Initial data commit

Task/Singleton/C-sharp/singleton-2.cs

@@ -0,0 +1,18 @@
+public sealed class Singleton2 //Lazy: Yes ||| Thread-safe: Yes ||| Uses locking: Yes, but only once
+{
+    private static Singleton2 instance;
+    private static readonly object lockObj = new object();
+
+    public static Singleton2 Instance {
+        get {
+            if (instance == null) {
+                lock(lockObj) {
+                    if (instance == null) {
+                        instance = new Singleton2();
+                    }
+                }
+            }
+            return instance;
+        }
+    }
+}