/*
    * 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.chukwa.datacollection.adaptor.filetailer;
  
  
  import java.util.List;
  import java.util.concurrent.CopyOnWriteArrayList;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.log4j.Logger;
  
  /**
   * A shared thread used by all FileTailingAdaptors.
   * 
   * For now, it tries each file in succession. If it gets through every file
   * within two seconds, and no more data remains, it will sleep.
   * 
   * If there was still data available in any file, the adaptor will loop again.
   * 
   */
  class FileTailer extends Thread {
    static Logger log = Logger.getLogger(FileTailer.class);
  
    private List<LWFTAdaptor> adaptors;
    private volatile boolean isRunning = true;
  //  ChunkQueue eq; // not private -- useful for file tailing adaptor classes
  
    /**
     * How often to tail each file.
     */
    int DEFAULT_SAMPLE_PERIOD_MS = 1000 * 2;
    int SAMPLE_PERIOD_MS = DEFAULT_SAMPLE_PERIOD_MS;
  //  private Configuration conf = null;
    public static final int MAX_SAMPLE_PERIOD = 60 * 1000;
  
    FileTailer(Configuration conf) {
   //   this.conf = conf;
      SAMPLE_PERIOD_MS = conf.getInt(
          "chukwaAgent.adaptor.context.switch.time",
          DEFAULT_SAMPLE_PERIOD_MS);
  //    eq = DataFactory.getInstance().getEventQueue();
  
      // iterations are much more common than adding a new adaptor
      adaptors = new CopyOnWriteArrayList<LWFTAdaptor>();
  
      this.setDaemon(true);
      start();// start the file-tailing thread
    }
  
    // called by FileTailingAdaptor, only
    void startWatchingFile(LWFTAdaptor f) {
      adaptors.add(f);
    }
  
    // called by FileTailingAdaptor, only
    void stopWatchingFile(LWFTAdaptor f) {
      adaptors.remove(f);
    }
  
    public void run() {
      while (isRunning) {
        try {
          boolean shouldISleep = true;
          long startTime = System.currentTimeMillis();
          for (LWFTAdaptor f : adaptors) {
            boolean hasMoreData = f.tailFile();
            shouldISleep &= !hasMoreData;
          }
          long timeToReadFiles = System.currentTimeMillis() - startTime;
          if(timeToReadFiles > MAX_SAMPLE_PERIOD)
            log.warn("took " + timeToReadFiles + " ms to check all files being tailed");
          if (timeToReadFiles < SAMPLE_PERIOD_MS && shouldISleep) {
            Thread.sleep(SAMPLE_PERIOD_MS);
          }
        } catch (Throwable e) {
          log.warn("Exception in FileTailer, while loop", e);
          e.printStackTrace();
        }
      }
    }
  
  }