Rewrite the code to use multiprocessing

Author: matthiask

CHANGELOG.rst

@@ -6,6 +6,9 @@ Change log
 Next version
 ~~~~~~~~~~~~
 
+- Rewrote ``process_imagefields`` to use the multiprocessing module, which
+  hopefully improves compatibility on macOS.
+
 
 0.21 (2024-12-09)
 ~~~~~~~~~~~~~~~~~

imagefield/management/commands/process_imagefields.py

@@ -1,5 +1,5 @@
+import multiprocessing as mp
 import sys
-from concurrent.futures import ProcessPoolExecutor
 from fnmatch import fnmatch
 from functools import partial
 
@@ -87,16 +87,18 @@ def _process_field(self, field, options):
                 force=options.get("force"),
             )
 
+        pool = mp.Pool()
+
         fn = partial(
             _process_instance,
             field=field,
             housekeep=options.get("housekeep"),
             force=options.get("force"),
         )
 
-        with ProcessPoolExecutor() as executor:
+        try:
             for index, (instance, errors) in enumerate(
-                executor.map(fn, queryset.iterator(chunk_size=100))
+                pool.imap(fn, queryset.iterator(chunk_size=100))
             ):
                 if errors:
                     self.stderr.write("\n".join(errors))
@@ -111,6 +113,10 @@ def _process_field(self, field, options):
                 instance._skip_generate_files = True
                 instance.save()
 
+        finally:
+            pool.close()
+            pool.join()
+
         self.stdout.write("\r|{}| {}/{}".format("*" * 50, count, count))