Make Tracer extends Closable. (#329)

* Make Tracer extends Closable.

opentracing-api/src/main/java/io/opentracing/Tracer.java

@@ -13,13 +13,15 @@
  */
 package io.opentracing;
 
+import java.io.Closeable;
+
 import io.opentracing.propagation.Format;
 import io.opentracing.tag.Tag;
 
 /**
  * Tracer is a simple, thin interface for Span creation and propagation across arbitrary transports.
  */
-public interface Tracer {
+public interface Tracer extends Closeable {
 
     /**
      * @return the current {@link ScopeManager}, which may be a noop but may not be null.
@@ -117,6 +119,19 @@ public interface Tracer {
      */
     <C> SpanContext extract(Format<C> format, C carrier);
 
+    /**
+     * Closes the Tracer, and tries to flush the in-memory collection to the configured persistance store.
+     *
+     * <p>
+     * The close method should be considered idempotent; closing an already closed Tracer should not raise an error.
+     * Spans that are created or finished after a Tracer has been closed may or may not be flushed.
+     * Calling the close method should be considered a synchronous operation. Observe this call may block for
+     * a relatively long period of time, depending on the internal shutdown.
+     * <p>
+     * For stateless tracers, this can be a no-op.
+     */
+    @Override
+    void close();
 
     interface SpanBuilder {
 

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

@@ -53,6 +53,7 @@ public class MockTracer implements Tracer {
     private final List<MockSpan> finishedSpans = new ArrayList<>();
     private final Propagator propagator;
     private final ScopeManager scopeManager;
+    private boolean isClosed;
 
     public MockTracer() {
         this(new ThreadLocalScopeManager(), Propagator.TEXT_MAP);
@@ -280,7 +281,16 @@ public Scope activateSpan(Span span) {
         return this.scopeManager.activate(span);
     }
 
+    @Override
+    public synchronized void close() {
+        this.isClosed = true;
+        this.finishedSpans.clear();
+    }
+
     synchronized void appendFinishedSpan(MockSpan mockSpan) {
+        if (isClosed)
+            return;
+
         this.finishedSpans.add(mockSpan);
         this.onSpanFinished(mockSpan);
     }

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

@@ -399,4 +399,16 @@ public void testChildOfWithNullParentDoesNotThrowException() {
         Span span = tracer.buildSpan("foo").asChildOf(parent).start();
         span.finish();
     }
+
+    @Test
+    public void testClose() {
+        MockTracer mockTracer = new MockTracer();
+        mockTracer.buildSpan("foo").start().finish();
+
+        mockTracer.close();
+        assertEquals(0, mockTracer.finishedSpans().size());
+
+        mockTracer.buildSpan("foo").start().finish();
+        assertEquals(0, mockTracer.finishedSpans().size());
+    }
 }

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

@@ -50,6 +50,9 @@ public <C> void inject(SpanContext spanContext, Format<C> format, C carrier) {}
     @Override
     public <C> SpanContext extract(Format<C> format, C carrier) { return NoopSpanContextImpl.INSTANCE; }
 
+    @Override
+    public void close() {}
+
     @Override
     public String toString() { return NoopTracer.class.getSimpleName(); }
 }

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

@@ -214,6 +214,11 @@ public Scope activateSpan(Span span) {
         return tracer.activateSpan(span);
     }
 
+    @Override
+    public void close() {
+        tracer.close();
+    }
+
     @Override
     public String toString() {
         return GlobalTracer.class.getSimpleName() + '{' + tracer + '}';

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

@@ -45,6 +45,7 @@
 import static org.junit.Assert.fail;
 import static org.mockito.Matchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 
@@ -225,6 +226,16 @@ public void testDelegation_extract() {
         verifyNoMoreInteractions(mockTracer, mockFormat, mockCarrier);
     }
 
+    @Test
+    public void testDelegation_close() {
+        Tracer mockTracer = mock(Tracer.class);
+        GlobalTracer.register(mockTracer);
+        GlobalTracer.get().close();
+
+        verify(mockTracer, times(1)).close();
+        verifyNoMoreInteractions(mockTracer);
+    }
+
     @Test
     public void concurrencyTest() throws InterruptedException, ExecutionException {
         final int threadCount = 10;