package com.github.triceo.splitlog;
   
   import java.util.concurrent.ScheduledExecutorService;
   
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import com.github.triceo.splitlog.api.Follower;
   
  /**
   * As followers are terminated via {@link #stopFollowing(Follower)} and then
   * discarded by GC, some messages will become unreachable. (No followers point
   * to them any longer.)
   *
   * The point of this class is to review the situation and discard whatever
   * messages are no longer reachable. Otherwise they'd be uselessly occupying
   * memory.
   *
   * This class is intended to be run periodically by
   * {@link ScheduledExecutorService}.
   */
  final class LogWatchStorageSweeper implements Runnable {
  
      private static final Logger LOGGER = LoggerFactory.getLogger(LogWatchStorageSweeper.class);
      private final LogWatchStorageManager toSweep;
  
      public LogWatchStorageSweeper(final LogWatchStorageManager watch) {
          this.toSweep = watch;
      }
  
      @Override
      public void run() {
          final MessageStore messages = this.toSweep.getMessageStore();
          final int minId = this.toSweep.getFirstReachableMessageId();
          LogWatchStorageSweeper.LOGGER.debug(
                  "Starting message sweep from {}. First reachable message ID reportedly {}.",
                  this.toSweep.getLogWatch(), minId);
          if (minId < 0) {
              LogWatchStorageSweeper.LOGGER.info("Sweeping all messages from {} as none are reachable.",
                      this.toSweep.getLogWatch());
              messages.discardBefore(messages.getNextPosition());
              return;
          } else if (messages.isEmpty()) {
              LogWatchStorageSweeper.LOGGER.info("No messages in {}.", this.toSweep.getLogWatch());
              return;
          }
          final int num = messages.discardBefore(minId);
          LogWatchStorageSweeper.LOGGER.info("Swept {} messages from {}.", num, this.toSweep.getLogWatch());
      }
  
  }