Locking the element on take_snapshot to avoid racing condition issues

requirements.txt

@@ -30,6 +30,7 @@ django-ipware==0.1.0
 premailer==2.8.1
 django-transactional-cleanup==0.1.13
 lxml==3.4.1
+git+https://github.com/Xof/django-pglocks.git@dbb8d7375066859f897604132bd437832d2014ea
 
 # Comment it if you are using python >= 3.4
 enum34==1.0

taiga/projects/history/services.py

@@ -37,6 +37,7 @@ from django.contrib.contenttypes.models import ContentType
 from django.core.paginator import Paginator, InvalidPage
 from django.apps import apps
 from django.db import transaction as tx
+from django_pglocks import advisory_lock
 
 from taiga.mdrender.service import render as mdrender
 from taiga.base.utils.db import get_typename_for_model_class
@@ -269,6 +270,7 @@ def get_modified_fields(obj:object, last_modifications):
 
     return modified_fields
 
+
 @tx.atomic
 def take_snapshot(obj:object, *, comment:str="", user=None, delete:bool=False):
     """
@@ -280,6 +282,7 @@ def take_snapshot(obj:object, *, comment:str="", user=None, delete:bool=False):
     """
 
     key = make_key_from_model_object(obj)
+    with advisory_lock(key) as acquired_key_lock:
         typename = get_typename_for_model_class(obj.__class__)
 
         new_fobj = freeze_model_instance(obj)