default loading to single thread to avoid multithread overhead

import numpy as np

import param

import tifffile

from tqdm.auto import tqdm

from tqdm.contrib.concurrent import process_map

# standard imports

    dc_fnmatch = param.String(default="*", doc="fnmatch for selecting dc files from dc_dir")

    # NOTE: 0 means use as many as possible

    max_workers = param.Integer(

        default=0,

        default=1,  # default to single process

        bounds=(0, None),

        doc="Maximum number of processes allowed during loading",

    )

    # figure out the file type and select corresponding reader from dxchange

    file_ext = Path(filelist[0]).suffix.lower()

    if file_ext in (".tif", ".tiff"):

        # reader = dxchange.read_tiff

        # NOTE: switch to tifffile until we figure out what is causing dxchange

        #       to slow down the loading speed.

        reader = tifffile.imread

        # use tifffile directly for a faster loading

        reader = partial(tifffile.imread, out="memmap")

    elif file_ext == ".fits":

        reader = dxchange.read_fits

    else:

        logger.error(f"Unsupported file type: {file_ext}")

        raise ValueError("Unsupported file type.")

    # read the data into numpy array via map_process

    # NOTE: For regular dataset, single thread reading is actually faster

    #       as the overhead of multiprocessing will overshadow the benefits.

    if max_workers == 1:

        progress_bar = tqdm if tqdm_class is None else tqdm_class

        # single thread reading

        rst = [_forgiving_reader(f, reader) for f in progress_bar(filelist, desc=desc)]

    else:

        # multi-thread reading

        # NOTE: the benefits of multi-threading is only visible when

        #       - the file list is really long

        #       - there are a lot of cores available

        kwargs = {

            "max_workers": max_workers,

            "desc": desc,

        }

    if tqdm_class:

        kwargs["tqdm_class"] = tqdm_class

        rst = process_map(partial(_forgiving_reader, reader=reader), filelist, **kwargs)

    # return the results

    # NOTE: there is no need to convert to float at this point, and it will save

    #       a lot of memory and time if the conversion is done after cropping.