Merge commit '4c060df2f17405dc26dc65a77e412d5c2a23525a'

Conflicts:
	subtree/rabit/tracker/rabit_yarn.py

subtree/rabit/include/rabit.h

@@ -65,9 +65,8 @@ inline int GetRank(void);
 /*! \brief gets total number of processes */
 inline int GetWorldSize(void);
 /*! \brief whether rabit env is in distributed mode */
-inline bool IsDistributed(void) {
-  return GetWorldSize() != 1;
-}
+inline bool IsDistributed(void);
+
 /*! \brief gets processor's name */
 inline std::string GetProcessorName(void);
 /*!

subtree/rabit/include/rabit/engine.h

@@ -145,6 +145,8 @@ class IEngine {
   virtual int GetRank(void) const = 0;
   /*! \brief gets total number of nodes */
   virtual int GetWorldSize(void) const = 0;
+  /*! \brief whether we run in distribted mode */
+  virtual bool IsDistributed(void) const = 0;
   /*! \brief gets the host name of the current node */
   virtual std::string GetHost(void) const = 0;
   /*!

subtree/rabit/include/rabit/rabit-inl.h

@@ -107,6 +107,10 @@ inline int GetRank(void) {
 inline int GetWorldSize(void) {
   return engine::GetEngine()->GetWorldSize();
 }
+// whether rabit is distributed
+inline bool IsDistributed(void) {
+  return engine::GetEngine()->IsDistributed();
+}
 // get the name of current processor
 inline std::string GetProcessorName(void) {
   return engine::GetEngine()->GetHost();