content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file 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.
   */
  package org.apache.calcite.plan.hep;
  
  /** Able to execute an instruction or program, and contains all mutable state
   * for that instruction.
   *
   * <p>The goal is that programs are re-entrant - they can be used by more than
   * one thread at a time. We achieve this by making instructions and programs
   * immutable. All mutable state is held in the state objects.
   *
   * <p>State objects are allocated, just before the program is executed, by
   * calling {@link HepInstruction#prepare(HepInstruction.PrepareContext)} on the
   * program and recursively on all of its instructions. */
  abstract class HepState {
    final HepPlanner planner;
    final HepProgram.State programState;
  
    HepState(HepInstruction.PrepareContext px) {
      this.planner = px.planner;
      this.programState = px.programState;
    }
  
    /** Executes the instruction. */
    abstract void execute();
  
    /** Re-initializes the state. (The state was initialized when it was created
     * via {@link HepInstruction#prepare}.) */
    void init() {
    }
  }
  