Offload initial email task (#8413)

- Prevent blocking on email task
- Allow worker to try multiple times
- Don't pass 500 error back to form validation

src/backend/InvenTree/InvenTree/serializers.py

@@ -510,6 +510,7 @@ class UserCreateSerializer(ExtendedUserSerializer):
     def create(self, validated_data):
         """Send an e email to the user after creation."""
         from InvenTree.helpers_model import get_base_url
+        from InvenTree.tasks import email_user, offload_task
 
         base_url = get_base_url()
 
@@ -527,8 +528,12 @@ class UserCreateSerializer(ExtendedUserSerializer):
         if base_url:
             message += f'\n\nURL: {base_url}'
 
+        subject = _('Welcome to InvenTree')
+
         # Send the user an onboarding email (from current site)
-        instance.email_user(subject=_('Welcome to InvenTree'), message=message)
+        offload_task(
+            email_user, instance.pk, str(subject), str(message), force_async=True
+        )
 
         return instance
 

src/backend/InvenTree/InvenTree/tasks.py

@@ -12,6 +12,7 @@ from datetime import datetime, timedelta
 from typing import Callable, Optional
 
 from django.conf import settings
+from django.contrib.auth import get_user_model
 from django.core.exceptions import AppRegistryNotReady
 from django.core.management import call_command
 from django.db import DEFAULT_DB_ALIAS, connections
@@ -693,3 +694,14 @@ def check_for_migrations(force: bool = False, reload_registry: bool = True):
         # We should be current now - triggering full reload to make sure all models
         # are loaded fully in their new state.
         registry.reload_plugins(full_reload=True, force_reload=True, collect=True)
+
+
+def email_user(user_id: int, subject: str, message: str) -> None:
+    """Send a message to a user."""
+    try:
+        user = get_user_model().objects.get(pk=user_id)
+    except Exception:
+        logger.warning('User <%s> not found - cannot send welcome message', user_id)
+        return
+
+    user.email_user(subject=subject, message=message)