CoreFx #16274 - LazyInitializer.EnsureInitialized overload for reference types

src/System.Private.CoreLib/src/System/Threading/LazyInitializer.cs

@@ -47,16 +47,8 @@ public static class LazyInitializer
         /// if an object was not used and to then dispose of the object appropriately.
         /// </para>
         /// </remarks>
-        public static T EnsureInitialized<T>(ref T target) where T : class
-        {
-            // Fast path.
-            if (Volatile.Read<T>(ref target) != null)
-            {
-                return target;
-            }
-
-            return EnsureInitializedCore<T>(ref target, LazyHelpers<T>.ActivatorFactorySelectorFunc);
-        }
+        public static T EnsureInitialized<T>(ref T target) where T : class =>
+            Volatile.Read<T>(ref target) ?? EnsureInitializedCore<T>(ref target, LazyHelpers<T>.ActivatorFactorySelectorFunc);
 
         /// <summary>
         /// Initializes a target reference type using the specified function if it has not already been
@@ -86,17 +78,8 @@ public static T EnsureInitialized<T>(ref T target) where T : class
         /// if an object was not used and to then dispose of the object appropriately.
         /// </para>
         /// </remarks>
-        public static T EnsureInitialized<T>(ref T target, Func<T> valueFactory) where T : class
-        {
-            // Fast path.
-            // According to the abstract ECMA CLI memory model, this read should be volatile, due to possible reorderings with
-            // subsequent reads from fields of "target."  However, as of today (7/12/12), Volatile.Read<T> is quite slow, and in practice
-            // this read does *not* need to be volatile, because our memory model preserves ordering of data-dependent reads.
-            if (target != null)
-                return target;
-
-            return EnsureInitializedCore<T>(ref target, valueFactory);
-        }
+        public static T EnsureInitialized<T>(ref T target, Func<T> valueFactory) where T : class =>
+            Volatile.Read(ref target) ?? EnsureInitializedCore<T>(ref target, valueFactory);
 
         /// <summary>
         /// Initialize the target using the given delegate (slow path).
@@ -168,6 +151,29 @@ public static T EnsureInitialized<T>(ref T target, ref bool initialized, ref obj
             return EnsureInitializedCore<T>(ref target, ref initialized, ref syncLock, valueFactory);
         }
 
+        /// <summary>
+        /// Ensure the lock object is intialized.
+        /// </summary>
+        /// <param name="syncLock">A reference to a location containing a mutual exclusive lock. If <paramref name="syncLock"/> is null,
+        /// a new object will be instantiated.</param>
+        /// <returns>Initialized lock object.</returns>
+        private static object EnsureLockInitialized(ref object syncLock) =>
+            syncLock ??
+            Interlocked.CompareExchange(ref syncLock, new object(), null) ??
+            syncLock;
+
+        /// <summary>
+        /// Initializes a target reference type with a specified function if it has not already been initialized.
+        /// </summary>
+        /// <typeparam name="T">The type of the reference to be initialized. Has to be reference type.</typeparam>
+        /// <param name="target">A reference of type <typeparamref name="T"/> to initialize if it has not already been initialized.</param>
+        /// <param name="syncLock">A reference to an object used as the mutually exclusive lock for initializing
+        /// <paramref name="target"/>. If <paramref name="syncLock"/> is null, a new object will be instantiated.</param>
+        /// <param name="valueFactory">The <see cref="T:System.Func{T}"/> invoked to initialize the reference.</param>
+        /// <returns>The initialized value of type <typeparamref name="T"/>.</returns>
+        public static T EnsureInitialized<T>(ref T target, ref object syncLock, Func<T> valueFactory) where T : class =>
+            Volatile.Read(ref target) ?? EnsureInitializedCore<T>(ref target, ref syncLock, valueFactory);
+
         /// <summary>
         /// Ensure the target is initialized and return the value (slow path). This overload permits nulls
         /// and also works for value type targets. Uses the supplied function to create the value.
@@ -183,25 +189,43 @@ public static T EnsureInitialized<T>(ref T target, ref bool initialized, ref obj
         /// <returns>The initialized object.</returns>
         private static T EnsureInitializedCore<T>(ref T target, ref bool initialized, ref object syncLock, Func<T> valueFactory)
         {
-            // Lazily initialize the lock if necessary.
-            object slock = syncLock;
-            if (slock == null)
+            // Lazily initialize the lock if necessary and,  then double check if initialization is still required.
+            lock (EnsureLockInitialized(ref syncLock))
             {
-                object newLock = new object();
-                slock = Interlocked.CompareExchange(ref syncLock, newLock, null);
-                if (slock == null)
+                if (!Volatile.Read(ref initialized))
                 {
-                    slock = newLock;
+                    target = valueFactory();
+                    Volatile.Write(ref initialized, true);
                 }
             }
 
-            // Now double check that initialization is still required.
-            lock (slock)
+            return target;
+        }
+
+        /// <summary>
+        /// Ensure the target is initialized and return the value (slow path). This overload works only for reference type targets.
+        /// Uses the supplied function to create the value.
+        /// </summary>
+        /// <typeparam name="T">The type of target. Has to be reference type.</typeparam>
+        /// <param name="target">A reference to the target to be initialized.</param>
+        /// <param name="syncLock">A reference to a location containing a mutual exclusive lock. If <paramref name="syncLock"/> is null, 
+        /// a new object will be instantiated.</param>
+        /// <param name="valueFactory">
+        /// The <see cref="T:System.Func{T}"/> to invoke in order to produce the lazily-initialized value.
+        /// </param>
+        /// <returns>The initialized object.</returns>
+        private static T EnsureInitializedCore<T>(ref T target, ref object syncLock, Func<T> valueFactory) where T : class
+        {
+            // Lazily initialize the lock if necessary and,  then double check if initialization is still required.
+            lock (EnsureLockInitialized(ref syncLock))
             {
-                if (!Volatile.Read(ref initialized))
+                if (Volatile.Read(ref target) == null)
                 {
-                    target = valueFactory();
-                    Volatile.Write(ref initialized, true);
+                    Volatile.Write(ref target, valueFactory());
+                    if (target == null)
+                    {
+                        throw new InvalidOperationException(SR.Lazy_StaticInit_InvalidOperation);
+                    }
                 }
             }