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// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you 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.


#ifndef IMPALA_EXPRS_HIVE_UDF_CALL_H
#define IMPALA_EXPRS_HIVE_UDF_CALL_H

#include <jni.h>
#include <string>
#include <boost/scoped_ptr.hpp>

#include "exprs/scalar-expr.h"

namespace impala {

using impala_udf::FunctionContext;
using impala_udf::AnyVal;
using impala_udf::BooleanVal;
using impala_udf::TinyIntVal;
using impala_udf::SmallIntVal;
using impala_udf::IntVal;
using impala_udf::BigIntVal;
using impala_udf::FloatVal;
using impala_udf::DoubleVal;
using impala_udf::TimestampVal;
using impala_udf::StringVal;
using impala_udf::DecimalVal;
using impala_udf::DateVal;

class RuntimeState;
class ScalarExprEvaluator;
class TExprNode;

/// Executor for hive udfs using JNI. This works with the UdfExecutor on the
/// java side which calls into the actual UDF.
//
/// To minimize the JNI overhead, we eliminate as many copies as possible and
/// share memory between the native side and java side. Memory in the native heap
/// can be read with no issues from java but not vice versa (ptrs in the java heap
/// move). Also, JNI calls are cheaper for function calls with no arguments and
/// no return value (void).
//
/// During Prepare(), we allocate an input buffer that is big enough to store
/// all of the inputs (i.e. the slot size). This buffer is passed to the UdfExecutor
/// in the constructor. During Evaluate(), the input buffer is populated and
/// the UdfExecutor.evaluate() method is called via JNI. For input arguments,
/// strings don't need to be treated any differently. The java side can parse
/// the ptr and length from the StringValue and then read the ptr directly.
//
/// For return values that are fixed size (i.e. not strings), we allocate an
/// output buffer in Prepare(). This is also passed to the UdfExecutor in the
/// constructor. The UdfExecutor writes to it directly during evaluate().
//
/// For strings, we pass a StringValue sized output buffer to the FE. The address
/// of the StringValue does not change. When the FE writes the string result, it
/// populates the StringValue with the buffer it allocated from its native heap.
/// The BE reads the StringValue as normal.
//
/// If the UDF ran into an error, the FE throws an exception.
class HiveUdfCall : public ScalarExpr {
 public:
  /// Must be called before creating any HiveUdfCall instances. This is called at impalad
  /// startup time.
  static Status InitEnv() WARN_UNUSED_RESULT;

  virtual Status GetCodegendComputeFnImpl(LlvmCodeGen* codegen, llvm::Function** fn)
      override WARN_UNUSED_RESULT;
  virtual std::string DebugString() const override;

 protected:
  friend class ScalarExpr;
  friend class ScalarExprEvaluator;
  friend class StringFunctions;

  virtual bool HasFnCtx() const override { return true; }

  HiveUdfCall(const TExprNode& node);

  virtual Status Init(const RowDescriptor& row_desc, bool is_entry_point,
      RuntimeState* state) override WARN_UNUSED_RESULT;
  virtual Status OpenEvaluator(FunctionContext::FunctionStateScope scope,
      RuntimeState* state, ScalarExprEvaluator* eval) const override WARN_UNUSED_RESULT;
  virtual void CloseEvaluator(FunctionContext::FunctionStateScope scope,
      RuntimeState* state, ScalarExprEvaluator* eval) const override;

  GENERATE_GET_VAL_INTERPRETED_OVERRIDES_FOR_ALL_SCALAR_TYPES

 private:
  /// Evalutes the UDF over row. Returns the result as an AnyVal. This function
  /// never returns NULL but rather an AnyVal object with is_null set to true on
  /// error.
  AnyVal* Evaluate(ScalarExprEvaluator* eval, const TupleRow* row) const;

  /// input_byte_offsets_[i] is the byte offset child ith's input argument should
  /// be written to.
  std::vector<int> input_byte_offsets_;

  /// The size of the buffer for passing in input arguments.
  int input_buffer_size_;

  /// Global class reference to the UdfExecutor Java class and related method IDs. Set in
  /// Init(). These have the lifetime of the process (i.e. 'executor_cl_' is never freed).
  static jclass executor_cl_;
  static jmethodID executor_ctor_id_;
  static jmethodID executor_evaluate_id_;
  static jmethodID executor_close_id_;
};

}

#endif