Fixing threading._RLock exception on Python 3.6

Issue was the usual business: objects that cross process boundaries need
to be picklable and Python 3.6 is more strict about this. The logger
object in particular interfered, so now we suppress it and rebuild it
in process.

src/ocrmypdf/_jobcontext.py

@@ -22,10 +22,29 @@ import os
 from contextlib import suppress
 
 
-class PDFContext:
+class PicklableLoggerMixin:
+    def __init__(self):
+        self._log = None
+
+    @property
+    def log(self):
+        if not self._log:
+            self._log = self.get_logger()
+        return self._log
+
+    def __getstate__(self):
+        log = self._log
+        self._log = None
+        state = self.__dict__
+        self._log = log
+        return state
+
+
+class PDFContext(PicklableLoggerMixin):
     """Holds our context for a particular run of the pipeline"""
 
     def __init__(self, options, work_folder, origin, pdfinfo):
+        PicklableLoggerMixin.__init__(self)
         self.options = options
         self.work_folder = work_folder
         self.origin = origin
@@ -36,7 +55,9 @@ class PDFContext:
             self.name = 'origin.pdf'
         if self.name == '-':
             self.name = 'stdin'
-        self.log = get_logger(options, filename=self.name)
+
+    def get_logger(self):
+        return make_logger(self.options, filename=self.name)
 
     def get_path(self, name):
         return os.path.join(self.work_folder, name)
@@ -47,22 +68,27 @@ class PDFContext:
             yield PageContext(self, n)
 
 
-class PageContext:
-    """Holds our context for a page"""
+class PageContext(PicklableLoggerMixin):
+    """Holds our context for a page
+
+    Must be pickable, so only store intrinsic/simple data elements
+    """
 
     def __init__(self, pdf_context, pageno):
-        self.pdf_context = pdf_context
+        PicklableLoggerMixin.__init__(self)
+        self.work_folder = pdf_context.work_folder
+        self.origin = pdf_context.origin
         self.options = pdf_context.options
+        self.name = pdf_context.name
         self.pageno = pageno
         self.pageinfo = pdf_context.pdfinfo[pageno]
-        self.log = get_logger(
-            pdf_context.options, filename=self.pdf_context.name, page=(self.pageno + 1)
-        )
+        self._log = None
+
+    def get_logger(self):
+        return make_logger(self.options, filename=self.name, page=self.pageno + 1)
 
     def get_path(self, name):
-        return os.path.join(
-            self.pdf_context.work_folder, "%06d_%s" % (self.pageno + 1, name)
-        )
+        return os.path.join(self.work_folder, "%06d_%s" % (self.pageno + 1, name))
 
 
 def cleanup_working_files(work_folder, options):
@@ -88,7 +114,7 @@ class LogNamePageAdapter(logging.LoggerAdapter):
         )
 
 
-def get_logger(options=None, prefix='ocrmypdf', filename=None, page=None):
+def make_logger(options=None, prefix='ocrmypdf', filename=None, page=None):
     log = logging.getLogger(prefix)
     if filename and page:
         adapter = LogNamePageAdapter(log, dict(filename=filename, page=page))

src/ocrmypdf/_sync.py

@@ -29,7 +29,7 @@ from tempfile import mkdtemp
 from tqdm import tqdm
 
 from . import VERSION
-from ._jobcontext import PDFContext, cleanup_working_files, get_logger
+from ._jobcontext import PDFContext, cleanup_working_files, make_logger
 from ._pipeline import (
     convert_to_pdfa,
     copy_final,
@@ -83,17 +83,13 @@ def exec_page_sync(page_context):
     if is_ocr_required(page_context):
         if options.rotate_pages:
             # Rasterize
-            rasterize_preview_out = rasterize_preview(
-                page_context.pdf_context.origin, page_context
-            )
+            rasterize_preview_out = rasterize_preview(page_context.origin, page_context)
             orientation_correction = get_orientation_correction(
                 rasterize_preview_out, page_context
             )
 
         rasterize_out = rasterize(
-            page_context.pdf_context.origin,
-            page_context,
-            correction=orientation_correction,
+            page_context.origin, page_context, correction=orientation_correction
         )
 
         preprocess_out = rasterize_out
@@ -240,7 +236,7 @@ def exec_concurrent(context):
 
 
 def run_pipeline(options):
-    log = get_logger(options, __name__)
+    log = make_logger(options, __name__)
     log.debug('ocrmypdf ' + VERSION)
 
     result = check_options(options)