source: branches/2994-AutoDiffForIntervals/HeuristicLab.ExtLibs/HeuristicLab.NRefactory/5.5.0/NRefactory-5.5.0/Utils/BusyManager.cs

// Copyright (c) 2010-2013 AlphaSierraPapa for the SharpDevelop Team
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// 
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// 
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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);
    }
  }
}