Make Barrel and HttpCache singletons thread-safe

src/MonkeyCache.FileStore/Barrel.cs

@@ -47,12 +47,12 @@ public class Barrel : IBarrel
 
 		public bool AutoExpire { get ; set; }
 
-		static Barrel instance = null;
+		static readonly Lazy<Barrel> instance = new Lazy<Barrel>(() => new Barrel());
 
 		/// <summary>
 		/// Gets the instance of the Barrel
 		/// </summary>
-		public static IBarrel Current => (instance ?? (instance = new Barrel()));
+		public static IBarrel Current => instance.Value;
 
 		/// <summary>
 		/// FileStore Barrel

src/MonkeyCache.LiteDB/Barrel.cs

@@ -29,22 +29,22 @@ public class Barrel : IBarrel
 
 		public bool AutoExpire { get; set; }
 
-		static Barrel instance = null;
+		static Lazy<Barrel> instance = new Lazy<Barrel>(() => new Barrel());
 		static ILiteCollection<Banana> col;
 
 		/// <summary>
 		/// Gets the instance of the Barrel
 		/// </summary>
-		public static IBarrel Current => (instance ?? (instance = new Barrel()));
+		public static IBarrel Current => instance.Value;
 
 		public static IBarrel Create(string cacheDirectory, bool cache = false)
 		{
 			if (!cache)
 				return new Barrel(cacheDirectory);
 
-			if(instance == null)
-				instance = new Barrel(cacheDirectory);
-			return instance;
+			if(!instance.IsValueCreated)
+				instance = new Lazy<Barrel>(() => new Barrel(cacheDirectory));
+			return instance.Value;
 		}
 
 		Barrel(string cacheDirectory = null)

src/MonkeyCache.SQLite/Barrel.cs

@@ -27,12 +27,12 @@ public class Barrel : IBarrel
 
 		public bool AutoExpire { get; set; }
 
-		static Barrel instance = null;
+		static readonly Lazy<Barrel> instance = new Lazy<Barrel>(() => new Barrel());
 
 		/// <summary>
 		/// Gets the instance of the Barrel
 		/// </summary>
-		public static IBarrel Current => (instance ?? (instance = new Barrel()));
+		public static IBarrel Current => instance.Value;
 
 		public static IBarrel Create(string cacheDirectory)
 			=> new Barrel(cacheDirectory);
@@ -320,4 +320,4 @@ public void Empty(params string[] key)
 
 		#endregion
 	}
-}
+}

src/MonkeyCache/HttpCache.cs

@@ -13,12 +13,12 @@ namespace MonkeyCache
 	public class HttpCache
 	{
 
-		static HttpCache instance = null;
+		static readonly Lazy<HttpCache> instance = new Lazy<HttpCache>(() => new HttpCache());
 
 		/// <summary>
 		/// Gets the instance of the HttpCache
 		/// </summary>
-		public static HttpCache Current => (instance ?? (instance = new HttpCache()));
+		public static HttpCache Current => instance.Value;
 
 		HttpCache()
 		{