update with new rabit api

src/tree/param.h

@@ -205,8 +205,8 @@ struct GradStats {
     this->Add(b.sum_grad, b.sum_hess);
   }
   /*! \brief same as add, reduce is used in All Reduce */
-  inline void Reduce(const GradStats &b) {
-    this->Add(b);
+  inline static void Reduce(GradStats &a, const GradStats &b) {
+    a.Add(b);
   }
   /*! \brief set current value to a - b */
   inline void SetSubstract(const GradStats &a, const GradStats &b) {
@@ -285,8 +285,8 @@ struct CVGradStats : public GradStats {
     }
   }
   /*! \brief same as add, reduce is used in All Reduce */
-  inline void Reduce(const CVGradStats &b) {
-    this->Add(b);
+  inline static void Reduce(CVGradStats &a, const CVGradStats &b) {
+    a.Add(b);
   }
   /*! \brief set current value to a - b */
   inline void SetSubstract(const CVGradStats &a, const CVGradStats &b) {
@@ -368,8 +368,8 @@ struct SplitEntry{
     }
   }
   /*! \brief same as update, used by AllReduce*/
-  inline void Reduce(const SplitEntry &e) {
-    this->Update(e);
+  inline static void Reduce(SplitEntry &dst, const SplitEntry &src) {
+    dst.Update(src);
   }
   /*!\return feature index to split on */
   inline unsigned split_index(void) const {

src/tree/updater_distcol-inl.hpp

@@ -155,7 +155,7 @@ class DistColMaker : public ColMaker<TStats> {
    private:
     utils::BitMap bitmap;
     std::vector<int> boolmap;
-    rabit::Reducer<SplitEntry> reducer;
+    rabit::Reducer<SplitEntry, SplitEntry::Reduce> reducer;
   };
   // we directly introduce pruner here
   TreePruner pruner;

src/tree/updater_histmaker-inl.hpp

@@ -117,7 +117,7 @@ class HistMaker: public BaseMaker {
   // workspace of thread
   ThreadWSpace wspace;
   // reducer for histogram
-  rabit::Reducer<TStats> histred;
+  rabit::Reducer<TStats, TStats::Reduce> histred;
   // set of working features
   std::vector<bst_uint> fwork_set;
   // update function implementation

src/tree/updater_refresh-inl.hpp

@@ -147,7 +147,7 @@ class TreeRefresher: public IUpdater {
   // training parameter
   TrainParam param;
   // reducer
-  rabit::Reducer<TStats> reducer;  
+  rabit::Reducer<TStats, TStats::Reduce> reducer;  
 };
 
 }  // namespace tree