JNI wrapper for the collective communicator (#8242)

jvm-packages/xgboost4j/src/native/xgboost4j.h

@@ -335,6 +335,54 @@ JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitVersionNumber
 JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_RabitAllreduce
   (JNIEnv *, jclass, jobject, jint, jint, jint);
 
+/*
+ * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
+ * Method:    CommunicatorInit
+ * Signature: ([Ljava/lang/String;)I
+ */
+JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_CommunicatorInit
+  (JNIEnv *, jclass, jobjectArray);
+
+/*
+ * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
+ * Method:    CommunicatorFinalize
+ * Signature: ()I
+ */
+JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_CommunicatorFinalize
+  (JNIEnv *, jclass);
+
+/*
+ * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
+ * Method:    CommunicatorPrint
+ * Signature: (Ljava/lang/String;)I
+ */
+JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_CommunicatorPrint
+  (JNIEnv *, jclass, jstring);
+
+/*
+ * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
+ * Method:    CommunicatorGetRank
+ * Signature: ([I)I
+ */
+JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_CommunicatorGetRank
+  (JNIEnv *, jclass, jintArray);
+
+/*
+ * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
+ * Method:    CommunicatorGetWorldSize
+ * Signature: ([I)I
+ */
+JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_CommunicatorGetWorldSize
+  (JNIEnv *, jclass, jintArray);
+
+/*
+ * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
+ * Method:    CommunicatorAllreduce
+ * Signature: (Ljava/nio/ByteBuffer;III)I
+ */
+JNIEXPORT jint JNICALL Java_ml_dmlc_xgboost4j_java_XGBoostJNI_CommunicatorAllreduce
+  (JNIEnv *, jclass, jobject, jint, jint, jint);
+
 /*
  * Class:     ml_dmlc_xgboost4j_java_XGBoostJNI
  * Method:    XGDMatrixSetInfoFromInterface