Add threading lock

app/routes/api_v1/endpoints/courses.py

+from threading import Lock
 from typing import List
 
 from cachetools import TTLCache, cached
@@ -11,9 +12,11 @@ router = APIRouter()
 
 
 @router.get("/search", response_model=List[schemas.CourseWithoutAppointments])
-def list_and_search_courses_by_name(semesterId: int = Query(..., example=1),
+def list_and_search_courses_by_name(
+    semesterId: int = Query(..., example=1),
     title: str = Query(..., example="Systemsoftware und"),
-                                    broker: DatabaseBroker = Depends(get_database_broker)):
+    broker: DatabaseBroker = Depends(get_database_broker),
+):
     """
     List and search courses by name.
     """
@@ -21,19 +24,31 @@ def list_and_search_courses_by_name(semesterId: int = Query(..., example=1),
 
 
 @router.get("/all", response_model=List[schemas.CourseWithoutAppointments])
-@cached(cache=TTLCache(maxsize=1024, ttl=600), key=lambda semesterId, broker: semesterId)
-def list_all_courses_of_semester(semesterId: int = Query(..., example=1),
-                                 broker: DatabaseBroker = Depends(get_database_broker)):
+@cached(
+    cache=TTLCache(maxsize=1024, ttl=600),
+    key=lambda semesterId, broker: semesterId,
+    lock=Lock(),
+)
+def list_all_courses_of_semester(
+    semesterId: int = Query(..., example=1),
+    broker: DatabaseBroker = Depends(get_database_broker),
+):
     """
     List all courses of a semester.
     """
     return broker.get_all_courses_of_semester(semesterId)
 
 
-@router.get("/{courseId}", response_model=schemas.Course, responses={404: {"model": schemas.DetailMessage}})
-def retrieve_information_of_a_course(semesterId: int = Query(..., example=1),
+@router.get(
+    "/{courseId}",
+    response_model=schemas.Course,
+    responses={404: {"model": schemas.DetailMessage}},
+)
+def retrieve_information_of_a_course(
+    semesterId: int = Query(..., example=1),
     courseId: str = Path(..., example="L.079.05401"),
-                                     broker: DatabaseBroker = Depends(get_database_broker)):
+    broker: DatabaseBroker = Depends(get_database_broker),
+):
     """
     Querries course by id with all small groups and appointments.
     """