Disable oom killer test for --use-threads

Re: issue Hanging on Random Files  #814

docs/plugins.rst

@@ -152,6 +152,16 @@ hooks. As such, you cannot "chain" a series of plugin filters together in this
 way. Instead, a single hook implementation should be responsible for any such
 chaining operations.
 
+Examples
+========
+
+* OCRmyPDF's test suite contains several plugins that are used to simulate certain
+  test conditions.
+* `ocrmypdf-papermerge <https://github.com/papermerge/OCRmyPDF_papermerge>`_ is
+  a production plugin that integrates OCRmyPDF and the Papermerge document
+  management system.
+
+
 Custom command line arguments
 -----------------------------
 

docs/release_notes.rst

@@ -12,6 +12,13 @@ may be unreliable. Use the API to depend on precise behavior.
 The public API may be useful in scripts that launch OCRmyPDF processes or that
 wish to use some of its features for working with PDFs..
 
+v13.4.1
+=======
+
+-  Temporarily make threads rather than processes the default executor worker, due
+   to a persistent deadlock issue when processes are used. Add a new command line
+   argument ``--no-use-threads`` to disable this.
+
 v13.4.0
 =======
 

src/ocrmypdf/cli.py

@@ -228,7 +228,13 @@ Online documentation is located at:
         help=argparse.SUPPRESS,
     )
     jobcontrol.add_argument(
-        '--use-threads', action='store_true', help=argparse.SUPPRESS
+        '--use-threads', action='store_true', default=True, help=argparse.SUPPRESS
+    )
+    jobcontrol.add_argument(
+        '--no-use-threads',
+        action='store_false',
+        dest='use_threads',
+        help=argparse.SUPPRESS,
     )
 
     metadata = parser.add_argument_group(

src/ocrmypdf/pluginspec.py

@@ -132,6 +132,7 @@ def get_progressbar_class():
     Here is how OCRmyPDF will use the progress bar:
 
     Example:
+
         pbar_class = pm.hook.get_progressbar_class()
         with pbar_class(**tqdm_kwargs) as pbar:
             ...
@@ -235,9 +236,9 @@ def filter_page_image(page: 'PageContext', image_filename: Path) -> Path:
     ``image_filename``. The hook may overwrite ``image_filename`` with a new file.
 
     The output image should preserve the same physical unit dimensions, that is
-    (width * dpi_x, height * dpi_y). That is, if the image is resized, the DPI
+    ``(width * dpi_x, height * dpi_y)``. That is, if the image is resized, the DPI
     must be adjusted by the reciprocal. If this is not preserved, the PDF page
-    will be resized and the OCR layer misaligned. OCRmyPDF does not nothing
+    will be resized and the OCR layer misaligned. OCRmyPDF does nothing
     to enforce these constraints; it is up to the plugin to do sensible things.
 
     OCRmyPDF will create the PDF page based on the image format used (unless the
@@ -399,8 +400,7 @@ def get_ocr_engine() -> OcrEngine:
     """Returns an OcrEngine to use for processing this file.
 
     The OcrEngine may be instantiated multiple times, by both the main process
-    and child process. As such, it must be obtain store any state in ``options``
-    or some common location.
+    and child process.
 
     Note:
         This is a :ref:`firstresult hook<firstresult>`.

tests/test_concurrency.py

@@ -13,6 +13,7 @@ from ocrmypdf import ExitCode
 from .conftest import run_ocrmypdf_api
 
 
+@pytest.mark.skipif(True, reason="--use-threads is currently default")
 @pytest.mark.skipif(os.name == 'nt', reason="Windows doesn't have SIGKILL")
 def test_simulate_oom_killer(resources, no_outpdf):
     exitcode = run_ocrmypdf_api(