private boolean handleWALEntry(WALEntry walEntry) {
      if (walEntry.isSignal()) {
        return handleSignalEntry((WALSignalEntry) walEntry);
      }

      handleInfoEntry(walEntry);
      return false;
    }
Handle wal info and signal entry.

@return true if fsyncWorkingBuffer has been called, which means this serialization task
    should be ended.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/dataregion/wal/buffer/WALBuffer.java