为什么ReadOnlyDictionary线程不安全? [英] Why isn’t ReadOnlyDictionary thread-safe?

问题描述

我正在寻找一个可以从多个线程访问的只读字典.尽管ConcurrentDictionary公开了此类功能，但我不想拥有额外的开销和奇怪的API.

I’m looking for a readonly-dictionary to be accessed from multiple threads. While ConcurrentDictionary exposes such capabilities, I don’t want to have the overhead and the strange API.

.Net 4.5提供此类时，文档指出仅静态调用是安全的.

.Net 4.5 while providing such a class, the documentation states that only static calls are safe.

我想知道为什么吗?

推荐答案

ReadOnlyDictionary 只是任何其他字典的包装.因此，它仅与基础字典一样具有线程安全性.

ReadOnlyDictionary is just a wrapper around any other dictionary. As such, it's only as thread-safe as the underlying dictionary.

特别是，如果有一个线程在修改底层字典，而另一个线程从包装程序中读取，则不能保证安全.

In particular, if there's a thread modifying the underlying dictionary while another thread reads from the wrapper, there's no guarantee of safety.

如果您想要一个ReadOnlyDictionary可以从 all 角度有效地不变，则可以创建原始词典的副本，在其周围创建一个ReadOnlyDictionary包装器，然后不保留引用到任何地方的克隆.随着 only 读取操作的进行，它应该是线程安全的.当然，如果键或值的类型是可变的，那将引发第二种线程不安全"的问题.

If you want a ReadOnlyDictionary which is effectively immutable from all angles, you can create a clone of the original dictionary, create a ReadOnlyDictionary wrapper around that, and then not keep a reference to the clone anywhere. With only read operations going on, it should then be thread-safe. Of course, if the key or value types are mutable, that opens up a second degree of "thread-unsafety" to worry about.

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