content: /*
   * Tencent is pleased to support the open source community by making Angel available.
   *
   * Copyright (C) 2017-2018 THL A29 Limited, a Tencent company. All rights reserved.
   *
   * Licensed 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
   *
   * https://opensource.org/licenses/Apache-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 com.tencent.angel;
  
  import com.tencent.angel.utils.HasThread;
  import com.tencent.angel.utils.Sleeper;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Chore is a task performed on a period in hbase. The chore is run in its own thread. This base
   * abstract class provides while loop and sleeping facility. If an unhandled exception, the threads
   * exit is logged. Implementers just need to add checking if there is work to be done and if so, do
   * it. Its the base of most of the chore threads in hbase.
   * <p>
   * <p>
   * Don't subclass Chore if the task relies on being woken up for something to do, such as an entry
   * being added to a queue, etc.
   */
  public abstract class Chore extends HasThread {
    private final Logger LOG = LoggerFactory.getLogger(this.getClass());
    private final Sleeper sleeper;
    protected final Stoppable stopper;
  
    /**
     * @param p       Period at which we should run. Will be adjusted appropriately should we find work and
     *                it takes time to complete.
     * @param stopper When {@link Stoppable#isStopped()} is true, this thread will cleanup and exit
     *                cleanly.
     */
    public Chore(String name, final int p, final Stoppable stopper) {
      super(name);
      this.sleeper = new Sleeper(p, stopper);
      this.stopper = stopper;
    }
  
    /**
     * @see java.lang.Thread#run()
     */
    @Override public void run() {
      try {
        boolean initialChoreComplete = false;
        while (!this.stopper.isStopped()) {
          long startTime = System.currentTimeMillis();
          try {
            if (!initialChoreComplete) {
              initialChoreComplete = initialChore();
            } else {
              chore();
            }
          } catch (Exception e) {
            LOG.error("Caught exception", e);
            if (this.stopper.isStopped()) {
              continue;
            }
          }
          this.sleeper.sleep(startTime);
        }
      } catch (Throwable t) {
        LOG.error(getName() + "error", t);
      } finally {
        LOG.info(getName() + " exiting");
        cleanup();
      }
    }
  
    /**
     * If the thread is currently sleeping, trigger the core to happen immediately. If it's in the
     * middle of its operation, will begin another operation immediately after finishing this one.
     */
    public void triggerNow() {
      this.sleeper.skipSleepCycle();
    }
  
    /*
     * Exposed for TESTING! calls directly the chore method, from the current thread.
     */
    public void choreForTesting() {
      chore();
    }
  
    /**
     * Override to run a task before we start looping.
     *
     * @return true if initial chore was successful
     */
    protected boolean initialChore() {
      // Default does nothing.
      return true;
    }
  
    /**
     * Look for chores. If any found, do them else just return.
     */
    protected abstract void chore();
  
    /**
     * Sleep for period.
     */
    protected void sleep() {
      this.sleeper.sleep();
    }
  
    /**
     * Called when the chore has completed, allowing subclasses to cleanup any extra overhead
     */
    protected void cleanup() {
    }
  }
  