don't notify scope listeners if trace is eligible for dropping

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

@@ -304,6 +304,17 @@ public final DDSpan setResourceName(final CharSequence resourceName) {
     return this;
   }
 
+  @Override
+  public boolean eligibleForDropping() {
+    switch (context.getSamplingPriority()) {
+      case PrioritySampling.USER_DROP:
+      case PrioritySampling.SAMPLER_DROP:
+        return !context.getErrorFlag() & !forceKeep;
+      default:
+        return false;
+    }
+  }
+
   /**
    * Set the sampling priority of the root span of this span's trace
    *

dd-trace-core/src/main/java/datadog/trace/core/scopemanager/ContinuableScopeManager.java

@@ -178,7 +178,7 @@ private static final class ContinuableScope implements AgentScope {
     /** Flag to propagate this scope across async boundaries. */
     private boolean isAsyncPropagating;
 
-    private final byte source;
+    private byte flags;
 
     private short referenceCount = 1;
 
@@ -194,7 +194,7 @@ private static final class ContinuableScope implements AgentScope {
       this.span = span;
       this.scopeManager = scopeManager;
       this.continuation = continuation;
-      this.source = source;
+      this.flags = source;
     }
 
     @Override
@@ -210,7 +210,7 @@ public void close() {
 
         scopeManager.statsDClient.incrementCounter("scope.close.error");
 
-        if (source == ScopeSource.MANUAL.id()) {
+        if (source() == ScopeSource.MANUAL.id()) {
           scopeManager.statsDClient.incrementCounter("scope.user.close.error");
 
           if (scopeManager.strictMode) {
@@ -247,7 +247,7 @@ final void onProperClose() {
         }
       }
 
-      if (span instanceof NoopAgentSpan) {
+      if (!notifiedOnActivate()) {
         return;
       }
 
@@ -297,7 +297,7 @@ public void setAsyncPropagation(final boolean value) {
     @Override
     public ContinuableScopeManager.Continuation capture() {
       return isAsyncPropagating
-          ? new SingleContinuation(scopeManager, span, source).register()
+          ? new SingleContinuation(scopeManager, span, source()).register()
           : null;
     }
 
@@ -309,7 +309,7 @@ public ContinuableScopeManager.Continuation capture() {
     @Override
     public ContinuableScopeManager.Continuation captureConcurrent() {
       return isAsyncPropagating
-          ? new ConcurrentContinuation(scopeManager, span, source).register()
+          ? new ConcurrentContinuation(scopeManager, span, source()).register()
           : null;
     }
 
@@ -327,9 +327,10 @@ public void afterActivated() {
         }
       }
 
-      if (span instanceof NoopAgentSpan) {
+      if (span.eligibleForDropping()) {
         return;
       }
+      flags |= 0x80;
 
       for (final ExtendedScopeListener listener : scopeManager.extendedScopeListeners) {
         try {
@@ -339,6 +340,14 @@ public void afterActivated() {
         }
       }
     }
+
+    private byte source() {
+      return (byte) (flags & 0x7F);
+    }
+
+    private boolean notifiedOnActivate() {
+      return flags < 0;
+    }
   }
 
   /**

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

@@ -74,6 +74,8 @@ public interface AgentSpan extends MutableSpan {
   @Override
   AgentSpan setResourceName(final CharSequence resourceName);
 
+  boolean eligibleForDropping();
+
   interface Context {
     DDId getTraceId();
 

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

@@ -353,6 +353,11 @@ public AgentSpan setResourceName(final CharSequence resourceName) {
       return this;
     }
 
+    @Override
+    public boolean eligibleForDropping() {
+      return true;
+    }
+
     @Override
     public Integer getSamplingPriority() {
       return (int) PrioritySampling.UNSET;