protected final void createSingleThreadPoolConsumeExecutor(String walType, final Path rootDir,
    final String prefix) {
    ThreadPoolExecutor threadPool =
      new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>(),
        new ThreadFactoryBuilder().setNameFormat(walType + "-%d-" + rootDir.toString() + "-prefix:"
          + (prefix == null ? "default" : prefix).replace("%", "%%")).setDaemon(true).build());
    hasConsumerTask = () -> threadPool.getQueue().peek() == consumer;
    consumeExecutor = threadPool;
    this.shouldShutDownConsumeExecutorWhenClose = true;
  }
A log file has a creation timestamp (in ms) in its file name ({@link #filenum}. This helper
method returns the creation timestamp from a given log file. It extracts the timestamp assuming
the filename is created with the {@link #computeFilename(long filenum)} method.
@return timestamp, as in the log file name.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AbstractFSWAL.java