您好,我这里有一些代码,但我不明白为什么我会遇到断点(见评论)。
这是 Microsoft 的一个我不知道或我没有正确理解的错误吗?
代码在 Debug 中进行了测试,但我认为它不应该改变任何东西。
注意:您可以直接在控制台应用程序中测试代码。
仅供引用...根据 supercat 的回答,我用建议的解决方案修复了我的代码,它运行良好:-) !!!不好的是静态字典的使用以及随之而来的性能,但它确实有效。 ... 几分钟后,我意识到 SuperCat 给了我所有提示,让我做得更好,解决静态字典问题,我做到了。代码示例是:
- 用 bug 编写代码
- 代码已更正但带有静态 ConditionalWeakTable
- 使用包含 SuperCat 技巧的 ConditioalWeakTable 编写代码(非常感谢他!)
示例...
using System;
using System.Collections.Generic;
using System.Diagnostics;
namespace WeakrefBug
{
// **********************************************************************
class B : IDisposable
{
public static List<B> AllBs = new List<B>();
public B()
{
AllBs.Add(this);
}
private bool disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!disposed)
{
AllBs.Remove(this);
disposed = true;
}
}
~B() { Dispose(false); }
}
// **********************************************************************
class A
{
WeakReference _weakB = new WeakReference(new B());
~A()
{
B b = _weakB.Target as B;
if (b == null)
{
if (B.AllBs.Count == 1)
{
Debugger.Break(); // b Is still referenced but my weak reference can't find it, why ?
}
}
else { b.Dispose(); }
}
}
// **********************************************************************
class Program
{
static void Main(string[] args)
{
A a = new A();
a = null;
GC.Collect(GC.MaxGeneration);
GC.WaitForPendingFinalizers();
}
}
// **********************************************************************
}
版本更正:
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;
namespace WeakrefBug // Working fine with ConditionalWeakTable
{
// **********************************************************************
class B : IDisposable
{
public static List<B> AllBs = new List<B>();
public B()
{
AllBs.Add(this);
}
private bool disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!disposed)
{
AllBs.Remove(this);
disposed = true;
}
}
~B() { Dispose(false); }
}
// **********************************************************************
class A
{
private static readonly System.Runtime.CompilerServices.ConditionalWeakTable<A, B> WeakBs = new ConditionalWeakTable<A, B>();
public A()
{
WeakBs.Add(this, new B());
}
public B CreateNewB()
{
B b = new B();
WeakBs.Remove(this);
WeakBs.Add(this, b);
return b;
}
~A()
{
B b;
WeakBs.TryGetValue(this, out b);
if (b == null)
{
if (B.AllBs.Count == 1)
{
Debugger.Break(); // B Is still referenced but my weak reference can't find it, why ?
}
}
else { b.Dispose(); }
}
}
// **********************************************************************
class Program
{
static void Main(string[] args)
{
A a = new A();
WeakReference weakB = new WeakReference(a.CreateNewB()); // Usually don't need the internal value, but only to ensure proper functionnality
a = null;
GC.Collect(GC.MaxGeneration);
GC.WaitForPendingFinalizers();
Debug.Assert(!weakB.IsAlive);
}
}
// **********************************************************************
}
使用包含 SuperCat 技巧的 ConditioalWeakTable 编写代码(非常感谢他!)
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;
namespace WeakrefBug // Working fine with non static ConditionalWeakTable - auto cleanup
{
// **********************************************************************
class B : IDisposable
{
public static List<B> AllBs = new List<B>();
public B()
{
AllBs.Add(this);
}
private bool disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!disposed)
{
AllBs.Remove(this);
disposed = true;
}
}
~B() { Dispose(false); }
}
// **********************************************************************
class A
{
private ConditionalWeakTable<object, object> _weakBs = null;
public A()
{
}
public B CreateNewB()
{
B b = new B();
if (_weakBs == null)
{
_weakBs = new ConditionalWeakTable<object, object>();
_weakBs.Add(b, _weakBs);
}
_weakBs.Remove(this);
_weakBs.Add(this, b);
return b;
}
internal ConditionalWeakTable<object, object> ConditionalWeakTable // TestOnly
{
get { return _weakBs; }
}
~A()
{
object objB;
_weakBs.TryGetValue(this, out objB);
if (objB == null)
{
if (B.AllBs.Count == 1)
{
Debugger.Break(); // B Is still referenced but my weak reference can't find it, why ?
}
}
else
{
((B)objB).Dispose();
}
}
}
// **********************************************************************
class Program
{
static void Main(string[] args)
{
A a = new A();
WeakReference weakB = new WeakReference(a.CreateNewB()); // Usually don't need the internal value, but only to ensure proper functionnality
WeakReference weakConditionalWeakTable = new WeakReference(a.ConditionalWeakTable);
a = null;
GC.Collect(GC.MaxGeneration);
GC.WaitForPendingFinalizers();
Debug.Assert(!weakB.IsAlive);
Debug.Assert(!weakConditionalWeakTable.IsAlive);
}
}
// **********************************************************************
}
CitizenInsane 的以下问题... 我不记得我为什么这么做了……我找到了我的样本,但当时并不确定我的意图。我试图弄清楚并提供了以下代码,我觉得更清楚但仍然不记得我最初的需要。抱歉???
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;
namespace WeakrefBug // Working fine with ConditionalWeakTable
{
// **********************************************************************
class B : IDisposable
{
public static List<B> AllBs = new List<B>();
public B()
{
AllBs.Add(this);
}
private bool disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!disposed)
{
AllBs.Remove(this);
disposed = true;
}
}
~B() { Dispose(false); }
}
// **********************************************************************
class A
{
private ConditionalWeakTable<object, object> _weakBs = null;
private WeakReference _weakB = null;
public A()
{
_weakBs = new ConditionalWeakTable<object, object>();
B b = new B();
_weakB = new WeakReference(b);
_weakBs.Add(b, _weakB);
}
public B B
{
get
{
return _weakB.Target as B;
}
set { _weakB.Target = value; }
}
internal ConditionalWeakTable<object, object> ConditionalWeakTable // TestOnly
{
get { return _weakBs; }
}
~A()
{
B objB = B;
if (objB == null)
{
if (B.AllBs.Count == 1)
{
Debugger.Break(); // B Is still referenced but my weak reference can't find it, why ?
}
}
else
{
((B)objB).Dispose();
}
}
}
// **********************************************************************
class Program
{
static void Main(string[] args)
{
Test1();
Test2();
}
private static void Test1()
{
A a = new A();
WeakReference weakB = new WeakReference(a.B); // Usually don't need the internal value, but only to ensure proper functionnality
WeakReference weakConditionalWeakTable = new WeakReference(a.ConditionalWeakTable);
a = null;
GC.Collect(GC.MaxGeneration);
GC.WaitForPendingFinalizers();
Debug.Assert(B.AllBs.Count == 0);
GC.Collect(GC.MaxGeneration);
GC.WaitForPendingFinalizers();
Debug.Assert(!weakB.IsAlive); // Need second pass of Collection to be collected
Debug.Assert(!weakConditionalWeakTable.IsAlive);
}
private static void Test2()
{
A a = new A();
WeakReference weakB = new WeakReference(a.B);
B.AllBs.Clear();
a.B = null;
GC.Collect(GC.MaxGeneration);
GC.WaitForPendingFinalizers();
Debug.Assert(!weakB.IsAlive); // Need second pass of Collection to be collected
}
}
// **********************************************************************
}
最佳答案
WeakReference
的一个有时令人讨厌的限制那是WeakReference
吗如果不存在对 WeakReference
的强根引用,则可能无效本身,即使 trackResurrection
也可能发生这种情况构造函数参数为 true
,即使 WeakReference
的目标根深蒂固。此行为源于一个事实 WeakReference
有一个非托管资源(一个 GC 句柄)并且如果 WeakReference
的终结器没有清理GC句柄,永远清理不掉,会构成内存泄漏。
如果对象的终结器有必要使用 WeakReference
对象,该对象必须做出一些规定以确保这些对象保持强引用。我不确定完成此操作的最佳模式是什么,但是 ConditionalWeakTable<TKey,TValue>
在 .net 4.0 中添加的那个可能会有用。有点像Dictionary<TKey,TValue>
除了只要表本身是强引用的,并且给定的键是强引用的,那么它对应的值就会被认为是强引用的。请注意,如果 ConditionalWeakTable
拥有一个链接 X 到 Y 和 Y 到表的条目,那么只要 X 或 Y 仍然存在,该表也将保持不变。
关于C# WeakReference 对象在终结器中为 NULL,但仍被强引用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15093762/