From 9d50f0d1c9f2d4e81791efbe7d03f0377feef7d7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=A4=D1=80=D0=BE=D0=BB=D0=BE=D0=B2?=
 <nikita.grigorevich@gmail.com>
Date: Fri, 20 Aug 2021 12:45:26 +0500
Subject: [PATCH] fix add SemaphoreSlim into Cache.Refresh(..) and
 Cache.RefreshAsync(..) method to avoid racing

---
 AsbCloudInfrastructure/Services/Cache/CacheTable.cs | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/AsbCloudInfrastructure/Services/Cache/CacheTable.cs b/AsbCloudInfrastructure/Services/Cache/CacheTable.cs
index db0aee2e..445fb8cc 100644
--- a/AsbCloudInfrastructure/Services/Cache/CacheTable.cs
+++ b/AsbCloudInfrastructure/Services/Cache/CacheTable.cs
@@ -13,6 +13,7 @@ namespace AsbCloudInfrastructure.Services.Cache
         private (DateTime refreshDate, IEnumerable<object> entities) data;
         private readonly List<TEntity> cached;
         private readonly DbSet<TEntity> dbSet;
+        private readonly SemaphoreSlim semaphore = new SemaphoreSlim(1, 1);
 
         internal CacheTable(DbContext context, (DateTime refreshDate, IEnumerable<object> entities) data)
         {
@@ -27,7 +28,10 @@ namespace AsbCloudInfrastructure.Services.Cache
         public int Refresh()
         {
             if (cached.Any())
+            {
+                semaphore.Wait();
                 cached.Clear();
+            }
             var dbEntities = context.Set<TEntity>().AsNoTracking().ToList();
             cached.AddRange(dbEntities);
             data.refreshDate = DateTime.Now;
@@ -37,7 +41,10 @@ namespace AsbCloudInfrastructure.Services.Cache
         public async Task<int> RefreshAsync(CancellationToken token = default)
         {
             if (cached.Any())
-                cached.Clear();
+            {
+                await semaphore.WaitAsync(token).ConfigureAwait(true);
+                cached.Clear(); 
+            }
             var dbEntities = await context.Set<TEntity>().AsNoTracking().ToListAsync(token).ConfigureAwait(false);
             cached.AddRange(dbEntities);
             data.refreshDate = DateTime.Now;