Initial implementation of a no-op active Span.

opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java

@@ -30,7 +30,7 @@
 import io.opentracing.Span;
 import io.opentracing.SpanContext;
 import io.opentracing.Tracer;
-import io.opentracing.noop.NoopScopeManager;
+import io.opentracing.noop.NoopSpanContext;
 import io.opentracing.propagation.Binary;
 import io.opentracing.propagation.Format;
 import io.opentracing.propagation.TextMap;
@@ -268,8 +268,7 @@ public <C> SpanContext extract(Format<C> format, C carrier) {
 
     @Override
     public Span activeSpan() {
-        Scope scope = this.scopeManager.active();
-        return scope == null ? null : scope.span();
+        return this.scopeManager.active().span();
     }
 
     @Override
@@ -304,6 +303,9 @@ public final class SpanBuilder implements Tracer.SpanBuilder {
 
         @Override
         public SpanBuilder asChildOf(SpanContext parent) {
+            if (parent == NoopSpanContext.INSTANCE) {
+                return  this;
+            }
             return addReference(References.CHILD_OF, parent);
         }
 
@@ -375,7 +377,7 @@ public MockSpan startManual() {
                 this.startMicros = MockSpan.nowMicros();
             }
             SpanContext activeSpanContext = activeSpanContext();
-            if(references.isEmpty() && !ignoringActiveSpan && activeSpanContext != null) {
+            if(references.isEmpty() && !ignoringActiveSpan && activeSpanContext != NoopSpanContext.INSTANCE) {
                 references.add(new MockSpan.Reference((MockSpan.MockContext) activeSpanContext, References.CHILD_OF));
             }
             return new MockSpan(MockTracer.this, operationName, startMicros, initialTags, references);

opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java

@@ -30,6 +30,7 @@
 import io.opentracing.Span;
 import io.opentracing.SpanContext;
 import io.opentracing.Tracer;
+import io.opentracing.noop.NoopSpan;
 import io.opentracing.propagation.Binary;
 import io.opentracing.propagation.BinaryAdapters;
 import io.opentracing.propagation.Format;
@@ -250,21 +251,21 @@ public void testBinaryPropagatorExtractError() {
     @Test
     public void testActiveSpan() {
         MockTracer mockTracer = new MockTracer();
-        Assert.assertNull(mockTracer.activeSpan());
+        Assert.assertEquals(NoopSpan.INSTANCE, mockTracer.activeSpan());
 
         Span span = mockTracer.buildSpan("foo").start();
         try (Scope scope = mockTracer.activateSpan(span)) {
             Assert.assertEquals(mockTracer.scopeManager().activeSpan(), mockTracer.activeSpan());
         }
 
-        Assert.assertNull(mockTracer.activeSpan());
+        Assert.assertEquals(NoopSpan.INSTANCE, mockTracer.activeSpan());
         Assert.assertTrue(mockTracer.finishedSpans().isEmpty());
     }
 
     @Test
     public void testActiveSpanFinish() {
         MockTracer mockTracer = new MockTracer();
-        Assert.assertNull(mockTracer.activeSpan());
+        Assert.assertEquals(NoopSpan.INSTANCE, mockTracer.activeSpan());
 
         Scope scope = null;
         try {
@@ -274,7 +275,7 @@ public void testActiveSpanFinish() {
             scope.close();
         }
 
-        Assert.assertNull(mockTracer.activeSpan());
+        Assert.assertEquals(NoopSpan.INSTANCE, mockTracer.activeSpan());
         Assert.assertFalse(mockTracer.finishedSpans().isEmpty());
     }
 

opentracing-noop/src/main/java/io/opentracing/noop/NoopScope.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2016-2018 The OpenTracing Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package io.opentracing.noop;
+
+import io.opentracing.Scope;
+import io.opentracing.Span;
+
+public interface NoopScope extends Scope {
+    NoopScope INSTANCE = new NoopScopeImpl();
+}
+
+class NoopScopeImpl implements NoopScope {
+    @Override
+    public void close() {}
+
+    @Override
+    public Span span() {
+        return NoopSpan.INSTANCE;
+    }
+}

opentracing-noop/src/main/java/io/opentracing/noop/NoopScopeManager.java

@@ -19,10 +19,6 @@
 
 public interface NoopScopeManager extends ScopeManager {
     NoopScopeManager INSTANCE = new NoopScopeManagerImpl();
-
-    interface NoopScope extends Scope {
-        NoopScope INSTANCE = new NoopScopeManagerImpl.NoopScopeImpl();
-    }
 }
 
 /**
@@ -48,14 +44,4 @@ public Scope active() {
     public Span activeSpan() {
         return NoopSpan.INSTANCE;
     }
-
-    static class NoopScopeImpl implements NoopScopeManager.NoopScope {
-        @Override
-        public void close() {}
-
-        @Override
-        public Span span() {
-            return NoopSpan.INSTANCE;
-        }
-    }
 }

opentracing-noop/src/main/java/io/opentracing/noop/NoopSpan.java

@@ -26,7 +26,7 @@ public interface NoopSpan extends Span {
 final class NoopSpanImpl implements NoopSpan {
 
     @Override
-    public SpanContext context() { return NoopSpanContextImpl.INSTANCE; }
+    public SpanContext context() { return NoopSpanContext.INSTANCE; }
 
     @Override
     public void finish() {}

opentracing-noop/src/main/java/io/opentracing/noop/NoopSpanBuilder.java

@@ -70,7 +70,7 @@ public Tracer.SpanBuilder withStartTimestamp(long microseconds) {
 
     @Override
     public Scope startActive(boolean finishOnClose) {
-        return NoopScopeManager.NoopScope.INSTANCE;
+        return NoopScope.INSTANCE;
     }
 
     @Override

opentracing-noop/src/main/java/io/opentracing/noop/NoopSpanContext.java

@@ -20,10 +20,10 @@
 
 
 public interface NoopSpanContext extends SpanContext {
+    static final NoopSpanContextImpl INSTANCE = new NoopSpanContextImpl();
 }
 
 final class NoopSpanContextImpl implements NoopSpanContext {
-    static final NoopSpanContextImpl INSTANCE = new NoopSpanContextImpl();
 
     @Override
     public String toTraceId() {

opentracing-noop/src/main/java/io/opentracing/noop/NoopTracer.java

@@ -38,7 +38,7 @@ public Span activeSpan() {
 
     @Override
     public Scope activateSpan(Span span) {
-        return NoopScopeManager.NoopScope.INSTANCE;
+        return NoopScope.INSTANCE;
     }
 
     @Override

opentracing-util/src/main/java/io/opentracing/util/ThreadLocalScopeManager.java

@@ -16,6 +16,8 @@
 import io.opentracing.Scope;
 import io.opentracing.ScopeManager;
 import io.opentracing.Span;
+import io.opentracing.noop.NoopScope;
+import io.opentracing.noop.NoopSpan;
 
 /**
  * A simple {@link ScopeManager} implementation built on top of Java's thread-local storage primitive.
@@ -37,12 +39,12 @@ public Scope activate(Span span) {
 
     @Override
     public Scope active() {
-        return tlsScope.get();
+        Scope scope = tlsScope.get();
+        return scope == null ? NoopScope.INSTANCE : scope;
     }
 
     @Override
     public Span activeSpan() {
-        Scope scope = tlsScope.get();
-        return scope == null ? null : scope.span();
+        return active().span();
     }
 }

opentracing-util/src/test/java/io/opentracing/util/ThreadLocalScopeManagerTest.java

@@ -15,6 +15,8 @@
 
 import io.opentracing.Scope;
 import io.opentracing.Span;
+import io.opentracing.noop.NoopScope;
+import io.opentracing.noop.NoopSpan;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -35,13 +37,13 @@ public void before() throws Exception {
     @Test
     public void missingActiveScope() throws Exception {
         Scope missingScope = source.active();
-        assertNull(missingScope);
+        assertEquals(NoopScope.INSTANCE, missingScope);
     }
 
     @Test
     public void missingActiveSpan() throws Exception {
         Span missingSpan = source.activeSpan();
-        assertNull(missingSpan);
+        assertEquals(NoopSpan.INSTANCE, missingSpan);
     }
 
     @Test
@@ -65,10 +67,10 @@ public void defaultActivate() throws Exception {
 
         // And now Scope/Span are gone:
         Scope missingScope = source.active();
-        assertNull(missingScope);
+        assertEquals(NoopScope.INSTANCE, missingScope);
 
         Span missingSpan = source.activeSpan();
-        assertNull(missingSpan);
+        assertEquals(NoopSpan.INSTANCE, missingSpan);
     }
 
     @Test
@@ -89,8 +91,8 @@ public void finishSpanClose() throws Exception {
         verify(span, times(1)).finish();
 
         // Verify Scope/Span are gone.
-        assertNull(source.active());
-        assertNull(source.activeSpan());
+        assertEquals(NoopScope.INSTANCE, source.active());
+        assertEquals(NoopSpan.INSTANCE, source.activeSpan());
     }
 
     @Test
@@ -111,7 +113,7 @@ public void dontFinishSpanNoClose() throws Exception {
         verify(span, never()).finish();
 
         // Verify Scope/Span are gone.
-        assertNull(source.active());
-        assertNull(source.activeSpan());
+        assertEquals(NoopScope.INSTANCE, source.active());
+        assertEquals(NoopSpan.INSTANCE, source.activeSpan());
     }
 }

opentracing-util/src/test/java/io/opentracing/util/ThreadLocalScopeTest.java

@@ -22,6 +22,7 @@
 
 import io.opentracing.Scope;
 import io.opentracing.Span;
+import io.opentracing.noop.NoopScope;
 import org.junit.Before;
 import org.junit.Test;
 
@@ -64,7 +65,7 @@ public void implicitSpanStack() throws Exception {
 
         // And now nothing is active.
         Scope missingSpan = scopeManager.active();
-        assertNull(missingSpan);
+        assertEquals(NoopScope.INSTANCE, missingSpan);
     }
 
     @Test