+	}, "init via OnEmit")
+
+	assert.NotPanics(t, func() {
+		var bp BatchProcessor
+		ctx := context.Background()
+		var record Record
+		assert.True(t, bp.Enabled(ctx, record), "Enabled")
+	}, "Enabled")
+
+	assert.NotPanics(t, func() {
+		var bp BatchProcessor
+		ctx := context.Background()
+		assert.NoError(t, bp.ForceFlush(ctx), "ForceFlush")
+	}, "ForceFlush")
+
+	assert.NotPanics(t, func() {
+		var bp BatchProcessor
+		ctx := context.Background()
+		assert.NoError(t, bp.Shutdown(ctx), "Shutdown")
+	}, "Shutdown")
+}
+
 func TestNewBatchConfig(t *testing.T) {
 	otel.SetErrorHandler(otel.ErrorHandlerFunc(func(err error) {
 		t.Log(err)