Revert C API change.

src/c_api/c_api.cc

@@ -11,8 +11,8 @@
 #include <string>
 #include <memory>
 
+
 #include "xgboost/data.h"
-#include "xgboost/host_device_vector.h"
 #include "xgboost/learner.h"
 #include "xgboost/c_api.h"
 #include "xgboost/logging.h"
@@ -146,7 +146,7 @@ struct XGBAPIThreadLocalEntry {
   /*! \brief result holder for returning string pointers */
   std::vector<const char *> ret_vec_charp;
   /*! \brief returning float vector. */
-  HostDeviceVector<bst_float> ret_vec_float;
+  std::vector<bst_float> ret_vec_float;
   /*! \brief temp variable of gradient pairs. */
   std::vector<GradientPair> tmp_gpair;
 };
@@ -553,22 +553,24 @@ XGB_DLL int XGBoosterPredict(BoosterHandle handle,
                              int32_t training,
                              xgboost::bst_ulong *len,
                              const bst_float **out_result) {
+  std::vector<bst_float>& preds =
+      XGBAPIThreadLocalStore::Get()->ret_vec_float;
   API_BEGIN();
   CHECK_HANDLE();
-  HostDeviceVector<bst_float>& preds =
-      XGBAPIThreadLocalStore::Get()->ret_vec_float;
   auto *bst = static_cast<Learner*>(handle);
+  HostDeviceVector<bst_float> tmp_preds;
   bst->Predict(
       *static_cast<std::shared_ptr<DMatrix>*>(dmat),
       (option_mask & 1) != 0,
-      &preds, ntree_limit,
+      &tmp_preds, ntree_limit,
       static_cast<bool>(training),
       (option_mask & 2) != 0,
       (option_mask & 4) != 0,
       (option_mask & 8) != 0,
       (option_mask & 16) != 0);
-  *out_result = dmlc::BeginPtr(preds.HostVector());
-  *len = static_cast<xgboost::bst_ulong>(preds.Size());
+  preds = tmp_preds.HostVector();
+  *out_result = dmlc::BeginPtr(preds);
+  *len = static_cast<xgboost::bst_ulong>(preds.size());
   API_END();
 }