Add new extract method.

skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/TraceSegment.java

@@ -87,22 +87,40 @@ public class TraceSegment implements ISerializable<SegmentMessage> {
 
     /**
      * Establish the link between this segment and its parents.
+     * When {@param primaryOnly} is true;
      * The first time, you {@link #ref(TraceSegmentRef)} to parent, it is affirmed as {@link #primaryRef}.
      * And others are affirmed as {@link #refs}.
      *
      * @param refSegment {@link TraceSegmentRef}
+     * @param primaryOnly if true, set {@param refSegment} to {@link #primaryRef} only.
      */
-    public void ref(TraceSegmentRef refSegment) {
-        if (primaryRef == null) {
-            primaryRef = refSegment;
-        } else {
-            if (refs == null) {
-                refs = new LinkedList<TraceSegmentRef>();
+    public void ref(TraceSegmentRef refSegment, boolean primaryOnly) {
+        if(primaryOnly){
+            if (primaryRef == null) {
+                primaryRef = refSegment;
+            }
+        }else {
+            if (primaryRef == null) {
+                primaryRef = refSegment;
+            } else {
+                if (refs == null) {
+                    refs = new LinkedList<TraceSegmentRef>();
+                }
+                refs.add(refSegment);
             }
-            refs.add(refSegment);
         }
     }
 
+    /**
+     * Set to {@link #primaryRef} only,
+     * based on {@link #ref(TraceSegmentRef, boolean)}
+     *
+     * @param refSegment {@link TraceSegmentRef}
+     */
+    public void ref(TraceSegmentRef refSegment){
+        ref(refSegment, true);
+    }
+
     /**
      * After {@link Span} is finished, as be controller by "skywalking-api" module,
      * notify the {@link TraceSegment} to archive it.

skywalking-commons/skywalking-trace/src/test/java/com/a/eye/skywalking/trace/TraceSegmentTestCase.java

@@ -24,17 +24,17 @@ public class TraceSegmentTestCase {
         TraceSegmentRef ref1 = new TraceSegmentRef();
         ref1.setTraceSegmentId("parent_trace_0");
         ref1.setSpanId(1);
-        segment.ref(ref1);
+        segment.ref(ref1, false);
 
         TraceSegmentRef ref2 = new TraceSegmentRef();
         ref2.setTraceSegmentId("parent_trace_1");
         ref2.setSpanId(5);
-        segment.ref(ref2);
+        segment.ref(ref2, false);
 
         TraceSegmentRef ref3 = new TraceSegmentRef();
         ref3.setTraceSegmentId("parent_trace_1");
         ref3.setSpanId(5);
-        segment.ref(ref3);
+        segment.ref(ref3, false);
 
         Assert.assertEquals(ref1, segment.getPrimaryRef());
         Assert.assertEquals(ref2, segment.getRefs().get(0));
@@ -75,21 +75,21 @@ public class TraceSegmentTestCase {
         ref1.setSpanId(1);
         ref1.setApplicationCode("REMOTE_APP");
         ref1.setPeerHost("10.2.3.16:8080");
-        segment.ref(ref1);
+        segment.ref(ref1, false);
 
         TraceSegmentRef ref2 = new TraceSegmentRef();
         ref2.setTraceSegmentId("parent_trace_1");
         ref2.setSpanId(5);
         ref2.setApplicationCode("REMOTE_APP");
         ref2.setPeerHost("10.2.3.16:8080");
-        segment.ref(ref2);
+        segment.ref(ref2, false);
 
         TraceSegmentRef ref3 = new TraceSegmentRef();
         ref3.setTraceSegmentId("parent_trace_1");
         ref3.setSpanId(5);
         ref3.setApplicationCode("REMOTE_APP");
         ref3.setPeerHost("10.2.3.16:8080");
-        segment.ref(ref3);
+        segment.ref(ref3, false);
 
         Span span1 = new Span(1, "/serviceA");
         Tags.SPAN_LAYER.asHttp(span1);

skywalking-sniffer/skywalking-api/src/main/java/com/a/eye/skywalking/api/context/TracerContext.java

@@ -135,12 +135,30 @@ public final class TracerContext {
      * ContextCarrier#deserialize(String)} called.
      */
     public void extract(ContextCarrier carrier) {
+        if(carrier.isValid()) {
+            this.segment.ref(getRef(carrier));
+        }
+    }
+
+    /**
+     * Ref this {@link ContextCarrier} to this {@link TraceSegment}, and support multi-extract for supporting batch process, like MQ.
+     *
+     * @param carrier holds the snapshot, if get this {@link ContextCarrier} from remote, make sure {@link
+     * ContextCarrier#deserialize(String)} called.
+     */
+    public void multiExtract(ContextCarrier carrier){
+        if(carrier.isValid()) {
+            this.segment.ref(getRef(carrier), false);
+        }
+    }
+
+    private TraceSegmentRef getRef(ContextCarrier carrier){
         TraceSegmentRef ref = new TraceSegmentRef();
         ref.setTraceSegmentId(carrier.getTraceSegmentId());
         ref.setSpanId(carrier.getSpanId());
         ref.setApplicationCode(carrier.getApplicationCode());
         ref.setPeerHost(carrier.getPeerHost());
-        this.segment.ref(ref);
+        return ref;
     }
 
     /**