core/src/main/java/org/apache/hadoop/chukwa/datacollection/adaptor/filetailer/FileTailer.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.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();
      }
    }
  }

}