code: def _process_worker(process, process_tile):
      
      logger.debug((process_tile.id, "running on %s" % current_process().name))
  
      # skip execution if overwrite is disabled and tile exists
      if (
          process.config.mode == "continue" and
          process.config.output.tiles_exist(process_tile)
      ):
          logger.debug((process_tile.id, "tile exists, skipping"))
          return ProcessInfo(
              tile=process_tile,
              processed=False,
              process_msg="output already exists",
              written=False,
              write_msg="nothing written"
          )
  
      # execute on process tile
      else:
          with Timer() as t:
              try:
                  output = process.execute(process_tile, raise_nodata=True)
              except MapcheteNodataTile:
                  output = None
          processor_message = "processed in %s" % t
          logger.debug((process_tile.id, processor_message))
          writer_info = process.write(process_tile, output)
          return ProcessInfo(
              tile=process_tile,
              processed=True,
              process_msg=processor_message,
              written=writer_info.written,
              write_msg=writer_info.write_msg
          )
docs: Worker function running the process.