From 29b9da5fb1f1fa528bacb12aebd83b60c2f65116 Mon Sep 17 00:00:00 2001
From: Andrew Kent <andrew.kent@datadoghq.com>
Date: Fri, 24 Aug 2018 10:07:22 -0700
Subject: [PATCH 1/2] Add getRootSpan() to MutableSpan

---
 .../datadog/trace/api/interceptor/MutableSpan.java |  2 ++
 .../src/main/java/datadog/opentracing/DDSpan.java  |  5 +++++
 .../groovy/datadog/opentracing/DDSpanTest.groovy   | 14 ++++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/dd-trace-api/src/main/java/datadog/trace/api/interceptor/MutableSpan.java b/dd-trace-api/src/main/java/datadog/trace/api/interceptor/MutableSpan.java
index 458e89208f..3bce89d3f9 100644
--- a/dd-trace-api/src/main/java/datadog/trace/api/interceptor/MutableSpan.java
+++ b/dd-trace-api/src/main/java/datadog/trace/api/interceptor/MutableSpan.java
@@ -41,4 +41,6 @@ public interface MutableSpan {
   Boolean isError();
 
   MutableSpan setError(boolean value);
+
+  MutableSpan getRootSpan();
 }
diff --git a/dd-trace-ot/src/main/java/datadog/opentracing/DDSpan.java b/dd-trace-ot/src/main/java/datadog/opentracing/DDSpan.java
index 34b08e4930..e523b4ce7a 100644
--- a/dd-trace-ot/src/main/java/datadog/opentracing/DDSpan.java
+++ b/dd-trace-ot/src/main/java/datadog/opentracing/DDSpan.java
@@ -125,6 +125,11 @@ public class DDSpan implements Span, MutableSpan {
     return this;
   }
 
+  @Override
+  public MutableSpan getRootSpan() {
+    return context().getTrace().getRootSpan();
+  }
+
   public void setErrorMeta(final Throwable error) {
     setError(true);
 
diff --git a/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanTest.groovy b/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanTest.groovy
index d228cfbee2..9abd211321 100644
--- a/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanTest.groovy
+++ b/dd-trace-ot/src/test/groovy/datadog/opentracing/DDSpanTest.groovy
@@ -183,4 +183,18 @@ class DDSpanTest extends Specification {
     child2.getMetrics().get(DDSpanContext.PRIORITY_SAMPLING_KEY) == null
     child2.getMetrics().get(DDSpanContext.SAMPLE_RATE_KEY) == null
   }
+
+  def "getRootSpan returns the root span"() {
+    setup:
+    def root = tracer.buildSpan("root").start()
+    def child = tracer.buildSpan("child").asChildOf(root).start()
+
+    expect:
+    root.getRootSpan() == root
+    child.getRootSpan() == root
+
+    cleanup:
+    child.finish()
+    root.finish()
+  }
 }

From bc105af06f214ebde3378d628b462cd932697da1 Mon Sep 17 00:00:00 2001
From: Andrew Kent <andrew.kent@datadoghq.com>
Date: Mon, 27 Aug 2018 11:33:21 -0700
Subject: [PATCH 2/2] Doc PendingTrace's root span.

---
 .../main/java/datadog/opentracing/PendingTrace.java    | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/dd-trace-ot/src/main/java/datadog/opentracing/PendingTrace.java b/dd-trace-ot/src/main/java/datadog/opentracing/PendingTrace.java
index 1ef8c7d770..f4c56319ad 100644
--- a/dd-trace-ot/src/main/java/datadog/opentracing/PendingTrace.java
+++ b/dd-trace-ot/src/main/java/datadog/opentracing/PendingTrace.java
@@ -40,6 +40,16 @@ public class PendingTrace extends ConcurrentLinkedDeque<DDSpan> {
       Collections.newSetFromMap(new ConcurrentHashMap<WeakReference<?>, Boolean>());
 
   private final AtomicInteger pendingReferenceCount = new AtomicInteger(0);
+  /**
+   * During a trace there are cases where the root span must be accessed (e.g. priority sampling and
+   * trace-search tags).
+   *
+   * <p>Use a weak ref because we still need to handle buggy cases where the root span is not
+   * correctly closed (see SpanCleaner).
+   *
+   * <p>The root span will be available in non-buggy cases because it has either finished and
+   * strongly ref'd in this queue or is unfinished and ref'd in a ContinuableScope.
+   */
   private final AtomicReference<WeakReference<DDSpan>> rootSpan = new AtomicReference<>();
 
   /** Ensure a trace is never written multiple times */