protected final void setWaitOnShutdownInSeconds(int waitOnShutdownInSeconds,
    String waitOnShutdownInSecondsConfigKey) {
    this.waitOnShutdownInSeconds = waitOnShutdownInSeconds;
    this.waitOnShutdownInSecondsConfigKey = waitOnShutdownInSecondsConfigKey;
  }
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