Initial push to use ILive in import process

osu.Game/Database/ILive.cs

@@ -0,0 +1,42 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+
+namespace osu.Game.Database
+{
+    /// <summary>
+    /// A wrapper to provide access to database backed classes in a thread-safe manner.
+    /// </summary>
+    /// <typeparam name="T">The databased type.</typeparam>
+    public interface ILive<out T> where T : class
+    {
+        Guid ID { get; }
+
+        /// <summary>
+        /// Perform a read operation on this live object.
+        /// </summary>
+        /// <param name="perform">The action to perform.</param>
+        void PerformRead(Action<T> perform);
+
+        /// <summary>
+        /// Perform a read operation on this live object.
+        /// </summary>
+        /// <param name="perform">The action to perform.</param>
+        TReturn PerformRead<TReturn>(Func<T, TReturn> perform);
+
+        /// <summary>
+        /// Perform a write operation on this live object.
+        /// </summary>
+        /// <param name="perform">The action to perform.</param>
+        void PerformWrite(Action<T> perform);
+
+        /// <summary>
+        /// Resolve the value of this instance on the current thread's context.
+        /// </summary>
+        /// <remarks>
+        /// After resolving the data should not be passed between threads.
+        /// </remarks>
+        T Value { get; }
+    }
+}