thread safety for background service

AccessQueueService/Services/AccessCleanupBackgroundService.cs

@@ -17,7 +17,7 @@ namespace AccessQueueService.Services
             var cleanupIntervalMillis = _config.GetValue<int>("AccessQueue:CleanupIntervalSeconds") * 1000;
             while (!stoppingToken.IsCancellationRequested)
             {
-                _accessService.DeleteExpiredTickets();
+                await _accessService.DeleteExpiredTickets();
                 await Task.Delay(cleanupIntervalMillis, stoppingToken);
             }
         }

AccessQueueService/Services/AccessService.cs

@@ -1,4 +1,5 @@
-using AccessQueueService.Data;
+using System.Threading.Tasks;
+using AccessQueueService.Data;
 using AccessQueueService.Models;
 
 namespace AccessQueueService.Services
@@ -106,6 +107,17 @@ namespace AccessQueueService.Services
             }
         }
 
-        public int DeleteExpiredTickets() => _accessQueueRepo.DeleteExpiredTickets();
+        public async Task<int> DeleteExpiredTickets()
+        {
+            await _queueLock.WaitAsync();
+            try
+            {
+                return _accessQueueRepo.DeleteExpiredTickets();
+            }
+            finally
+            {
+                _queueLock.Release();
+            }
+        }
     }
 }

AccessQueueService/Services/IAccessService.cs

@@ -6,6 +6,6 @@ namespace AccessQueueService.Services
     {
         public Task<AccessResponse> RequestAccess(string userId);
         public Task<bool> RevokeAccess(string userId);
-        public int DeleteExpiredTickets();
+        public Task<int> DeleteExpiredTickets();
     }
 }