c# - GC.SuppressFinalize 有保证吗？

Question

我在实践中的观察是GC.SuppressFinalize并不总是抑制对终结器的调用。尽管如此，终结器可能还是被调用了。因此，我想知道 GC.SuppressFinalize 是否具有请求的性质，而不是系统的保证？

---

更多信息

如果需要，以下信息可能有助于为问题提供更多背景信息。

GC.SuppressFinalize文档摘要确实声明这是一个请求:

Requests that the system not call the finalizer for the specified object.

我想知道这是随意使用该词还是真正旨在描述运行时行为。

我已经通过从 Schnell 中获取的以下 SingletonScope 类观察到这一点项目，基于 original idea by Ian Griffiths除了它更普遍。这个想法是在调试版本中检测 Dispose 方法是否被调用。如果没有，终结器最终会启动，并且可以发出警告。如果调用 Dispose，则 GC.SuppressFinalize 应该 阻止终结器触发。不幸的是，警告似乎无论如何都会触发，但不是确定性的。也就是说，它们不会在每次运行时都开火。

#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.
            //

            var old = _old;
            _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
    }
}

---

完整的工作示例可在 http://gist.github.com/102424 获得。带有编译说明，但请注意，到目前为止，无法确定地重现该问题。

Answer 1

您可能看到的一个奇怪现象是，即使实例方法仍在运行，终结器仍然可以运行，只要该实例方法稍后不使用任何变量。因此，在您的示例代码中，Dispose 方法在第一行之后不使用任何实例变量。然后可以完成实例，即使 Dispose 仍在运行。

如果您在 Dispose 方法的末尾插入对 GC.KeepAlive(this) 的调用，您可能会发现问题所在离开。

Chris Brumme 有一个 blog post关于这个，我认为附近还有另一个……