feat: add threaded docling-parse (v6) PDF backend

[cau-git]

Introduces ThreadedDoclingParseDocumentBackend and ThreadedDoclingParsePageBackend as a new PDF backend that drives docling-parse's threaded API directly. The matching StandardPdfPipeline runs page parsing, OCR, layout, table, and assembly in concurrent pipeline stages with a dedicated producer thread.

Backend contract additions:

• PdfPageBackend.page_no abstract property (all existing backends updated: pypdfium2, image, mets-gbs)
• PdfDocumentBackend.iter_pages() default via load_page(); threaded backend overrides to yield in completion order

ThreadedDoclingParseDocumentBackend specifics:

• Constructs one DoclingThreadedPdfParser per instance with fixed decode and render config; no pypdfium2 dependency
• Passes page_numbers=None for the default (all-pages) case; explicit range list only when the caller specifies a finite page_range
• page_count() delegates to parser.page_count(doc_key)
• Coordinate conversion (bottom-left âop-left) applied once in get_segmented_page() and cached; all downstream consumers (layout postprocessor, OCR merge, assembly) receive top-left cells

Pipeline (StandardPdfPipeline / PreprocessThreadedStage):

• Producer thread attaches page backends from iter_pages() to ordered page stubs by page_no, then enqueues ThreadedItems
• Invalid page backends are separated before model calls so they cannot be double-emitted if the preprocessing model raises
• Timeout and early-termination accounting tracks by page-number sets

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

[mergify]

Merge Protections

Your pull request matches the following merge protections and will not be merged until they are valid.

🟢 Enforce conventional commit

Wonderful, this rule succeeded.

Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?(!)?:

[github-actions]

✅ DCO Check Passed

Thanks @cau-git, all your commits are properly signed off. 🎉

[PeterStaar-IBM]

lgtm!

[codecov]

Codecov Report

❌ Patch coverage is 75.65543% with 65 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling/backend/docling_parse_backend.py	75.00%	30 Missing ⚠️
docling/pipeline/standard_pdf_pipeline.py	79.34%	19 Missing ⚠️
...erimental/pipeline/threaded_layout_vlm_pipeline.py	0.00%	6 Missing ⚠️
docling/pipeline/extraction_vlm_pipeline.py	28.57%	5 Missing ⚠️
docling/pipeline/vlm_pipeline.py	40.00%	3 Missing ⚠️
docling/backend/mets_gbs_backend.py	83.33%	1 Missing ⚠️
docling/backend/pdf_backend.py	90.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[dosubot]

Related Knowledge

1 document with suggested updates is ready for review.

Docling

What are the detailed pipeline options and processing behaviors for PDF, DOCX, PPTX, and XLSX files in the Python SDK?

View Suggested Changes

@@ -4,6 +4,9 @@
     - `from_formats`: Supported input formats include `docx`, `pptx`, `html`, `image`, `pdf`, `asciidoc`, `md` (including `txt`, `text`, `qmd`, `rmd`), `csv`, `xlsx`, `xml_uspto`, `xml_jats`, `xml_xbrl`, `mets_gbs`, `json_docling`, `audio`, `vtt`, `latex`
     - `to_formats`: Supported output formats include `md`, `json`, `yaml`, `html`, `html_split_page`, `text`, `doctags`, `vtt`
     - `pdf_backend`: Allowed values: `pypdfium2`, `docling_parse`, `dlparse_v1`, `dlparse_v2`, `dlparse_v4` (default: `docling_parse`)
+          - `threaded_docling_parse`: Threaded Docling Parse backend optimized for concurrent page parsing in the standard PDF pipeline
+      - Backend-specific options:
+          - For `threaded_docling_parse`: `parser_threads` (Optional[PositiveInt]): Number of parser threads to use for the threaded docling-parse backend. If unset, the backend falls back to global accelerator thread settings
     - `do_ocr` (default True): Use OCR
     - `force_ocr`: Replace existing text with OCR-generated text
     - `ocr_engine`, `ocr_lang`: OCR engine and language options

[Accept] [Edit] [Decline]

^{How did I do? Any feedback?}