feat(profiling): capture span execution thread at finish time in DDSpanContext

Author: kaahos

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

@@ -160,6 +160,11 @@ private void finishAndAddToTrace(final long durationNano) {
         wrapper.onSpanFinished();
       }
       this.metrics.onSpanFinished();
+      // Capture the execution thread while still on the span's own finishing thread.
+      // CoreTracer.write() is called later from the event loop; the info captured here is the
+      // authoritative source for SpanNode thread attribution (see SpanExecutionThreadEvent).
+      context.captureExecutionThread(
+          Thread.currentThread().getId(), Thread.currentThread().getName());
       TraceCollector.PublishState publishState = context.getTraceCollector().onPublish(this);
       log.debug("Finished span ({}): {}", publishState, this);
     } else {

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

@@ -160,6 +160,8 @@ public class DDSpanContext
   private final boolean injectBaggageAsTags;
   private volatile int encodedOperationName;
   private volatile int encodedResourceName;
+  private volatile long executionThreadId = 0;
+  private volatile String executionThreadName = "";
 
   /**
    * Metastruct keys are associated to the current span, they will not propagate to the children
@@ -387,6 +389,25 @@ public int getEncodedResourceName() {
     return encodedResourceName;
   }
 
+  public ProfilingContextIntegration getProfilingContextIntegration() {
+    return profilingContextIntegration;
+  }
+
+  void captureExecutionThread(long threadId, String threadName) {
+    this.executionThreadId = threadId;
+    this.executionThreadName = threadName;
+  }
+
+  @Override
+  public long getExecutionThreadId() {
+    return executionThreadId;
+  }
+
+  @Override
+  public String getExecutionThreadName() {
+    return executionThreadName;
+  }
+
   public String getServiceName() {
     return serviceName;
   }