add sync module

src/tree/updater_basemaker-inl.hpp

@@ -8,7 +8,7 @@
 #include <vector>
 #include <algorithm>
 #include <limits>
-#include <rabit.h>
+#include "../sync/sync.h"
 #include "../utils/random.h"
 #include "../utils/quantile.h"
 

src/tree/updater_distcol-inl.hpp

@@ -6,7 +6,7 @@
  *        and construct a tree
  * \author Tianqi Chen
  */
-#include <rabit.h>
+#include "../sync/sync.h"
 #include "../utils/bitmap.h"
 #include "../utils/io.h"
 #include "./updater_colmaker-inl.hpp"

src/tree/updater_histmaker-inl.hpp

@@ -7,7 +7,7 @@
  */
 #include <vector>
 #include <algorithm>
-#include <rabit.h>
+#include "../sync/sync.h"
 #include "../utils/quantile.h"
 #include "../utils/group_data.h"
 #include "./updater_basemaker-inl.hpp"

src/tree/updater_refresh-inl.hpp

@@ -7,7 +7,7 @@
  */
 #include <vector>
 #include <limits>
-#include <rabit.h>
+#include "../sync/sync.h"
 #include "./param.h"
 #include "./updater.h"
 #include "../utils/omp.h"

src/tree/updater_sync-inl.hpp

@@ -7,7 +7,7 @@
  */
 #include <vector>
 #include <limits>
-#include <rabit.h>
+#include "../sync/sync.h"
 #include "./updater.h"
 
 namespace xgboost {