public void init(StoreScanner sourceScanner, WriterFactory factory) {
    this.writerFactory = factory;
    this.sourceScanner = sourceScanner;
  }
Initializes multi-writer before usage.
@param sourceScanner Optional store scanner to obtain the information about read progress.
@param factory       Factory used to produce individual file writers.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/AbstractMultiFileWriter.java