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//
// LazyInitializer.cs
//
// Authors:
// Jérémie "Garuma" Laval <jeremie.laval@gmail.com>
// Marek Safar (marek.safar@gmail.com)
//
// Copyright (c) 2009 Jérémie "Garuma" Laval
// Copyright 2011 Xamarin, Inc (http://www.xamarin.com)
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#if NET_4_0
namespace System.Threading
{
public static class LazyInitializer
{
public static T EnsureInitialized<T> (ref T target) where T : class
{
return target ?? EnsureInitialized (ref target, GetDefaultCtorValue<T>);
}
public static T EnsureInitialized<T> (ref T target, Func<T> valueFactory) where T : class
{
if (target == null) {
var value = valueFactory ();
if (value == null)
throw new InvalidOperationException ();
Interlocked.CompareExchange (ref target, value, null);
}
return target;
}
public static T EnsureInitialized<T> (ref T target, ref bool initialized, ref object syncLock)
{
return EnsureInitialized (ref target, ref initialized, ref syncLock, GetDefaultCtorValue<T>);
}
public static T EnsureInitialized<T> (ref T target, ref bool initialized, ref object syncLock, Func<T> valueFactory)
{
if (initialized)
return target;
if (syncLock == null)
Interlocked.CompareExchange (ref syncLock, new object (), null);
lock (syncLock) {
if (initialized)
return target;
initialized = true;
Thread.MemoryBarrier ();
target = valueFactory ();
}
return target;
}
static T GetDefaultCtorValue<T> ()
{
try {
return Activator.CreateInstance<T> ();
} catch {
throw new MissingMemberException ("The type being lazily initialized does not have a "
+ "public, parameterless constructor.");
}
}
}
}
#endif
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