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.volcano;
  
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.util.trace.CalciteTrace;
  
  import org.slf4j.Logger;
  
  import static java.util.Objects.requireNonNull;
  
  /***
   * The algorithm executes repeatedly. The exact rules
   * that may be fired varies.
   *
   * <p>The planner iterates over the rule matches presented
   * by the rule queue until the rule queue becomes empty.
   */
  class IterativeRuleDriver implements RuleDriver {
  
    private static final Logger LOGGER = CalciteTrace.getPlannerTracer();
  
    private final VolcanoPlanner planner;
    private final IterativeRuleQueue ruleQueue;
  
    IterativeRuleDriver(VolcanoPlanner planner) {
      this.planner = planner;
      ruleQueue = new IterativeRuleQueue(planner);
    }
  
    @Override public IterativeRuleQueue getRuleQueue() {
      return ruleQueue;
    }
  
    @Override public void drive() {
      while (true) {
        requireNonNull(planner.root, "RelSubset must not be null at this point");
        LOGGER.debug("Best cost before rule match: {}", planner.root.bestCost);
  
        VolcanoRuleMatch match = ruleQueue.popMatch();
        if (match == null) {
          break;
        }
  
        assert match.getRule().matches(match);
        try {
          match.onMatch();
        } catch (VolcanoTimeoutException e) {
          LOGGER.warn("Volcano planning times out, cancels the subsequent optimization.");
          planner.canonize();
          break;
        }
  
        // The root may have been merged with another
        // subset. Find the new root subset.
        planner.canonize();
      }
  
    }
  
    @Override public void onProduce(RelNode rel, RelSubset subset) {
    }
  
    @Override public void onSetMerged(RelSet set) {
    }
  
    @Override public void clear() {
      ruleQueue.clear();
    }
  }
  