feat(core): Extract and refactor span and scope implementations from tracer

Add dedicated noop methods for span, span context and scope
Remove unused eligibleForDropping method
Improve Javadoc

Author: PerfectSlayer

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/instrumentation/java/concurrent/ConcurrentState.java

@@ -4,7 +4,6 @@
 
 import datadog.trace.bootstrap.ContextStore;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -32,7 +31,7 @@ private ConcurrentState() {}
   public static <K> ConcurrentState captureScope(
       ContextStore<K, ConcurrentState> contextStore, K key, AgentScope scope) {
     if (scope != null && scope.isAsyncPropagating()) {
-      if (scope.span() instanceof AgentTracer.NoopAgentSpan) {
+      if (!scope.span().isValid()) {
         return null;
       }
       final ConcurrentState state = contextStore.putIfAbsent(key, FACTORY);

dd-java-agent/instrumentation/akka-concurrent/src/main/java/datadog/trace/instrumentation/akka/concurrent/AkkaActorCellInstrumentation.java

@@ -4,6 +4,7 @@
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activateSpan;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activeScope;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activeSpan;
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.noopSpan;
 import static java.util.Collections.singletonMap;
 import static net.bytebuddy.matcher.ElementMatchers.isMethod;
 
@@ -13,7 +14,6 @@
 import datadog.trace.agent.tooling.InstrumenterModule;
 import datadog.trace.bootstrap.InstrumentationContext;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.bootstrap.instrumentation.java.concurrent.AdviceUtils;
 import datadog.trace.bootstrap.instrumentation.java.concurrent.State;
 import java.util.Map;
@@ -72,11 +72,11 @@ public static AgentScope enter(
         return null;
       }
       // If there is a noop span in the active scope, we can clean all the way to this scope
-      if (activeSpan() instanceof AgentTracer.NoopAgentSpan) {
+      if (activeSpan() == noopSpan()) {
         return activeScope;
       }
       // Create an active scope with a noop span, and clean all the way to the previous scope
-      localScope = activateSpan(AgentTracer.NoopAgentSpan.INSTANCE, false);
+      localScope = activateSpan(noopSpan(), false);
       return activeScope;
     }
 

dd-java-agent/instrumentation/akka-concurrent/src/main/java/datadog/trace/instrumentation/akka/concurrent/AkkaMailboxInstrumentation.java

@@ -4,6 +4,7 @@
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activateSpan;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activeScope;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activeSpan;
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.noopSpan;
 import static java.util.Collections.singletonList;
 import static net.bytebuddy.matcher.ElementMatchers.isMethod;
 
@@ -12,7 +13,6 @@
 import datadog.trace.agent.tooling.Instrumenter;
 import datadog.trace.agent.tooling.InstrumenterModule;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.bootstrap.instrumentation.java.concurrent.ExcludeFilter;
 import java.util.Collection;
 import java.util.EnumMap;
@@ -69,11 +69,11 @@ public static AgentScope enter() {
         return null;
       }
       // If there is a noop span in the active scope, we can clean all the way to this scope
-      if (activeSpan() instanceof AgentTracer.NoopAgentSpan) {
+      if (activeSpan() == noopSpan()) {
         return activeScope;
       }
       // Create an active scope with a noop span, and clean all the way to the previous scope
-      activateSpan(AgentTracer.NoopAgentSpan.INSTANCE, false);
+      activateSpan(noopSpan(), false);
       return activeScope;
     }
 

dd-java-agent/instrumentation/aws-java-sdk-1.11.0/src/main/java/datadog/trace/instrumentation/aws/v0/AWSHttpClientInstrumentation.java

@@ -12,7 +12,6 @@
 import datadog.trace.agent.tooling.Instrumenter;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import net.bytebuddy.asm.Advice;
 
 /**
@@ -50,7 +49,7 @@ public static void methodExit(
       // check name in case TracingRequestHandler failed to activate the span
       if (scope != null
           && (AwsNameCache.spanName(request).equals(scope.span().getSpanName())
-              || scope.span() instanceof AgentTracer.NoopAgentSpan)) {
+              || !scope.span().isValid())) {
         scope.close();
       }
 

dd-java-agent/instrumentation/aws-java-sdk-1.11.0/src/main/java/datadog/trace/instrumentation/aws/v0/RequestExecutorInstrumentation.java

@@ -10,7 +10,6 @@
 import datadog.trace.agent.tooling.Instrumenter;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import net.bytebuddy.asm.Advice;
 
 /**
@@ -47,7 +46,7 @@ public static void methodExit(
       // check name in case TracingRequestHandler failed to activate the span
       if (scope != null
           && (AwsNameCache.spanName(request).equals(scope.span().getSpanName())
-              || scope.span() instanceof AgentTracer.NoopAgentSpan)) {
+              || !scope.span().isValid())) {
         scope.close();
       }
 

dd-java-agent/instrumentation/aws-java-sdk-2.2/src/main/java/datadog/trace/instrumentation/aws/v2/AwsHttpClientInstrumentation.java

@@ -15,7 +15,6 @@
 import datadog.trace.agent.tooling.Instrumenter;
 import datadog.trace.agent.tooling.InstrumenterModule;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import net.bytebuddy.asm.Advice;
 import net.bytebuddy.description.type.TypeDescription;
 import net.bytebuddy.matcher.ElementMatcher;
@@ -76,7 +75,7 @@ public static AgentScope methodEnter(
       final AgentScope scope = activeScope();
       // check name in case TracingExecutionInterceptor failed to activate the span
       if (scope != null
-          && (scope.span() instanceof AgentTracer.NoopAgentSpan
+          && ((!scope.span().isValid())
               || AwsSdkClientDecorator.DECORATE
                   .spanName(requestExecutionContext.executionAttributes())
                   .equals(scope.span().getSpanName()))) {

dd-java-agent/instrumentation/netty-4.0/src/main/java/datadog/trace/instrumentation/netty40/NettyChannelHandlerContextInstrumentation.java

@@ -5,6 +5,7 @@
 import static datadog.trace.agent.tooling.bytebuddy.matcher.NameMatchers.named;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activateSpan;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activeSpan;
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.noopScope;
 import static datadog.trace.instrumentation.netty40.AttributeKeys.SPAN_ATTRIBUTE_KEY;
 import static datadog.trace.instrumentation.netty40.NettyChannelPipelineInstrumentation.ADDITIONAL_INSTRUMENTATION_NAMES;
 import static datadog.trace.instrumentation.netty40.NettyChannelPipelineInstrumentation.INSTRUMENTATION_NAME;
@@ -16,7 +17,6 @@
 import datadog.trace.agent.tooling.InstrumenterModule;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.instrumentation.netty40.client.NettyHttpClientDecorator;
 import datadog.trace.instrumentation.netty40.server.NettyHttpServerDecorator;
 import io.netty.channel.ChannelHandlerContext;
@@ -72,7 +72,7 @@ public static AgentScope scopeSpan(@Advice.This final ChannelHandlerContext ctx)
       final AgentSpan channelSpan = ctx.channel().attr(SPAN_ATTRIBUTE_KEY).get();
       if (channelSpan == null || channelSpan == activeSpan()) {
         // don't modify the scope
-        return AgentTracer.NoopAgentScope.INSTANCE;
+        return noopScope();
       }
       return activateSpan(channelSpan);
     }

dd-java-agent/instrumentation/netty-4.1/src/main/java/datadog/trace/instrumentation/netty41/NettyChannelHandlerContextInstrumentation.java

@@ -5,6 +5,7 @@
 import static datadog.trace.agent.tooling.bytebuddy.matcher.NameMatchers.named;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activateSpan;
 import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.activeSpan;
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.noopScope;
 import static datadog.trace.instrumentation.netty41.AttributeKeys.SPAN_ATTRIBUTE_KEY;
 import static datadog.trace.instrumentation.netty41.NettyChannelPipelineInstrumentation.ADDITIONAL_INSTRUMENTATION_NAMES;
 import static datadog.trace.instrumentation.netty41.NettyChannelPipelineInstrumentation.INSTRUMENTATION_NAME;
@@ -16,7 +17,6 @@
 import datadog.trace.agent.tooling.InstrumenterModule;
 import datadog.trace.bootstrap.instrumentation.api.AgentScope;
 import datadog.trace.bootstrap.instrumentation.api.AgentSpan;
-import datadog.trace.bootstrap.instrumentation.api.AgentTracer;
 import datadog.trace.instrumentation.netty41.client.NettyHttpClientDecorator;
 import datadog.trace.instrumentation.netty41.server.NettyHttpServerDecorator;
 import io.netty.channel.ChannelHandlerContext;
@@ -72,7 +72,7 @@ public static AgentScope scopeSpan(@Advice.This final ChannelHandlerContext ctx)
       final AgentSpan channelSpan = ctx.channel().attr(SPAN_ATTRIBUTE_KEY).get();
       if (channelSpan == null || channelSpan == activeSpan()) {
         // don't modify the scope
-        return AgentTracer.NoopAgentScope.INSTANCE;
+        return noopScope();
       }
       return activateSpan(channelSpan);
     }

dd-java-agent/instrumentation/okhttp-2/src/test/groovy/OkHttp2AsyncTest.groovy

@@ -7,6 +7,7 @@ import datadog.trace.bootstrap.instrumentation.api.AgentTracer
 import java.util.concurrent.CountDownLatch
 import java.util.concurrent.atomic.AtomicReference
 
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.noopSpan
 import static java.util.concurrent.TimeUnit.SECONDS
 
 abstract class OkHttp2AsyncTest extends OkHttp2Test {
@@ -52,7 +53,7 @@ abstract class OkHttp2AsyncTest extends OkHttp2Test {
   def "callbacks should carry context with error = #error" () {
 
     when:
-    def captured = AgentTracer.noopSpan()
+    def captured = noopSpan()
     try {
       TraceUtils.runUnderTrace("parent", {
         doRequest(method, url, ["Datadog-Meta-Lang": "java"], "", { captured = AgentTracer.activeSpan() })

dd-java-agent/instrumentation/okhttp-3/src/test/groovy/OkHttp3AsyncTest.groovy

@@ -13,6 +13,7 @@ import okhttp3.internal.http.HttpMethod
 import java.util.concurrent.CountDownLatch
 import java.util.concurrent.atomic.AtomicReference
 
+import static datadog.trace.bootstrap.instrumentation.api.AgentTracer.noopSpan
 import static java.util.concurrent.TimeUnit.SECONDS
 
 abstract class OkHttp3AsyncTest extends OkHttp3Test {
@@ -52,7 +53,7 @@ abstract class OkHttp3AsyncTest extends OkHttp3Test {
   def "callbacks should carry context with error = #error" () {
 
     when:
-    def captured = AgentTracer.noopSpan()
+    def captured = noopSpan()
     try {
       TraceUtils.runUnderTrace("parent", {
         doRequest(method, url, ["Datadog-Meta-Lang": "java"], "", { captured = AgentTracer.activeSpan() })