Introduce a --no-parallel argument

CHANGELOG.rst

@@ -8,6 +8,7 @@ Next version
 
 - Rewrote ``process_imagefields`` to use the multiprocessing module, which
   hopefully improves compatibility on macOS.
+- Introduced a ``--no-parallel`` argument to ``process_imagefields``.
 
 
 0.21 (2024-12-09)

imagefield/management/commands/process_imagefields.py

@@ -25,6 +25,12 @@ def add_arguments(self, parser):
             default="",
             help="Run house-keeping tasks.",
         )
+        parser.add_argument(
+            "--no-parallel",
+            action="store_true",
+            dest="no_parallel",
+            help="Process images sequentially without parallelization.",
+        )
         parser.add_argument(
             "field",
             nargs="*",
@@ -87,18 +93,16 @@ 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"),
         )
 
-        try:
+        if options.get("no_parallel"):
             for index, (instance, errors) in enumerate(
-                pool.imap(fn, queryset.iterator(chunk_size=100))
+                map(fn, queryset.iterator(chunk_size=100))
             ):
                 if errors:
                     self.stderr.write("\n".join(errors))
@@ -112,10 +116,28 @@ def _process_field(self, field, options):
                 # if not done already
                 instance._skip_generate_files = True
                 instance.save()
-
-        finally:
-            pool.close()
-            pool.join()
+        else:
+            pool = mp.Pool()
+            try:
+                for index, (instance, errors) in enumerate(
+                    pool.imap(fn, queryset.iterator(chunk_size=100))
+                ):
+                    if errors:
+                        self.stderr.write("\n".join(errors))
+
+                    progress = "*" * (50 * index // count)
+                    self.stdout.write(
+                        f"\r|{progress.ljust(50)}| {index + 1}/{count}", ending=""
+                    )
+
+                    # Save instance once for good measure; fills in width/height
+                    # if not done already
+                    instance._skip_generate_files = True
+                    instance.save()
+
+            finally:
+                pool.close()
+                pool.join()
 
         self.stdout.write("\r|{}| {}/{}".format("*" * 50, count, count))