Sicherung

Config.Net/Core/LazyVar.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Config.Net.Core
+{
+   /// <summary>
+   /// Implements a lazy value i.e. that can expire in future
+   /// </summary>
+   /// <typeparam name="T"></typeparam>
+   class LazyVar<T> where T : class
+   {
+      private readonly Func<Task<T?>>? _renewFuncAsync;
+      private readonly Func<T?>? _renewFunc;
+      private DateTime _lastRenewed = DateTime.MinValue;
+      private readonly TimeSpan _timeToLive;
+      private T? _value;
+
+      /// <summary>
+      /// Creates an instance of a lazy variable with time-to-live value
+      /// </summary>
+      /// <param name="timeToLive">Time to live. Setting to <see cref="TimeSpan.Zero"/> disables caching completely</param>
+      /// <param name="renewFunc"></param>
+      public LazyVar(TimeSpan timeToLive, Func<Task<T?>> renewFunc)
+      {
+         _timeToLive = timeToLive;
+         _renewFuncAsync = renewFunc ?? throw new ArgumentNullException(nameof(renewFunc));
+         _renewFunc = null;
+      }
+
+      /// <summary>
+      /// Creates an instance of a lazy variable with time-to-live value
+      /// </summary>
+      /// <param name="timeToLive">Time to live. Setting to <see cref="TimeSpan.Zero"/> disables caching completely</param>
+      /// <param name="renewFunc"></param>
+      public LazyVar(TimeSpan timeToLive, Func<T?> renewFunc)
+      {
+         _timeToLive = timeToLive;
+         _renewFuncAsync = null;
+         _renewFunc = renewFunc ?? throw new ArgumentNullException(nameof(renewFunc));
+      }
+
+      /// <summary>
+      /// Gets the values, renewing it if necessary
+      /// </summary>
+      /// <returns>Value</returns>
+      public async Task<T?> GetValueAsync()
+      {
+         if (_renewFuncAsync == null)
+         {
+            throw new InvalidOperationException("cannot renew value, async delegate is not specified");
+         }
+
+         if (_timeToLive == TimeSpan.Zero)
+         {
+            return await _renewFuncAsync();
+         }
+
+         bool expired = (DateTime.UtcNow - _lastRenewed) > _timeToLive;
+
+         if (expired)
+         {
+            _value = await _renewFuncAsync();
+            _lastRenewed = DateTime.UtcNow;
+         }
+
+         return _value;
+      }
+
+      /// <summary>
+      /// Gets the values, renewing it if necessary
+      /// </summary>
+      /// <returns>Value</returns>
+      public T? GetValue()
+      {
+         if (_renewFunc == null)
+         {
+            throw new InvalidOperationException("cannot renew value, synchronous delegate is not specified");
+         }
+
+         if (_timeToLive == TimeSpan.Zero)
+         {
+            return _renewFunc();
+         }
+
+         bool expired = (DateTime.UtcNow - _lastRenewed) > _timeToLive;
+
+         if (expired)
+         {
+            _value = _renewFunc();
+            _lastRenewed = DateTime.UtcNow;
+         }
+
+         return _value;
+      }
+   }
+}