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From paul-rogers <...@git.apache.org>
Subject [GitHub] drill pull request #921: DRILL-4286 Graceful shutdown of drillbit
Date Tue, 14 Nov 2017 22:41:48 GMT
Github user paul-rogers commented on a diff in the pull request:

    https://github.com/apache/drill/pull/921#discussion_r150976659
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/server/DrillbitStateManager.java
---
    @@ -0,0 +1,80 @@
    +/*
    + * 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.drill.exec.server;
    +/*
    +  State manager to manage the state of drillbit.
    + */
    +public class DrillbitStateManager {
    +
    +
    +  public DrillbitStateManager(DrillbitState currentState) {
    +    this.currentState = currentState;
    +  }
    +
    +  public enum DrillbitState {
    +    STARTUP, ONLINE, GRACE, DRAINING, OFFLINE, SHUTDOWN
    +  }
    +
    +  public DrillbitState getState() {
    +    return currentState;
    +  }
    +
    +  private DrillbitState currentState;
    +  public void setState(DrillbitState state) {
    +    switch (state) {
    +      case ONLINE:
    +        if (currentState == DrillbitState.STARTUP) {
    +          currentState = state;
    +        } else {
    +          throw new IllegalStateException("Cannot set drillbit to" + state + "from" +
currentState);
    --- End diff --
    
    To avoid redundant code and to catch new states:
    
    ```
    setState(State newState) {
      currentState = transitionTo(newState);
    }
    
    State transitionTo(State newState) {
      switch (newState) {
        case ONLINE:
          if (currentState == DrillbitState.STARTUP) {
            return newState;
          }
          break;
        ...
        default:
          break;
        }
      throw new IllegalStateException("Cannot set drillbit to" + state + "from" + currentState);
    ```
    
    An alternative is to switch on current state to say, essentially "if we are in state X,
we allow transition to states Y and Z." But, that may be overkill here.


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