Hide implementation of MultiSpanExporter/Processor behind interface. (#2091)

* Hide implementation of MultiSpanExporter behind interface.

* spanprocessor too

* composite

* composite

* Optimize composites based on number of items.

* Spotless

* IntelliJ + spotless race condition

* Fix test

sdk-extensions/async-processor/src/test/java/io/opentelemetry/sdk/extension/trace/export/DisruptorAsyncSpanProcessorTest.java

@@ -10,7 +10,6 @@ import static org.assertj.core.api.Assertions.assertThat;
 import io.opentelemetry.context.Context;
 import io.opentelemetry.sdk.common.CompletableResultCode;
 import io.opentelemetry.sdk.common.export.ConfigBuilder;
-import io.opentelemetry.sdk.trace.MultiSpanProcessor;
 import io.opentelemetry.sdk.trace.ReadWriteSpan;
 import io.opentelemetry.sdk.trace.ReadableSpan;
 import io.opentelemetry.sdk.trace.SpanProcessor;
@@ -225,7 +224,7 @@ class DisruptorAsyncSpanProcessorTest {
     IncrementSpanProcessor incrementSpanProcessor2 = new IncrementSpanProcessor(REQUIRED, REQUIRED);
     DisruptorAsyncSpanProcessor disruptorAsyncSpanProcessor =
         DisruptorAsyncSpanProcessor.builder(
-                MultiSpanProcessor.create(
+                SpanProcessor.composite(
                     Arrays.asList(incrementSpanProcessor1, incrementSpanProcessor2)))
             .build();
     disruptorAsyncSpanProcessor.onStart(Context.root(), readWriteSpan);

sdk/all/src/jmh/java/io/opentelemetry/sdk/trace/export/MultiSpanExporterBenchmark.java

@@ -61,7 +61,7 @@ public class MultiSpanExporterBenchmark {
   public final void setup() {
     SpanExporter[] exporter = new SpanExporter[exporterCount];
     Arrays.fill(exporter, new NoopSpanExporter());
-    this.exporter = MultiSpanExporter.create(Arrays.asList(exporter));
+    this.exporter = SpanExporter.composite(Arrays.asList(exporter));
 
     TestSpanData[] spans = new TestSpanData[spanCount];
     for (int i = 0; i < spans.length; i++) {

sdk/tracing/src/main/java/io/opentelemetry/sdk/trace/MultiSpanProcessor.java

@@ -15,7 +15,10 @@ import java.util.concurrent.atomic.AtomicBoolean;
 /**
  * Implementation of the {@code SpanProcessor} that simply forwards all received events to a list of
  * {@code SpanProcessor}s.
+ *
+ * @deprecated Use {@link SpanProcessor#composite(SpanProcessor...)}
  */
+@Deprecated
 public final class MultiSpanProcessor implements SpanProcessor {
   private final List<SpanProcessor> spanProcessorsStart;
   private final List<SpanProcessor> spanProcessorsEnd;
@@ -28,7 +31,9 @@ public final class MultiSpanProcessor implements SpanProcessor {
    * @param spanProcessorList the {@code List} of {@code SpanProcessor}s.
    * @return a new {@code MultiSpanProcessor}.
    * @throws NullPointerException if the {@code spanProcessorList} is {@code null}.
+   * @deprecated Use {@link SpanProcessor#composite(SpanProcessor...)}
    */
+  @Deprecated
   public static SpanProcessor create(List<SpanProcessor> spanProcessorList) {
     return new MultiSpanProcessor(
         new ArrayList<>(Objects.requireNonNull(spanProcessorList, "spanProcessorList")));

sdk/tracing/src/main/java/io/opentelemetry/sdk/trace/SpanProcessor.java

@@ -8,12 +8,43 @@ package io.opentelemetry.sdk.trace;
 import io.opentelemetry.api.trace.Span;
 import io.opentelemetry.context.Context;
 import io.opentelemetry.sdk.common.CompletableResultCode;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 
 /**
  * SpanProcessor is the interface {@code TracerSdk} uses to allow synchronous hooks for when a
  * {@code Span} is started or when a {@code Span} is ended.
  */
 public interface SpanProcessor {
+
+  /**
+   * Returns a {@link SpanProcessor} which simply delegates all processing to the {@code processors}
+   * in order.
+   */
+  static SpanProcessor composite(SpanProcessor... processors) {
+    return composite(Arrays.asList(processors));
+  }
+
+  /**
+   * Returns a {@link SpanProcessor} which simply delegates all processing to the {@code processors}
+   * in order.
+   */
+  @SuppressWarnings("deprecation")
+  static SpanProcessor composite(Iterable<SpanProcessor> processors) {
+    List<SpanProcessor> processorsList = new ArrayList<>();
+    for (SpanProcessor processor : processors) {
+      processorsList.add(processor);
+    }
+    if (processorsList.isEmpty()) {
+      return NoopSpanProcessor.getInstance();
+    }
+    if (processorsList.size() == 1) {
+      return processorsList.get(0);
+    }
+    return MultiSpanProcessor.create(processorsList);
+  }
+
   /**
    * Called when a {@link io.opentelemetry.api.trace.Span} is started, if the {@link
    * Span#isRecording()} returns true.

sdk/tracing/src/main/java/io/opentelemetry/sdk/trace/TracerSharedState.java

@@ -82,7 +82,7 @@ final class TracerSharedState {
   void addSpanProcessor(SpanProcessor spanProcessor) {
     synchronized (lock) {
       registeredSpanProcessors.add(spanProcessor);
-      activeSpanProcessor = MultiSpanProcessor.create(registeredSpanProcessors);
+      activeSpanProcessor = SpanProcessor.composite(registeredSpanProcessors);
     }
   }
 

sdk/tracing/src/main/java/io/opentelemetry/sdk/trace/export/MultiSpanExporter.java

@@ -19,7 +19,10 @@ import java.util.logging.Logger;
  *
  * <p>Can be used to export to multiple backends using the same {@code SpanProcessor} like a {@code
  * SimpleSampledSpansProcessor} or a {@code BatchSampledSpansProcessor}.
+ *
+ * @deprecated Use {@link SpanExporter#composite(SpanExporter...)}
  */
+@Deprecated
 public final class MultiSpanExporter implements SpanExporter {
   private static final Logger logger = Logger.getLogger(MultiSpanExporter.class.getName());
 
@@ -30,9 +33,11 @@ public final class MultiSpanExporter implements SpanExporter {
    *
    * @param spanExporters the exporters spans should be sent to
    * @return the aggregate span exporter
+   * @deprecated Use {@link SpanExporter#composite(SpanExporter...)}
    */
+  @Deprecated
   public static SpanExporter create(List<SpanExporter> spanExporters) {
-    return new MultiSpanExporter(spanExporters);
+    return new MultiSpanExporter(spanExporters.toArray(new SpanExporter[0]));
   }
 
   @Override
@@ -94,7 +99,7 @@ public final class MultiSpanExporter implements SpanExporter {
     return CompletableResultCode.ofAll(results);
   }
 
-  private MultiSpanExporter(List<SpanExporter> spanExporters) {
-    this.spanExporters = spanExporters.toArray(new SpanExporter[0]);
+  private MultiSpanExporter(SpanExporter[] spanExporters) {
+    this.spanExporters = spanExporters;
   }
 }

sdk/tracing/src/main/java/io/opentelemetry/sdk/trace/export/NoopSpanExporter.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.trace.export;
+
+import io.opentelemetry.sdk.common.CompletableResultCode;
+import io.opentelemetry.sdk.trace.data.SpanData;
+import java.util.Collection;
+
+final class NoopSpanExporter implements SpanExporter {
+
+  private static final SpanExporter INSTANCE = new NoopSpanExporter();
+
+  static SpanExporter getInstance() {
+    return INSTANCE;
+  }
+
+  @Override
+  public CompletableResultCode export(Collection<SpanData> spans) {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode flush() {
+    return CompletableResultCode.ofSuccess();
+  }
+
+  @Override
+  public CompletableResultCode shutdown() {
+    return CompletableResultCode.ofSuccess();
+  }
+}

sdk/tracing/src/main/java/io/opentelemetry/sdk/trace/export/SpanExporter.java

@@ -8,7 +8,10 @@ package io.opentelemetry.sdk.trace.export;
 import io.opentelemetry.sdk.common.CompletableResultCode;
 import io.opentelemetry.sdk.trace.TracerSdkManagement;
 import io.opentelemetry.sdk.trace.data.SpanData;
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
+import java.util.List;
 
 /**
  * An interface that allows different tracing services to export recorded data for sampled spans in
@@ -19,6 +22,39 @@ import java.util.Collection;
  */
 public interface SpanExporter {
 
+  /**
+   * Returns a {@link SpanExporter} which simply delegates all exports to the {@code exporters} in
+   * order.
+   *
+   * <p>Can be used to export to multiple backends using the same {@code SpanProcessor} like a
+   * {@code SimpleSampledSpansProcessor} or a {@code BatchSampledSpansProcessor}.
+   */
+  static SpanExporter composite(SpanExporter... exporters) {
+    return composite(Arrays.asList(exporters));
+  }
+
+  /**
+   * Returns a {@link SpanExporter} which simply delegates all exports to the {@code exporters} in
+   * order.
+   *
+   * <p>Can be used to export to multiple backends using the same {@code SpanProcessor} like a
+   * {@code SimpleSampledSpansProcessor} or a {@code BatchSampledSpansProcessor}.
+   */
+  @SuppressWarnings("deprecation")
+  static SpanExporter composite(Iterable<SpanExporter> exporters) {
+    List<SpanExporter> exportersList = new ArrayList<>();
+    for (SpanExporter exporter : exporters) {
+      exportersList.add(exporter);
+    }
+    if (exportersList.isEmpty()) {
+      return NoopSpanExporter.getInstance();
+    }
+    if (exportersList.size() == 1) {
+      return exportersList.get(0);
+    }
+    return MultiSpanExporter.create(exportersList);
+  }
+
   /**
    * Called to export sampled {@code Span}s. Note that export operations can be performed
    * simultaneously depending on the type of span processor being used. However, the {@link

sdk/tracing/src/test/java/io/opentelemetry/sdk/trace/MultiSpanProcessorTest.java

@@ -10,7 +10,6 @@ import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.same;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.when;
 
 import io.opentelemetry.context.Context;
@@ -43,7 +42,7 @@ class MultiSpanProcessorTest {
 
   @Test
   void empty() {
-    SpanProcessor multiSpanProcessor = MultiSpanProcessor.create(Collections.emptyList());
+    SpanProcessor multiSpanProcessor = SpanProcessor.composite(Collections.emptyList());
     multiSpanProcessor.onStart(Context.root(), readWriteSpan);
     multiSpanProcessor.onEnd(readableSpan);
     multiSpanProcessor.shutdown();
@@ -52,50 +51,14 @@ class MultiSpanProcessorTest {
   @Test
   void oneSpanProcessor() {
     SpanProcessor multiSpanProcessor =
-        MultiSpanProcessor.create(Collections.singletonList(spanProcessor1));
-    multiSpanProcessor.onStart(Context.root(), readWriteSpan);
-    verify(spanProcessor1).onStart(same(Context.root()), same(readWriteSpan));
-
-    multiSpanProcessor.onEnd(readableSpan);
-    verify(spanProcessor1).onEnd(same(readableSpan));
-
-    multiSpanProcessor.forceFlush();
-    verify(spanProcessor1).forceFlush();
-
-    multiSpanProcessor.shutdown();
-    verify(spanProcessor1).shutdown();
-  }
-
-  @Test
-  void oneSpanProcessor_NoRequirements() {
-    when(spanProcessor1.isStartRequired()).thenReturn(false);
-    when(spanProcessor1.isEndRequired()).thenReturn(false);
-    SpanProcessor multiSpanProcessor =
-        MultiSpanProcessor.create(Collections.singletonList(spanProcessor1));
-
-    verify(spanProcessor1).isStartRequired();
-    verify(spanProcessor1).isEndRequired();
-
-    assertThat(multiSpanProcessor.isStartRequired()).isFalse();
-    assertThat(multiSpanProcessor.isEndRequired()).isFalse();
-
-    multiSpanProcessor.onStart(Context.root(), readWriteSpan);
-    verifyNoMoreInteractions(spanProcessor1);
-
-    multiSpanProcessor.onEnd(readableSpan);
-    verifyNoMoreInteractions(spanProcessor1);
-
-    multiSpanProcessor.forceFlush();
-    verify(spanProcessor1).forceFlush();
-
-    multiSpanProcessor.shutdown();
-    verify(spanProcessor1).shutdown();
+        SpanProcessor.composite(Collections.singletonList(spanProcessor1));
+    assertThat(multiSpanProcessor).isSameAs(spanProcessor1);
   }
 
   @Test
   void twoSpanProcessor() {
     SpanProcessor multiSpanProcessor =
-        MultiSpanProcessor.create(Arrays.asList(spanProcessor1, spanProcessor2));
+        SpanProcessor.composite(Arrays.asList(spanProcessor1, spanProcessor2));
     multiSpanProcessor.onStart(Context.root(), readWriteSpan);
     verify(spanProcessor1).onStart(same(Context.root()), same(readWriteSpan));
     verify(spanProcessor2).onStart(same(Context.root()), same(readWriteSpan));
@@ -118,7 +81,7 @@ class MultiSpanProcessorTest {
     when(spanProcessor1.isEndRequired()).thenReturn(false);
     when(spanProcessor2.isStartRequired()).thenReturn(false);
     SpanProcessor multiSpanProcessor =
-        MultiSpanProcessor.create(Arrays.asList(spanProcessor1, spanProcessor2));
+        SpanProcessor.composite(Arrays.asList(spanProcessor1, spanProcessor2));
 
     assertThat(multiSpanProcessor.isStartRequired()).isTrue();
     assertThat(multiSpanProcessor.isEndRequired()).isTrue();

sdk/tracing/src/test/java/io/opentelemetry/sdk/trace/export/BatchSpanProcessorTest.java

@@ -212,7 +212,7 @@ class BatchSpanProcessorTest {
         new WaitingSpanExporter(2, CompletableResultCode.ofSuccess());
     tracerSdkFactory.addSpanProcessor(
         BatchSpanProcessor.builder(
-                MultiSpanExporter.create(Arrays.asList(waitingSpanExporter, waitingSpanExporter2)))
+                SpanExporter.composite(Arrays.asList(waitingSpanExporter, waitingSpanExporter2)))
             .setScheduleDelayMillis(MAX_SCHEDULE_DELAY_MILLIS)
             .build());
 
@@ -231,7 +231,7 @@ class BatchSpanProcessorTest {
         new WaitingSpanExporter(maxQueuedSpans, CompletableResultCode.ofSuccess());
     BatchSpanProcessor batchSpanProcessor =
         BatchSpanProcessor.builder(
-                MultiSpanExporter.create(Arrays.asList(blockingSpanExporter, waitingSpanExporter)))
+                SpanExporter.composite(Arrays.asList(blockingSpanExporter, waitingSpanExporter)))
             .setScheduleDelayMillis(MAX_SCHEDULE_DELAY_MILLIS)
             .setMaxQueueSize(maxQueuedSpans)
             .setMaxExportBatchSize(maxQueuedSpans / 2)
@@ -296,7 +296,7 @@ class BatchSpanProcessorTest {
         .export(ArgumentMatchers.anyList());
     tracerSdkFactory.addSpanProcessor(
         BatchSpanProcessor.builder(
-                MultiSpanExporter.create(Arrays.asList(mockServiceHandler, waitingSpanExporter)))
+                SpanExporter.composite(Arrays.asList(mockServiceHandler, waitingSpanExporter)))
             .setScheduleDelayMillis(MAX_SCHEDULE_DELAY_MILLIS)
             .build());
     ReadableSpan span1 = createSampledEndedSpan(SPAN_NAME_1);

sdk/tracing/src/test/java/io/opentelemetry/sdk/trace/export/MultiSpanExporterTest.java

@@ -32,7 +32,7 @@ class MultiSpanExporterTest {
 
   @Test
   void empty() {
-    SpanExporter multiSpanExporter = MultiSpanExporter.create(Collections.emptyList());
+    SpanExporter multiSpanExporter = SpanExporter.composite(Collections.emptyList());
     multiSpanExporter.export(SPAN_LIST);
     multiSpanExporter.shutdown();
   }
@@ -40,7 +40,7 @@ class MultiSpanExporterTest {
   @Test
   void oneSpanExporter() {
     SpanExporter multiSpanExporter =
-        MultiSpanExporter.create(Collections.singletonList(spanExporter1));
+        SpanExporter.composite(Collections.singletonList(spanExporter1));
 
     when(spanExporter1.export(same(SPAN_LIST))).thenReturn(CompletableResultCode.ofSuccess());
     assertThat(multiSpanExporter.export(SPAN_LIST).isSuccess()).isTrue();
@@ -58,7 +58,7 @@ class MultiSpanExporterTest {
   @Test
   void twoSpanExporter() {
     SpanExporter multiSpanExporter =
-        MultiSpanExporter.create(Arrays.asList(spanExporter1, spanExporter2));
+        SpanExporter.composite(Arrays.asList(spanExporter1, spanExporter2));
 
     when(spanExporter1.export(same(SPAN_LIST))).thenReturn(CompletableResultCode.ofSuccess());
     when(spanExporter2.export(same(SPAN_LIST))).thenReturn(CompletableResultCode.ofSuccess());
@@ -82,7 +82,7 @@ class MultiSpanExporterTest {
   @Test
   void twoSpanExporter_OneReturnFailure() {
     SpanExporter multiSpanExporter =
-        MultiSpanExporter.create(Arrays.asList(spanExporter1, spanExporter2));
+        SpanExporter.composite(Arrays.asList(spanExporter1, spanExporter2));
 
     when(spanExporter1.export(same(SPAN_LIST))).thenReturn(CompletableResultCode.ofSuccess());
     when(spanExporter2.export(same(SPAN_LIST))).thenReturn(CompletableResultCode.ofFailure());
@@ -106,7 +106,7 @@ class MultiSpanExporterTest {
   @Test
   void twoSpanExporter_FirstThrows() {
     SpanExporter multiSpanExporter =
-        MultiSpanExporter.create(Arrays.asList(spanExporter1, spanExporter2));
+        SpanExporter.composite(Arrays.asList(spanExporter1, spanExporter2));
 
     Mockito.doThrow(new IllegalArgumentException("No export for you."))
         .when(spanExporter1)