是否有可能建立在C＃中忠实地弱密钥的字典吗？ [英] Is it possible to create a truely weak-keyed dictionary in C#?

问题描述

我想螺母的细节一个真正的 WeakKeyedDictionary＆LT;，＆GT; 的C＃...但我遇到困难

我意识到这是一个不平凡的任务，但似乎没有能力来声明 WeakKeyedKeyValuePair＆LT;，＆GT; （其中GC只有遵循的价值基准，如果关键可达），使得它看起来不可能。

有两个主要的问题，我看到的：

1. 到目前为止，我所看到的每一个执行不剪裁值键已收集后。想想 - 对使用这样的字典的主要原因之一是prevent被保留这些值各地（不仅仅是钥匙！），因为它们是无法访问的，但在这里，他们留下指向强引用<。 / P>

   是的，添加/从字典中删除足够的，他们最终会被取代，但如果你不这样做？

2. 如果没有一个假设 WeakKeyedKeyValuePair＆LT;，＆GT; （或告诉GC只标出值，如果关键是可达的另一种方式）的任何值，是指它的键永远不会被收集。这是存储任意值，当出现问题。

1的问题可以解决在一个相当不理想/ hackish的方法：用GC通知等待一个完整的GC完成，然后一起去剪枝字典在另一个线程。这一次我是半确定与

但问题2有我难住了。我意识到这是很容易被所以不要做反驳，但它有我疑惑 - 这方面的问题，甚至可能解决

解决方案

有一个看 ConditionalWeakTable＆LT; TKEY的，TValue＆GT;类。

  

使编译器动态附加对象字段被管理对象。

它本质上是一本字典，其中两个键和值是 WeakReference的，且该值被保持活只要键是活的。

请注意！此类不使用 GetHash code 和等于做相等比较，它使用了的ReferenceEquals 。

I'm trying to nut out the details for a true WeakKeyedDictionary<,> for C#... but I'm running into difficulties.

I realise this is a non-trivial task, but the seeming inability to declare a WeakKeyedKeyValuePair<,> (where the GC only follows the value reference if the key is reachable) makes it seemingly impossible.

There are two main problems I see:

1. Every implementation I've so far seen does not trim values after keys have been collected. Think about that - one of the main reasons for using such a Dictionary is to prevent those values being kept around (not just the keys!) as they're unreachable, but here they are left pointed to by strong references.

   Yes, add/remove from the Dictionary enough and they'll eventually be replaced, but what if you don't?

2. Without a hypothetical WeakKeyedKeyValuePair<,> (or another means of telling the GC to only mark the value if the key is reachable) any value that refers to it's key would never be collected. This is a problem when storing arbitrary values.

Problem 1 could be tackled in a fairly non-ideal/hackish way : use GC Notifications to wait for a full GC to complete, and then go along and prune the dictionary in another thread. This one I'm semi-ok with.

But problem 2 has me stumped. I realise this is easily countered by a "so don't do that", but it has me wondering - is this problem even possible to solve?

解决方案

Have a look at the ConditionalWeakTable<TKey, TValue> Class.

Enables compilers to dynamically attach object fields to managed objects.

It's essentially a dictionary where both the key and the value are a WeakReference, and the value is kept alive as long as the key is alive.

Note! This class does not use GetHashCode and Equals to do equality comparisons, it uses ReferenceEquals.

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