为什么 ReadOnlyDictionary 不是线程安全的? [英] Why isn’t ReadOnlyDictionary thread-safe?

问题描述

我正在寻找可从多个线程访问的只读字典.虽然 ConcurrentDictionary 公开了这样的功能，但我不想有开销和奇怪的 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 在提供这样一个类的同时，文档指出只有静态调用是安全的.

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

不知道为什么?

推荐答案

ReadOnlyDictionary 只是任何其他字典的包装器.因此，它仅与底层字典一样线程安全.

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器读取，则无法保证安全.

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 从所有角度实际上是不可变的，您可以创建原始词典的副本，创建一个 ReadOnlyDictionary包装它，然后不在任何地方保留对克隆的引用.随着only 读取操作的进行，它应该是线程安全的.当然，如果键或值类型是可变的，那就会带来第二层线程不安全"的担忧.

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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