FinalizerDemo.cs

// Compile using:
// csc /target:winexe /noconfig /define:DEBUG FinalizerDemo.cs /r:System.dll /r:System.Windows.Forms.dll

// Self-contained demonstration code for:
// http://stackoverflow.com/questions/792660/is-gc-suppressfinalize-guaranteed

using WikiPad;
using System;
using System.Windows.Forms;

public class Program
{
    public static void Main(string[] args)
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);

        var form = new Form();
        var button = new Button
        {
            Text = "Work, baby, work!",
            Dock = DockStyle.Fill
        };
        button.Click += delegate
        {
            if (args.Length > 0 && args[0].Equals("notusing", StringComparison.OrdinalIgnoreCase))
            {
                CurrentCursorScope.EnterWait();      // the wrong way that will
                System.Threading.Thread.Sleep(1000); // trigger warning on exit
            }
            else
            {
                using (CurrentCursorScope.EnterWait())   // the right way
                    System.Threading.Thread.Sleep(1000);
            }
        };
        form.Controls.Add(button);
        
        Application.Run(form);
        GC.WaitForPendingFinalizers();
    }
}

#region License, Terms and Author(s)
//
// Schnell - Wiki widgets
// Copyright (c) 2007 Atif Aziz. All rights reserved.
//
//  Author(s):
//      Atif Aziz, http://www.raboof.com
//
// This library is free software; you can redistribute it and/or modify it 
// under the terms of the GNU Lesser General Public License as published by 
// the Free Software Foundation; either version 2.1 of the License, or (at 
// your option) any later version.
//
// This library is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
// License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this library; if not, write to the Free Software Foundation, 
// Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 
//
#endregion

namespace WikiPad
{
    #region Imports

    using System;
    using System.Diagnostics;

    #endregion

    //
    // NOTE: To use SingletonScope and ISingletonScopeHelper with value 
    // types, use Nullable<T>. For example, if the type of value to scope
    // is ThreadPriority then use ISingletonScopeHelper<ThreadPriority?>
    // and SingletonScope<ThreadPriority?>.
    //

    //
    // In debug builds, this type is defined as a class so a finalizer
    // can be used to detect an undisposed scope.
    //
    
    /// <summary>
    /// Designed to change a singleton and scope that change. After exiting
    /// the scope, the singleton is restored to its value prior to entering
    /// the scope.
    /// </summary>

    #if !DEBUG
    internal struct SingletonScope<T, H> 
    #else
    internal sealed class SingletonScope<T, H> 
    #endif
        : IDisposable 
        where H : ISingletonScopeHelper<T>, new()
    {
        private T _old;
        
        public SingletonScope(T temp)
        {
            _old = Helper.Install(temp);
        }

        private static H Helper
        {
            get { return new H(); }
        }

        public void Dispose()
        {
            //
            // First, transfer fields to stack then nuke the fields.
            //
            
            T old = _old;
            
            //
            // Already disposed?
            //

            if (old == null)
                return;
            
            _old = default(T);
            
            //
            // Shazam! Restore the old value.
            //
            
            Helper.Restore(old);

            #if DEBUG
            GC.SuppressFinalize(this); // Only when defined as a class!
            #endif
        }

        #if DEBUG
        
        //
        // This finalizer is used to detect an undisposed scope. This will
        // only indicate that the scope was not disposed but (unfortunately)
        // not which one and where since GC will probably collect much later
        // than it should have been disposed.
        //
        
        ~SingletonScope()
        {
            Debug.Fail("Scope for " + typeof(T).FullName + " not disposed!");
        }
        
        #endif
    }
}

#region License, Terms and Author(s)
//
// Schnell - Wiki widgets
// Copyright (c) 2007 Atif Aziz. All rights reserved.
//
//  Author(s):
//      Atif Aziz, http://www.raboof.com
//
// This library is free software; you can redistribute it and/or modify it 
// under the terms of the GNU Lesser General Public License as published by 
// the Free Software Foundation; either version 2.1 of the License, or (at 
// your option) any later version.
//
// This library is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
// License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this library; if not, write to the Free Software Foundation, 
// Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 
//
#endregion

namespace WikiPad
{
    /// <summary>
    /// Provides helper implementation to SingletonScope for installing
    /// and restoring the singleton value.
    /// </summary>

    internal interface ISingletonScopeHelper<T>
    {
        T Install(T temp);
        void Restore(T old);
    }
}

#region License, Terms and Author(s)
//
// Schnell - Wiki widgets
// Copyright (c) 2007 Atif Aziz. All rights reserved.
//
//  Author(s):
//      Atif Aziz, http://www.raboof.com
//
// This library is free software; you can redistribute it and/or modify it 
// under the terms of the GNU Lesser General Public License as published by 
// the Free Software Foundation; either version 2.1 of the License, or (at 
// your option) any later version.
//
// This library is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
// License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with this library; if not, write to the Free Software Foundation, 
// Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 
//
#endregion

namespace WikiPad
{
    #region Imports

    using System.Windows.Forms;

    #endregion
    
    internal static class CurrentCursorScope
    {
        public static SingletonScope<Cursor, Helper> EnterWait()
        {
            return Enter(Cursors.WaitCursor);
        }

        public static SingletonScope<Cursor, Helper> Enter(Cursor cursor)
        {
            return new SingletonScope<Cursor, Helper>(cursor);
        }

        internal struct Helper : ISingletonScopeHelper<Cursor>
        {
            public Cursor Install(Cursor temp)
            {
                var save = Cursor.Current;
                Cursor.Current = temp;
                return save;
            }

            public void Restore(Cursor old)
            {
                Cursor.Current = old;
            }
        }
    }
}