source: branches/PersistentDataStructures/HeuristicLab.ExtLibs/HeuristicLab.AvalonEdit/5.0.1/AvalonEdit-5.0.1/Utils/CallbackOnDispose.cs

// Copyright (c) 2014 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
// 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
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// DEALINGS IN THE SOFTWARE.

using System;
using System.Collections.Generic;
using System.Threading;

namespace ICSharpCode.AvalonEdit.Utils
{
  /// <summary>
  /// Invokes an action when it is disposed.
  /// </summary>
  /// <remarks>
  /// This class ensures the callback is invoked at most once,
  /// even when Dispose is called on multiple threads.
  /// </remarks>
  sealed class CallbackOnDispose : IDisposable
  {
    Action action;
    
    public CallbackOnDispose(Action action)
    {
      if (action == null)
        throw new ArgumentNullException("action");
      this.action = action;
    }
    
    public void Dispose()
    {
      Action a = Interlocked.Exchange(ref action, null);
      if (a != null) {
        a();
      }
    }
  }
  
  /// <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>
  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);
    }
  }
}