added context-free endSubsegment to AWSXRay class (#229)

Author: willarmiros

aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/AWSXRay.java

@@ -105,7 +105,7 @@ public static Segment beginSegment(String name, TraceID traceId, String parentId
     }
 
     /**
-     * @deprecated Use {@code AWSXray.getGlobalRecorder().beginNoOpSegment() }.
+     * @deprecated Use {@code AWSXRay.getGlobalRecorder().beginNoOpSegment() }.
      */
     @Deprecated
     public static Segment beginDummySegment() {
@@ -124,6 +124,10 @@ public static void endSubsegment() {
         globalRecorder.endSubsegment();
     }
 
+    public static void endSubsegment(@Nullable Subsegment subsegment) {
+        globalRecorder.endSubsegment(subsegment);
+    }
+
     @Nullable
     public String currentEntityId() {
         return globalRecorder.currentEntityId();

aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/AWSXRayRecorder.java

@@ -562,12 +562,13 @@ public void endSegment() {
     }
 
     /**
-     * Ends the provided subsegment. This method doesn't touch context storage.
+     * Ends the provided subsegment. This method doesn't touch context storage and should be used when ending custom subsegments
+     * in asynchronous methods or other threads.
      *
      * @param subsegment
      *          the subsegment to close.
      */
-    public void endSubsegment(Subsegment subsegment) {
+    public void endSubsegment(@Nullable Subsegment subsegment) {
         if (subsegment == null) {
             logger.debug("No input subsegment to end. No-op.");
             return;