add distributed checking

include/rabit/c_api.h

@@ -46,6 +46,9 @@ RABIT_DLL int RabitGetRank();
 /*! \brief get total number of process */
 RABIT_DLL int RabitGetWorldSize();
 
+/*! \brief get rank of current process */
+RABIT_DLL int RabitIsDistributed();
+
 /*!
  * \brief print the msg to the tracker,
  *    this function can be used to communicate the information of the progress to

src/c_api.cc

@@ -178,6 +178,10 @@ int RabitGetWorldSize() {
   return rabit::GetWorldSize();
 }
 
+int RabitIsDistributed() {
+  return rabit::IsDistributed();
+}
+
 void RabitTrackerPrint(const char *msg) {
   std::string m(msg);
   rabit::TrackerPrint(m);