compatibility issue with openmp

Makefile

@@ -1,6 +1,6 @@
 export CC  = gcc
 export CXX = g++
-export CFLAGS = -Wall -O3 -msse2 -fopenmp
+export CFLAGS = -Wall -O3 -msse2  -Wno-unknown-pragmas
 
 # specify tensor path
 BIN = xgboost

booster/tree/xgboost_col_treemaker.hpp

@@ -7,9 +7,9 @@
  * \author Tianqi Chen: tianqi.tchen@gmail.com 
  */
 // use openmp
-#include <omp.h>
 #include <vector>
 #include "xgboost_tree_model.h"
+#include "../../utils/xgboost_omp.h"
 #include "../../utils/xgboost_random.h"
 
 namespace xgboost{

booster/xgboost_gbmbase.h

@@ -1,9 +1,9 @@
 #ifndef XGBOOST_GBMBASE_H
 #define XGBOOST_GBMBASE_H
 
-#include <omp.h>
 #include <cstring>
 #include "xgboost.h"
+#include "../utils/xgboost_omp.h"
 #include "../utils/xgboost_config.h"
 /*!
  * \file xgboost_gbmbase.h

regression/xgboost_reg.h

@@ -8,9 +8,9 @@
 #include <cmath>
 #include <cstdlib>
 #include <cstring>
-#include <omp.h>
 #include "xgboost_reg_data.h"
 #include "xgboost_reg_eval.h"
+#include "../utils/xgboost_omp.h"
 #include "../booster/xgboost_gbmbase.h"
 #include "../utils/xgboost_utils.h"
 #include "../utils/xgboost_stream.h"

regression/xgboost_reg_eval.h

@@ -5,11 +5,12 @@
 * \brief evaluation metrics for regression and classification
 * \author Kailong Chen: chenkl198812@gmail.com, Tianqi Chen: tianqi.tchen@gmail.com
 */
-#include <omp.h>
+
 #include <cmath>
 #include <vector>
 #include <algorithm>
 #include "../utils/xgboost_utils.h"
+#include "../utils/xgboost_omp.h"
 
 namespace xgboost{
     namespace regression{

utils/xgboost_omp.h

@@ -0,0 +1,18 @@
+#ifndef XGBOOST_OMP_H
+#define XGBOOST_OMP_H
+/*!
+ * \file xgboost_omp.h
+ * \brief header to handle OpenMP compatibility issues
+ * 
+ * \author Tianqi Chen: tianqi.tchen@gmail.com
+ */
+
+#if defined(_OPENMP)
+#include <omp.h>
+#else
+#warning "OpenMP is not available, compile to single thread code"
+inline int omp_get_thread_num() { return 0; }
+inline int omp_get_num_threads() { return 1; }
+inline void omp_set_num_threads( int nthread ) {}
+#endif
+#endif