xgboost/jvm-packages/xgboost4j/src/native/xgboost4j.cpp

/*
  Copyright (c) 2014 by Contributors
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0
  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

#include <cstdint>
#include <xgboost/c_api.h>
#include <xgboost/base.h>
#include <xgboost/logging.h>
#include "./xgboost4j.h"
#include <cstring>
#include <vector>
#include <string>

// helper functions
// set handle
void setHandle(JNIEnv *jenv, jlongArray jhandle, void* handle) {
#ifdef __APPLE__
  jlong out = (long) handle;
#else
  int64_t out = (int64_t) handle;
#endif
  jenv->SetLongArrayRegion(jhandle, 0, 1, &out);
}

// global JVM
static JavaVM* global_jvm = nullptr;

// overrides JNI on load
jint JNI_OnLoad(JavaVM *vm, void *reserved) {
  global_jvm = vm;
  return JNI_VERSION_1_6;
}

XGB_EXTERN_C int XGBoost4jCallbackDataIterNext(
    DataIterHandle data_handle,
    XGBCallbackSetData* set_function,
    DataHolderHandle set_function_handle) {
  jobject jiter = static_cast<jobject>(data_handle);
  JNIEnv* jenv;
  int jni_status = global_jvm->GetEnv((void **)&jenv, JNI_VERSION_1_6);
  if (jni_status == JNI_EDETACHED) {
    global_jvm->AttachCurrentThread(reinterpret_cast<void **>(&jenv), nullptr);
  } else {
    CHECK(jni_status == JNI_OK);
  }
  try {
    jclass iterClass = jenv->FindClass("java/util/Iterator");
    jmethodID hasNext = jenv->GetMethodID(iterClass,
                                          "hasNext", "()Z");
    jmethodID next = jenv->GetMethodID(iterClass,
                                       "next", "()Ljava/lang/Object;");
    int ret_value;
    if (jenv->CallBooleanMethod(jiter, hasNext)) {
      ret_value = 1;
      jobject batch = jenv->CallObjectMethod(jiter, next);
      jclass batchClass = jenv->GetObjectClass(batch);
      jlongArray joffset = (jlongArray)jenv->GetObjectField(
          batch, jenv->GetFieldID(batchClass, "rowOffset", "[J"));
      jfloatArray jlabel = (jfloatArray)jenv->GetObjectField(
          batch, jenv->GetFieldID(batchClass, "label", "[F"));
      jfloatArray jweight = (jfloatArray)jenv->GetObjectField(
          batch, jenv->GetFieldID(batchClass, "weight", "[F"));
      jintArray jindex = (jintArray)jenv->GetObjectField(
          batch, jenv->GetFieldID(batchClass, "featureIndex", "[I"));
      jfloatArray jvalue = (jfloatArray)jenv->GetObjectField(
        batch, jenv->GetFieldID(batchClass, "featureValue", "[F"));
      XGBoostBatchCSR cbatch;
      cbatch.size = jenv->GetArrayLength(joffset) - 1;
      cbatch.offset = reinterpret_cast<long *>(
          jenv->GetLongArrayElements(joffset, 0));
      if (jlabel != nullptr) {
        cbatch.label = jenv->GetFloatArrayElements(jlabel, 0);
        CHECK_EQ(jenv->GetArrayLength(jlabel), static_cast<long>(cbatch.size))
            << "batch.label.length must equal batch.numRows()";
      } else {
        cbatch.label = nullptr;
      }
      if (jweight != nullptr) {
        cbatch.weight = jenv->GetFloatArrayElements(jweight, 0);
        CHECK_EQ(jenv->GetArrayLength(jweight), static_cast<long>(cbatch.size))
            << "batch.weight.length must equal batch.numRows()";
      } else {
        cbatch.weight = nullptr;
      }
      long max_elem = cbatch.offset[cbatch.size];
      cbatch.index = (int*) jenv->GetIntArrayElements(jindex, 0);
      cbatch.value = jenv->GetFloatArrayElements(jvalue, 0);

      CHECK_EQ(jenv->GetArrayLength(jindex), max_elem)
          << "batch.index.length must equal batch.offset.back()";
      CHECK_EQ(jenv->GetArrayLength(jvalue), max_elem)
          << "batch.index.length must equal batch.offset.back()";
      // cbatch is ready
      CHECK_EQ((*set_function)(set_function_handle, cbatch), 0)
          << XGBGetLastError();
      // release the elements.
      jenv->ReleaseLongArrayElements(
          joffset, reinterpret_cast<jlong *>(cbatch.offset), 0);
      jenv->DeleteLocalRef(joffset);
      if (jlabel != nullptr) {
        jenv->ReleaseFloatArrayElements(jlabel, cbatch.label, 0);
        jenv->DeleteLocalRef(jlabel);
      }
      if (jweight != nullptr) {
        jenv->ReleaseFloatArrayElements(jweight, cbatch.weight, 0);
        jenv->DeleteLocalRef(jweight);
      }
      jenv->ReleaseIntArrayElements(jindex, (jint*) cbatch.index, 0);
      jenv->DeleteLocalRef(jindex);
      jenv->ReleaseFloatArrayElements(jvalue, cbatch.value, 0);
      jenv->DeleteLocalRef(jvalue);
      jenv->DeleteLocalRef(batch);
      jenv->DeleteLocalRef(batchClass);
      ret_value = 1;
    } else {
      ret_value = 0;
    }
    jenv->DeleteLocalRef(iterClass);
    // only detach if it is a async call.
    if (jni_status == JNI_EDETACHED) {
      global_jvm->DetachCurrentThread();
    }
    return ret_value;
  } catch(dmlc::Error e) {
    // only detach if it is a async call.
    if (jni_status == JNI_EDETACHED) {
      global_jvm->DetachCurrentThread();
    }
    LOG(FATAL) << e.what();
    return -1;
  }
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBGetLastError
 * Signature: ()Ljava/lang/String;
 */
JNIEXPORT jstring JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBGetLastError
  (JNIEnv *jenv, jclass jcls) {
  jstring jresult = 0;
  const char* result = XGBGetLastError();
  if (result != NULL) {
    jresult = jenv->NewStringUTF(result);
  }
  return jresult;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixCreateFromDataIter
 * Signature: (Ljava/util/Iterator;Ljava/lang/String;[J)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixCreateFromDataIter
  (JNIEnv *jenv, jclass jcls, jobject jiter, jstring jcache_info, jlongArray jout) {
  DMatrixHandle result;
  const char* cache_info = nullptr;
  if (jcache_info != nullptr) {
    cache_info = jenv->GetStringUTFChars(jcache_info, 0);
  }
  int ret = XGDMatrixCreateFromDataIter(
      jiter, XGBoost4jCallbackDataIterNext, cache_info, &result);
  if (cache_info) {
    jenv->ReleaseStringUTFChars(jcache_info, cache_info);
  }
  setHandle(jenv, jout, result);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixCreateFromFile
 * Signature: (Ljava/lang/String;I[J)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixCreateFromFile
  (JNIEnv *jenv, jclass jcls, jstring jfname, jint jsilent, jlongArray jout) {
  DMatrixHandle result;
  const char* fname = jenv->GetStringUTFChars(jfname, 0);
  int ret = XGDMatrixCreateFromFile(fname, jsilent, &result);
  if (fname) {
    jenv->ReleaseStringUTFChars(jfname, fname);
  }
  setHandle(jenv, jout, result);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixCreateFromCSREx
 * Signature: ([J[J[F)J
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixCreateFromCSREx
  (JNIEnv *jenv, jclass jcls, jlongArray jindptr, jintArray jindices, jfloatArray jdata, jint jcol, jlongArray jout) {
  DMatrixHandle result;
  jlong* indptr = jenv->GetLongArrayElements(jindptr, 0);
  jint* indices = jenv->GetIntArrayElements(jindices, 0);
  jfloat* data = jenv->GetFloatArrayElements(jdata, 0);
  bst_ulong nindptr = (bst_ulong)jenv->GetArrayLength(jindptr);
  bst_ulong nelem = (bst_ulong)jenv->GetArrayLength(jdata);
  jint ret = (jint) XGDMatrixCreateFromCSREx((size_t const *)indptr, (unsigned int const *)indices, (float const *)data, nindptr, nelem, jcol, &result);
  setHandle(jenv, jout, result);
  //Release
  jenv->ReleaseLongArrayElements(jindptr, indptr, 0);
  jenv->ReleaseIntArrayElements(jindices, indices, 0);
  jenv->ReleaseFloatArrayElements(jdata, data, 0);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixCreateFromCSCEx
 * Signature: ([J[J[F)J
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixCreateFromCSCEx
  (JNIEnv *jenv, jclass jcls, jlongArray jindptr, jintArray jindices, jfloatArray jdata, jint jrow, jlongArray jout) {
  DMatrixHandle result;
  jlong* indptr = jenv->GetLongArrayElements(jindptr, NULL);
  jint* indices = jenv->GetIntArrayElements(jindices, 0);
  jfloat* data = jenv->GetFloatArrayElements(jdata, NULL);
  bst_ulong nindptr = (bst_ulong)jenv->GetArrayLength(jindptr);
  bst_ulong nelem = (bst_ulong)jenv->GetArrayLength(jdata);

  jint ret = (jint) XGDMatrixCreateFromCSCEx((size_t const *)indptr, (unsigned int const *)indices, (float const *)data, nindptr, nelem, jrow, &result);
  setHandle(jenv, jout, result);
  //release
  jenv->ReleaseLongArrayElements(jindptr, indptr, 0);
  jenv->ReleaseIntArrayElements(jindices, indices, 0);
  jenv->ReleaseFloatArrayElements(jdata, data, 0);

  return ret;
}


/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixCreateFromMat
 * Signature: ([FIIF)J
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixCreateFromMat
  (JNIEnv *jenv, jclass jcls, jfloatArray jdata, jint jnrow, jint jncol, jfloat jmiss, jlongArray jout) {
  DMatrixHandle result;
  jfloat* data = jenv->GetFloatArrayElements(jdata, 0);
  bst_ulong nrow = (bst_ulong)jnrow;
  bst_ulong ncol = (bst_ulong)jncol;
  jint ret = (jint) XGDMatrixCreateFromMat((float const *)data, nrow, ncol, jmiss, &result);
  setHandle(jenv, jout, result);
  //release
  jenv->ReleaseFloatArrayElements(jdata, data, 0);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixSliceDMatrix
 * Signature: (J[I)J
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixSliceDMatrix
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jintArray jindexset, jlongArray jout) {
  DMatrixHandle result;
  DMatrixHandle handle = (DMatrixHandle) jhandle;

  jint* indexset = jenv->GetIntArrayElements(jindexset, 0);
  bst_ulong len = (bst_ulong)jenv->GetArrayLength(jindexset);

  jint ret = (jint) XGDMatrixSliceDMatrix(handle, (int const *)indexset, len, &result);
  setHandle(jenv, jout, result);
  //release
  jenv->ReleaseIntArrayElements(jindexset, indexset, 0);

  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixFree
 * Signature: (J)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixFree
  (JNIEnv *jenv, jclass jcls, jlong jhandle) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  int ret = XGDMatrixFree(handle);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixSaveBinary
 * Signature: (JLjava/lang/String;I)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixSaveBinary
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfname, jint jsilent) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  const char* fname = jenv->GetStringUTFChars(jfname, 0);
  int ret = XGDMatrixSaveBinary(handle, fname, jsilent);
  if (fname) jenv->ReleaseStringUTFChars(jfname, (const char *)fname);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixSetFloatInfo
 * Signature: (JLjava/lang/String;[F)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixSetFloatInfo
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfield, jfloatArray jarray) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  const char*  field = jenv->GetStringUTFChars(jfield, 0);

  jfloat* array = jenv->GetFloatArrayElements(jarray, NULL);
  bst_ulong len = (bst_ulong)jenv->GetArrayLength(jarray);
  int ret = XGDMatrixSetFloatInfo(handle, field, (float const *)array, len);
  //release
  if (field) jenv->ReleaseStringUTFChars(jfield, field);
  jenv->ReleaseFloatArrayElements(jarray, array, 0);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixSetUIntInfo
 * Signature: (JLjava/lang/String;[I)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixSetUIntInfo
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfield, jintArray jarray) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  const char*  field = jenv->GetStringUTFChars(jfield, 0);
  jint* array = jenv->GetIntArrayElements(jarray, NULL);
  bst_ulong len = (bst_ulong)jenv->GetArrayLength(jarray);
  int ret = XGDMatrixSetUIntInfo(handle, (char const *)field, (unsigned int const *)array, len);
  //release
  if (field) jenv->ReleaseStringUTFChars(jfield, (const char *)field);
  jenv->ReleaseIntArrayElements(jarray, array, 0);

  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixSetGroup
 * Signature: (J[I)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixSetGroup
  (JNIEnv * jenv, jclass jcls, jlong jhandle, jintArray jarray) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  jint* array = jenv->GetIntArrayElements(jarray, NULL);
  bst_ulong len = (bst_ulong)jenv->GetArrayLength(jarray);
  int ret = XGDMatrixSetGroup(handle, (unsigned int const *)array, len);
  //release
  jenv->ReleaseIntArrayElements(jarray, array, 0);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixGetFloatInfo
 * Signature: (JLjava/lang/String;)[F
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixGetFloatInfo
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfield, jobjectArray jout) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  const char*  field = jenv->GetStringUTFChars(jfield, 0);
  bst_ulong len;
  float *result;
  int ret = XGDMatrixGetFloatInfo(handle, field, &len, (const float**) &result);
  if (field) jenv->ReleaseStringUTFChars(jfield, field);

  jsize jlen = (jsize) len;
  jfloatArray jarray = jenv->NewFloatArray(jlen);
  jenv->SetFloatArrayRegion(jarray, 0, jlen, (jfloat *) result);
  jenv->SetObjectArrayElement(jout, 0, (jobject) jarray);

  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixGetUIntInfo
 * Signature: (JLjava/lang/String;)[I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixGetUIntInfo
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfield, jobjectArray jout) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  const char*  field = jenv->GetStringUTFChars(jfield, 0);
  bst_ulong len;
  unsigned int *result;
  int ret = (jint) XGDMatrixGetUIntInfo(handle, field, &len, (const unsigned int **) &result);
  if (field) jenv->ReleaseStringUTFChars(jfield, field);

  jsize jlen = (jsize) len;
  jintArray jarray = jenv->NewIntArray(jlen);
  jenv->SetIntArrayRegion(jarray, 0, jlen, (jint *) result);
  jenv->SetObjectArrayElement(jout, 0, jarray);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGDMatrixNumRow
 * Signature: (J)J
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGDMatrixNumRow
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jlongArray jout) {
  DMatrixHandle handle = (DMatrixHandle) jhandle;
  bst_ulong result[1];
  int ret = (jint) XGDMatrixNumRow(handle, result);
  jenv->SetLongArrayRegion(jout, 0, 1, (const jlong *) result);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterCreate
 * Signature: ([J)J
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterCreate
  (JNIEnv *jenv, jclass jcls, jlongArray jhandles, jlongArray jout) {
  std::vector<DMatrixHandle> handles;
  if (jhandles != nullptr) {
    size_t len = jenv->GetArrayLength(jhandles);
    jlong *cjhandles = jenv->GetLongArrayElements(jhandles, 0);
    for (size_t i = 0; i < len; ++i) {
      handles.push_back((DMatrixHandle) cjhandles[i]);
    }
    jenv->ReleaseLongArrayElements(jhandles, cjhandles, 0);
  }
  BoosterHandle result;
  int ret = XGBoosterCreate(dmlc::BeginPtr(handles), handles.size(), &result);
  setHandle(jenv, jout, result);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterFree
 * Signature: (J)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterFree
  (JNIEnv *jenv, jclass jcls, jlong jhandle) {
    BoosterHandle handle = (BoosterHandle) jhandle;
    return XGBoosterFree(handle);
}


/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterSetParam
 * Signature: (JLjava/lang/String;Ljava/lang/String;)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterSetParam
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jname, jstring jvalue) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  const char* name = jenv->GetStringUTFChars(jname, 0);
  const char* value = jenv->GetStringUTFChars(jvalue, 0);
  int ret = XGBoosterSetParam(handle, name, value);
  //release
  if (name) jenv->ReleaseStringUTFChars(jname, name);
  if (value) jenv->ReleaseStringUTFChars(jvalue, value);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterUpdateOneIter
 * Signature: (JIJ)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterUpdateOneIter
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jint jiter, jlong jdtrain) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  DMatrixHandle dtrain = (DMatrixHandle) jdtrain;
  return XGBoosterUpdateOneIter(handle, jiter, dtrain);
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterBoostOneIter
 * Signature: (JJ[F[F)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterBoostOneIter
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jlong jdtrain, jfloatArray jgrad, jfloatArray jhess) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  DMatrixHandle dtrain = (DMatrixHandle) jdtrain;
  jfloat* grad = jenv->GetFloatArrayElements(jgrad, 0);
  jfloat* hess = jenv->GetFloatArrayElements(jhess, 0);
  bst_ulong len = (bst_ulong)jenv->GetArrayLength(jgrad);
  int ret = XGBoosterBoostOneIter(handle, dtrain, grad, hess, len);
  //release
  jenv->ReleaseFloatArrayElements(jgrad, grad, 0);
  jenv->ReleaseFloatArrayElements(jhess, hess, 0);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterEvalOneIter
 * Signature: (JI[J[Ljava/lang/String;)Ljava/lang/String;
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterEvalOneIter
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jint jiter, jlongArray jdmats, jobjectArray jevnames, jobjectArray jout) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  std::vector<DMatrixHandle> dmats;
  std::vector<std::string> evnames;
  std::vector<const char*> evchars;

  size_t len =  static_cast<size_t>(jenv->GetArrayLength(jdmats));
  // put handle from jhandles to chandles
  jlong* cjdmats = jenv->GetLongArrayElements(jdmats, 0);
  for (size_t i = 0; i < len; ++i) {
    dmats.push_back((DMatrixHandle) cjdmats[i]);
    jstring jevname = (jstring)jenv->GetObjectArrayElement(jevnames, i);
    const char *s =jenv->GetStringUTFChars(jevname, 0);
    evnames.push_back(std::string(s, jenv->GetStringLength(jevname)));
    if (s != nullptr) jenv->ReleaseStringUTFChars(jevname, s);
  }
  jenv->ReleaseLongArrayElements(jdmats, cjdmats, 0);
  for (size_t i = 0; i < len; ++i) {
    evchars.push_back(evnames[i].c_str());
  }
  const char* result;
  int ret = XGBoosterEvalOneIter(handle, jiter,
                                 dmlc::BeginPtr(dmats),
                                 dmlc::BeginPtr(evchars),
                                 len, &result);
  jstring jinfo = nullptr;
  if (result != nullptr) {
    jinfo = jenv->NewStringUTF(result);
  }
  jenv->SetObjectArrayElement(jout, 0, jinfo);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterPredict
 * Signature: (JJIJ)[F
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterPredict
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jlong jdmat, jint joption_mask, jint jntree_limit, jobjectArray jout) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  DMatrixHandle dmat = (DMatrixHandle) jdmat;
  bst_ulong len;
  float *result;
  int ret = XGBoosterPredict(handle, dmat, joption_mask, (unsigned int) jntree_limit, &len, (const float **) &result);

  jsize jlen = (jsize) len;
  jfloatArray jarray = jenv->NewFloatArray(jlen);
  jenv->SetFloatArrayRegion(jarray, 0, jlen, (jfloat *) result);
  jenv->SetObjectArrayElement(jout, 0, jarray);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterLoadModel
 * Signature: (JLjava/lang/String;)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterLoadModel
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfname) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  const char* fname = jenv->GetStringUTFChars(jfname, 0);

  int ret = XGBoosterLoadModel(handle, fname);
  if (fname) jenv->ReleaseStringUTFChars(jfname,fname);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterSaveModel
 * Signature: (JLjava/lang/String;)V
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterSaveModel
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfname) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  const char*  fname = jenv->GetStringUTFChars(jfname, 0);

  int ret = XGBoosterSaveModel(handle, fname);
  if (fname) jenv->ReleaseStringUTFChars(jfname, fname);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterLoadModelFromBuffer
 * Signature: (J[B)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterLoadModelFromBuffer
    (JNIEnv *jenv, jclass jcls, jlong jhandle, jbyteArray jbytes) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  jbyte* buffer = jenv->GetByteArrayElements(jbytes, 0);
  int ret = XGBoosterLoadModelFromBuffer(
      handle, buffer, jenv->GetArrayLength(jbytes));
  jenv->ReleaseByteArrayElements(jbytes, buffer, 0);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterGetModelRaw
 * Signature: (J[[B)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterGetModelRaw
  (JNIEnv * jenv, jclass jcls, jlong jhandle, jobjectArray jout) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  bst_ulong len = 0;
  const char* result;
  int ret = XGBoosterGetModelRaw(handle, &len, &result);

  if (result) {
    jbyteArray jarray = jenv->NewByteArray(len);
    jenv->SetByteArrayRegion(jarray, 0, len, (jbyte*)result);
    jenv->SetObjectArrayElement(jout, 0, jarray);
  }
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterDumpModelEx
 * Signature: (JLjava/lang/String;I)[Ljava/lang/String;
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterDumpModelEx
  (JNIEnv *jenv, jclass jcls, jlong jhandle, jstring jfmap, jint jwith_stats, jstring jformat, jobjectArray jout) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  const char *fmap = jenv->GetStringUTFChars(jfmap, 0);
  const char *format = jenv->GetStringUTFChars(jformat, 0);
  bst_ulong len = 0;
  char **result;

  int ret = XGBoosterDumpModelEx(handle, fmap, jwith_stats, format, &len, (const char ***) &result);

  jsize jlen = (jsize) len;
  jobjectArray jinfos = jenv->NewObjectArray(jlen, jenv->FindClass("java/lang/String"), jenv->NewStringUTF(""));
  for(int i=0 ; i<jlen; i++) {
    jenv->SetObjectArrayElement(jinfos, i, jenv->NewStringUTF((const char*) result[i]));
  }
  jenv->SetObjectArrayElement(jout, 0, jinfos);

  if (fmap) jenv->ReleaseStringUTFChars(jfmap, (const char *)fmap);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterLoadRabitCheckpoint
 * Signature: (J[I)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterLoadRabitCheckpoint
  (JNIEnv *jenv , jclass jcls, jlong jhandle, jintArray jout) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  int version;
  int ret = XGBoosterLoadRabitCheckpoint(handle, &version);
  jint jversion = version;
  jenv->SetIntArrayRegion(jout, 0, 1, &jversion);
  return ret;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    XGBoosterSaveRabitCheckpoint
 * Signature: (J)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_XGBoosterSaveRabitCheckpoint
  (JNIEnv *jenv, jclass jcls, jlong jhandle) {
  BoosterHandle handle = (BoosterHandle) jhandle;
  return XGBoosterSaveRabitCheckpoint(handle);
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    RabitInit
 * Signature: ([Ljava/lang/String;)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitInit
  (JNIEnv *jenv, jclass jcls, jobjectArray jargs) {
  std::vector<std::string> args;
  std::vector<char*> argv;
  bst_ulong len = (bst_ulong)jenv->GetArrayLength(jargs);
  for (bst_ulong i = 0; i < len; ++i) {
    jstring arg = (jstring)jenv->GetObjectArrayElement(jargs, i);
    const char *s = jenv->GetStringUTFChars(arg, 0);
    args.push_back(std::string(s, jenv->GetStringLength(arg)));
    if (s != nullptr) jenv->ReleaseStringUTFChars(arg, s);
    if (args.back().length() == 0) args.pop_back();
  }

  for (size_t i = 0; i < args.size(); ++i) {
    argv.push_back(&args[i][0]);
  }

  RabitInit(args.size(), dmlc::BeginPtr(argv));
  return 0;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    RabitFinalize
 * Signature: ()I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitFinalize
  (JNIEnv *jenv, jclass jcls) {
  RabitFinalize();
  return 0;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    RabitTrackerPrint
 * Signature: (Ljava/lang/String;)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitTrackerPrint
  (JNIEnv *jenv, jclass jcls, jstring jmsg) {
  std::string str(jenv->GetStringUTFChars(jmsg, 0),
                  jenv->GetStringLength(jmsg));
  RabitTrackerPrint(str.c_str());
  return 0;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    RabitGetRank
 * Signature: ([I)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitGetRank
  (JNIEnv *jenv, jclass jcls, jintArray jout) {
  jint rank = RabitGetRank();
  jenv->SetIntArrayRegion(jout, 0, 1, &rank);
  return 0;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    RabitGetWorldSize
 * Signature: ([I)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitGetWorldSize
  (JNIEnv *jenv, jclass jcls, jintArray jout) {
  jint out = RabitGetWorldSize();
  jenv->SetIntArrayRegion(jout, 0, 1, &out);
  return 0;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    RabitVersionNumber
 * Signature: ([I)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitVersionNumber
  (JNIEnv *jenv, jclass jcls, jintArray jout) {
  jint out = RabitVersionNumber();
  jenv->SetIntArrayRegion(jout, 0, 1, &out);
  return 0;
}

/*
 * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
 * Method:    RabitAllreduce
 * Signature: (Ljava/nio/ByteBuffer;III)I
 */
JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitAllreduce
  (JNIEnv *jenv, jclass jcls, jobject jsendrecvbuf, jint jcount, jint jenum_dtype, jint jenum_op) {
  void *ptr_sendrecvbuf = jenv->GetDirectBufferAddress(jsendrecvbuf);
  RabitAllreduce(ptr_sendrecvbuf, (size_t) jcount, jenum_dtype, jenum_op, NULL, NULL);

  return 0;
}