@Override
      public Void call() throws Exception {
        if (rollWriterLock.tryLock(walShutdownTimeout, TimeUnit.SECONDS)) {
          try {
            doShutdown();
            if (syncFutureCache != null) {
              syncFutureCache.clear();
            }
          } finally {
            rollWriterLock.unlock();
          }
        } else {
          throw new IOException("Waiting for rollWriterLock timeout");
        }
        return null;
      }
Get the backing files associated with this WAL.
@return may be null if there are no files.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AbstractFSWAL.java