redefine distributed means

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);
 /*!

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;
   /*!

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();

src/allreduce_base.h

@@ -63,6 +63,10 @@ class AllreduceBase : public IEngine {
     if (world_size == -1) return 1;
     return world_size;
   }
+  /*! \brief whether is distributed or not */
+  virtual bool IsDistributed(void) const {
+    return tracker_uri == "NULL";
+  }
   /*! \brief get rank */
   virtual std::string GetHost(void) const {
     return host_uri;

src/engine_empty.cc

@@ -56,6 +56,10 @@ class EmptyEngine : public IEngine {
   virtual int GetWorldSize(void) const {
     return 1;
   }
+  /*! \brief whether it is distributed */
+  virtual bool IsDistributed(void) const {
+    return false;
+  }
   /*! \brief get the host name of current node */
   virtual std::string GetHost(void) const {
     return std::string("");

src/engine_mpi.cc

@@ -59,6 +59,10 @@ class MPIEngine : public IEngine {
   virtual int GetWorldSize(void) const {
     return MPI::COMM_WORLD.Get_size();
   }
+  /*! \brief whether it is distributed */
+  virtual bool IsDistributed(void) const {
+    return true;
+  }
   /*! \brief get the host name of current node */
   virtual std::string GetHost(void) const {
     int len;