Add lock to certain "with patch" cases

Switch to --use-threads seems to have broken tests that assumed they could
monkeypatch things. Although that's odd, since while we can have multiple
worker threads, we should never have
parallel tests in the same process.

tests/plugins/tesseract_cache.py

@@ -54,6 +54,7 @@ from functools import partial
 from pathlib import Path
 from subprocess import PIPE, CalledProcessError, CompletedProcess
 from unittest.mock import patch
+import threading
 
 from ocrmypdf import hookimpl
 from ocrmypdf.builtin_plugins.tesseract_ocr import TesseractOcrEngine
@@ -100,7 +101,11 @@ def get_cache_folder(source_pdf, run_args, parsed_args):
 
 def cached_run(options, run_args, **run_kwargs):
     run_args = [str(arg) for arg in run_args]  # flatten PosixPaths
-    args = parser.parse_args(run_args[1:])
+    try:
+        args = parser.parse_args(run_args[1:])
+    except SystemExit:
+        breakpoint()
+        return
 
     if args.imagename in ('stdin', '-'):
         return run(run_args, **run_kwargs)
@@ -176,26 +181,28 @@ def cached_run(options, run_args, **run_kwargs):
 
 
 class CacheOcrEngine(TesseractOcrEngine):
+    lock = threading.Lock()
+
     @staticmethod
     def get_orientation(input_file, options):
-        with patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
-            return TesseractOcrEngine.get_orientation(input_file, options)
+        with CacheOcrEngine.lock, patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
+                return TesseractOcrEngine.get_orientation(input_file, options)
 
     @staticmethod
     def get_deskew(input_file, options) -> float:
-        with patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
+        with CacheOcrEngine.lock, patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
             return TesseractOcrEngine.get_deskew(input_file, options)
 
     @staticmethod
     def generate_hocr(input_file, output_hocr, output_text, options):
-        with patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
+        with CacheOcrEngine.lock, patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
             TesseractOcrEngine.generate_hocr(
                 input_file, output_hocr, output_text, options
             )
 
     @staticmethod
     def generate_pdf(input_file, output_pdf, output_text, options):
-        with patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
+        with CacheOcrEngine.lock, patch('ocrmypdf._exec.tesseract.run', new=partial(cached_run, options)):
             TesseractOcrEngine.generate_pdf(
                 input_file, output_pdf, output_text, options
             )