Make DDSpan, NoopSpan, and BlackHoleSpan each SelfScopedContexts to further reduce allocations

Author: mcculls

components/context/src/main/java/datadog/context/SelfScopedContext.java

@@ -1,7 +1,7 @@
 package datadog.context;
 
 /** Context that acts as its own unattached scope. */
-interface SelfScopedContext extends Context, ContextScope {
+public interface SelfScopedContext extends Context, ContextScope {
   @Override
   default ContextScope asScope() {
     return this; // acts as no-op scope, avoiding allocation

dd-trace-core/src/main/java/datadog/trace/core/DDSpan.java

@@ -9,6 +9,7 @@
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 
+import datadog.context.SelfScopedContext;
 import datadog.trace.api.Config;
 import datadog.trace.api.DDSpanId;
 import datadog.trace.api.DDTags;
@@ -50,7 +51,8 @@
  * <p>Spans are created by the {@link CoreTracer#buildSpan}. This implementation adds some features
  * according to the DD agent.
  */
-public class DDSpan implements AgentSpan, CoreSpan<DDSpan>, AttachableWrapper {
+@SuppressWarnings("resource")
+public class DDSpan implements AgentSpan, CoreSpan<DDSpan>, AttachableWrapper, SelfScopedContext {
   private static final Logger log = LoggerFactory.getLogger(DDSpan.class);
 
   static DDSpan create(

dd-trace-core/src/main/java/datadog/trace/core/PendingTrace.java

@@ -210,6 +210,7 @@ private void trackRunningTrace(final DDSpan span) {
   }
 
   Integer evaluateSamplingPriority() {
+    @SuppressWarnings("resource")
     DDSpan span = spans.peek();
     if (span == null) {
       return null;

internal-api/src/main/java/datadog/trace/bootstrap/instrumentation/api/NoopSpan.java

@@ -1,5 +1,6 @@
 package datadog.trace.bootstrap.instrumentation.api;
 
+import datadog.context.SelfScopedContext;
 import datadog.trace.api.DDSpanId;
 import datadog.trace.api.DDTraceId;
 import datadog.trace.api.TagMap;
@@ -8,7 +9,7 @@
 import datadog.trace.api.gateway.RequestContext;
 import datadog.trace.api.sampling.PrioritySampling;
 
-class NoopSpan extends ImmutableSpan implements AgentSpan {
+class NoopSpan extends ImmutableSpan implements AgentSpan, SelfScopedContext {
   static final NoopSpan INSTANCE = new NoopSpan();
 
   NoopSpan() {}