hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/container/replication/health/AbstractCheck.java

/*
 * 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.hadoop.hdds.scm.container.replication.health;

import org.apache.hadoop.hdds.scm.container.replication.ContainerCheckRequest;

/**
 * Abstract base class for Container Health Checks to extend.
 */
public abstract class AbstractCheck implements HealthCheck {

  private HealthCheck successor = null;

  /**
   * Handle the container and apply the given check to it. This may result in
   * commands getting generated to correct container states, or nothing
   * happening if the container is healthy.
   * @param request ContainerCheckRequest object representing the container
   * @return True if the request was handled or false if it was not and should
   *         be handled by the next handler in the chain.
   */
  public boolean handleChain(ContainerCheckRequest request) {
    boolean result = handle(request);
    if (!result && successor != null) {
      return successor.handleChain(request);
    }
    return result;
  }

  /**
   * Add a subsequent HealthCheck that will be tried only if the current check
   * returns false. This allows handlers to be chained together, and each will
   * be tried in turn until one succeeds.
   * @param healthCheck The HealthCheck to add to the successor, which will be
   *                    tried if the current check returns false.
   * @return The passed in health check, so the next check in the chain can be
   *         easily added to the successor.
   */
  @Override
  public HealthCheck addNext(HealthCheck healthCheck) {
    successor = healthCheck;
    return healthCheck;
  }

  /**
   * Handle the container and apply the given check to it. This may result in
   * commands getting generated to correct container states, or nothing
   * happening if the container is healthy.
   * @param request ContainerCheckRequest object representing the container
   * @return True if the request was handled or false if it was not and should
   *         be handled by the next handler in the chain.
   */
  @Override
  public abstract boolean handle(ContainerCheckRequest request);

}