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