return values in Init and Finalize (#96)

* make inti function return values

* address the comments

include/rabit/c_api.h

@@ -32,14 +32,16 @@ typedef unsigned long rbt_ulong;  // NOLINT(*)
  *  from environment variables.
  * \param argc number of arguments in argv
  * \param argv the array of input arguments
+ * \return true if rabit is initialized successfully otherwise false
  */
-RABIT_DLL void RabitInit(int argc, char *argv[]);
+RABIT_DLL bool RabitInit(int argc, char *argv[]);
 
 /*!
  * \brief finalize the rabit engine,
  * call this function after you finished all jobs.
+ * \return true if rabit is initialized successfully otherwise false
  */
-RABIT_DLL void RabitFinalize(void);
+RABIT_DLL bool RabitFinalize(void);
 
 /*!
  * \brief get rank of current process

include/rabit/internal/engine.h

@@ -161,9 +161,9 @@ class IEngine {
 };
 
 /*! \brief initializes the engine module */
-void Init(int argc, char *argv[]);
+bool Init(int argc, char *argv[]);
 /*! \brief finalizes the engine module */
-void Finalize(void);
+bool Finalize(void);
 /*! \brief singleton method to get engine */
 IEngine *GetEngine(void);
 

include/rabit/internal/rabit-inl.h

@@ -103,12 +103,12 @@ inline void Reducer(const void *src_, void *dst_, int len, const MPI::Datatype &
 }  // namespace op
 
 // intialize the rabit engine
-inline void Init(int argc, char *argv[]) {
-  engine::Init(argc, argv);
+inline bool Init(int argc, char *argv[]) {
+  return engine::Init(argc, argv);
 }
 // finalize the rabit engine
-inline void Finalize(void) {
-  engine::Finalize();
+inline bool Finalize(void) {
+  return engine::Finalize();
 }
 // get the rank of current process
 inline int GetRank(void) {

include/rabit/rabit.h

@@ -73,12 +73,14 @@ struct BitOR;
  * \brief initializes rabit, call this once at the beginning of your program
  * \param argc number of arguments in argv
  * \param argv the array of input arguments
+ * \return true if initialized successfully, otherwise false
  */
-inline void Init(int argc, char *argv[]);
+inline bool Init(int argc, char *argv[]);
 /*!
  * \brief finalizes the rabit engine, call this function after you finished with all the jobs
+ * \return true if finalized successfully, otherwise false
  */
-inline void Finalize();
+inline bool Finalize();
 /*! \brief gets rank of the current process
  * \return rank number of worker*/
 inline int GetRank();