update caching to use automatic timer instead of request based to prevent task cancellation

Data/Helpers/DataValueCache.cs

@@ -1,58 +1,83 @@
 using System;
-using System.Collections.Generic;
+using System.Collections.Concurrent;
 using System.Threading;
 using System.Threading.Tasks;
 using Data.Abstractions;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
+using Timer = System.Timers.Timer;
 
 namespace Data.Helpers
 {
-    public class DataValueCache<T, V> : IDataValueCache<T, V> where T : class
+    public class DataValueCache<TEntityType, TReturnType> : IDataValueCache<TEntityType, TReturnType>
+        where TEntityType : class
     {
         private readonly ILogger _logger;
         private readonly IDatabaseContextFactory _contextFactory;
-        private readonly Dictionary<string, CacheState> _cacheStates = new Dictionary<string, CacheState>();
+
+        private readonly ConcurrentDictionary<string, CacheState> _cacheStates =
+            new ConcurrentDictionary<string, CacheState>();
+
+        private bool _autoRefresh;
         private const int DefaultExpireMinutes = 15;
+        private Timer _timer;
 
         private class CacheState
         {
             public string Key { get; set; }
             public DateTime LastRetrieval { get; set; }
             public TimeSpan ExpirationTime { get; set; }
-            public Func<DbSet<T>, CancellationToken, Task<V>> Getter { get; set; }
-            public V Value { get; set; }
+            public Func<DbSet<TEntityType>, CancellationToken, Task<TReturnType>> Getter { get; set; }
+            public TReturnType Value { get; set; }
 
             public bool IsExpired => ExpirationTime != TimeSpan.MaxValue &&
                                      (DateTime.Now - LastRetrieval.Add(ExpirationTime)).TotalSeconds > 0;
         }
 
-        public DataValueCache(ILogger<DataValueCache<T, V>> logger, IDatabaseContextFactory contextFactory)
+        public DataValueCache(ILogger<DataValueCache<TEntityType, TReturnType>> logger,
+            IDatabaseContextFactory contextFactory)
         {
             _logger = logger;
             _contextFactory = contextFactory;
         }
 
-        public void SetCacheItem(Func<DbSet<T>, CancellationToken, Task<V>> getter, string key,
-            TimeSpan? expirationTime = null)
+        ~DataValueCache()
+        {
+            _timer?.Stop();
+            _timer?.Dispose();
+        }
+
+        public void SetCacheItem(Func<DbSet<TEntityType>, CancellationToken, Task<TReturnType>> getter, string key,
+            TimeSpan? expirationTime = null, bool autoRefresh = false)
         {
             if (_cacheStates.ContainsKey(key))
             {
-                _logger.LogDebug("Cache key {key} is already added", key);
+                _logger.LogDebug("Cache key {Key} is already added", key);
                 return;
             }
 
-            var state = new CacheState()
+            var state = new CacheState
             {
                 Key = key,
                 Getter = getter,
                 ExpirationTime = expirationTime ?? TimeSpan.FromMinutes(DefaultExpireMinutes)
             };
 
-            _cacheStates.Add(key, state);
+            _autoRefresh = autoRefresh;
+
+            _cacheStates.TryAdd(key, state);
+
+            if (!_autoRefresh || expirationTime == TimeSpan.MaxValue)
+            {
+                return;
+            }
+
+            _timer = new Timer(state.ExpirationTime.TotalMilliseconds);
+            _timer.Elapsed += async (sender, args) => await RunCacheUpdate(state, CancellationToken.None);
+            _timer.Start();
         }
 
-        public async Task<V> GetCacheItem(string keyName, CancellationToken cancellationToken = default)
+        public async Task<TReturnType> GetCacheItem(string keyName, CancellationToken cancellationToken = default)
         {
             if (!_cacheStates.ContainsKey(keyName))
             {
@@ -61,7 +86,9 @@ namespace Data.Helpers
 
             var state = _cacheStates[keyName];
 
-            if (state.IsExpired || state.Value == null)
+            // when auto refresh is off we want to check the expiration and value
+            // when auto refresh is on, we want to only check the value, because it'll be refreshed automatically
+            if ((state.IsExpired || state.Value == null) && !_autoRefresh || _autoRefresh && state.Value == null)
             {
                 await RunCacheUpdate(state, cancellationToken);
             }
@@ -73,15 +100,16 @@ namespace Data.Helpers
         {
             try
             {
+                _logger.LogDebug("Running update for {ClassName} {@State}", GetType().Name, state);
                 await using var context = _contextFactory.CreateContext(false);
-                var set = context.Set<T>();
+                var set = context.Set<TEntityType>();
                 var value = await state.Getter(set, token);
                 state.Value = value;
                 state.LastRetrieval = DateTime.Now;
             }
             catch (Exception ex)
             {
-                _logger.LogError(ex, "Could not get cached value for {key}", state.Key);
+                _logger.LogError(ex, "Could not get cached value for {Key}", state.Key);
             }
         }
     }