def variantcall_batch_region(items):
    """CWL entry point: variant call a batch of samples in a block of regions.
    """
    items = [utils.to_single_data(x) for x in items]
    align_bams = [dd.get_align_bam(x) for x in items]
    variantcaller = _get_batch_variantcaller(items)
    region_blocks = list(set([tuple(x.get("region_block")) for x in items if "region_block" in x]))
    assert len(region_blocks) == 1, region_blocks
    region_block = region_blocks[0]
    # Pre-called input variant files
    if not variantcaller and all(d.get("vrn_file") for d in items):
        return {"vrn_file_region": None, "region_block": region_block}
    caller_fn = get_variantcallers()[variantcaller]
    assoc_files = tz.get_in(("genome_resources", "variation"), items[0], {})
    region = _region_to_coords(region_block[0])
    chrom, start, end = region
    region_str = "_".join(str(x) for x in region)
    batch_name = _get_batch_name(items)
    out_file = os.path.join(dd.get_work_dir(items[0]), variantcaller, chrom,
                            "%s-%s-block.vcf.gz" % (batch_name, region_str))
    utils.safe_makedir(os.path.dirname(out_file))
    with pshared.bedtools_tmpdir(items[0]):
        if variantcaller in SUPPORT_MULTICORE:
            call_file = caller_fn(align_bams, items, dd.get_ref_file(items[0]), assoc_files,
                                  [_region_to_coords(r) for r in region_block], out_file)
        else:
            call_file = _run_variantcall_batch_multicore(items, region_block, out_file)
    return {"vrn_file_region": call_file, "region_block": region_block}