// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
// 
// 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
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// 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
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// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;

namespace ICSharpCode.NRefactory.Utils
{
	/// <summary>
	/// This class is used to prevent stack overflows by representing a 'busy' flag
	/// that prevents reentrance when another call is running.
	/// However, using a simple 'bool busy' is not thread-safe, so we use a
	/// thread-static BusyManager.
	/// </summary>
	public static class BusyManager
	{
		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1815:OverrideEqualsAndOperatorEqualsOnValueTypes")]
		[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Design", "CA1034:NestedTypesShouldNotBeVisible",
		                                                 Justification = "Should always be used with 'var'")]
		public struct BusyLock : IDisposable
		{
			public static readonly BusyLock Failed = new BusyLock(null);
			
			readonly List<object> objectList;
			
			internal BusyLock(List<object> objectList)
			{
				this.objectList = objectList;
			}
			
			public bool Success {
				get { return objectList != null; }
			}
			
			public void Dispose()
			{
				if (objectList != null) {
					objectList.RemoveAt(objectList.Count - 1);
				}
			}
		}
		
		[ThreadStatic] static List<object> _activeObjects;
		
		public static BusyLock Enter(object obj)
		{
			List<object> activeObjects = _activeObjects;
			if (activeObjects == null)
				activeObjects = _activeObjects = new List<object>();
			for (int i = 0; i < activeObjects.Count; i++) {
				if (activeObjects[i] == obj)
					return BusyLock.Failed;
			}
			activeObjects.Add(obj);
			return new BusyLock(activeObjects);
		}
	}
}