Skip ready functions if not in main thread or plugins are not loaded yet (#5005)

* Skip ready functions if not in main thread or plugins are not loaded yet

* Debug integration tests

* Update ready.py

* Update ready.py

* Fix isInMainThread and isPluginRegistryLoaded ready functions

* Preload gunicorn app to only invoke the appconfig ready functions once

* debug: test prints for statistics

* Remove debug print

* Test without

* Revert "Test without"

This reverts commit 1bc1872893.

* Second test

* Add checks back to part, label, user model

* Add checks back to inventree, plugin apps

* log server output for debugging

* hopefully I can get the log this time+

* Next test

* Test with --noreload

* Next test

* trigger: ci, because session expired

* block the second ready execution instead of the first

* fix: load order

* Fix test and revert gh actions workflow change

* Added all_apps method to reload machanism

* Changed detect reload mechanism

* Also trigger ready on reload

* Add skipping second reload back for testing mode

* Added doc string back

* Update InvenTree/plugin/base/integration/AppMixin.py

InvenTree/plugin/apps.py

@@ -10,7 +10,7 @@ from django.apps import AppConfig
 
 from maintenance_mode.core import set_maintenance_mode
 
-from InvenTree.ready import canAppAccessDatabase
+from InvenTree.ready import canAppAccessDatabase, isInMainThread
 from plugin import registry
 
 logger = logging.getLogger('inventree')
@@ -23,6 +23,10 @@ class PluginAppConfig(AppConfig):
 
     def ready(self):
         """The ready method is extended to initialize plugins."""
+        # skip loading if we run in a background thread
+        if not isInMainThread():
+            return
+
         if not canAppAccessDatabase(allow_test=True, allow_plugins=True):
             logger.info("Skipping plugin loading sequence")  # pragma: no cover
         else: