可以使用字符串作为锁定对象吗? [英] Is it OK to use a string as a lock object?

问题描述

我需要根据有限的字符串集在一个区域中创建一个临界区.我希望为同一个字符串实例共享锁，(有点类似于 String.Intern 方法).

I need to make a critical section in an area on the basis of a finite set of strings. I want the lock to be shared for the same string instance, (somewhat similar to String.Intern approach).

我正在考虑以下实现:

public class Foo
{
    private readonly string _s;
    private static readonly HashSet<string> _locks = new HashSet<string>();

    public Foo(string s)
    {
        _s = s;
        _locks.Add(s);
    }

    public void LockMethod()
    {
        lock(_locks.Single(l => l == _s))
        {
            ...
        }
    }
}

这种方法有什么问题吗?以这种方式锁定字符串对象是否可以，使用HashSet是否存在线程安全问题?

Are there any problems with this approach? Is it OK to lock on a string object in this way, and are there any thread safety issues in using the HashSet<string>?

例如，创建一个 Dictionary 为每个字符串实例创建一个新的锁对象是否更好?

Is it better to, for example, create a Dictionary<string, object> that creates a new lock object for each string instance?

最终实施

根据建议，我进行了以下实施:

Based on the suggestions I went with the following implementation:

public class Foo
{
    private readonly string _s;
    private static readonly ConcurrentDictionary<string, object> _locks = new ConcurrentDictionary<string, object>();

    public Foo(string s)
    {
        _s = s;
    }

    public void LockMethod()
    {
        lock(_locks.GetOrAdd(_s, _ => new object()))
        {
            ...
        }
    }
}

推荐答案

不鼓励锁定字符串，主要原因是(因为字符串实习)某些其他代码可能会在您不知道的情况下锁定同一个字符串实例.创造潜在的死锁情况.

Locking on strings is discouraged, the main reason is that (because of string-interning) some other code could lock on the same string instance without you knowing this. Creating a potential for deadlock situations.

现在，在大多数具体情况下，这可能是一个牵强的场景.这更像是图书馆的一般规则.

Now this is probably a far fetched scenario in most concrete situations. It's more a general rule for libraries.

但另一方面，字符串的感知好处是什么?

But on the other hand, what is the perceived benefit of strings?

所以，一点一点:

这种方法有什么问题吗?

Are there any problems with this approach?

是的，但主要是理论性的.

Yes, but mostly theoretical.

以这种方式锁定字符串对象是否可以，使用HashSet是否存在线程安全问题?

Is it OK to lock on a string object in this way, and are there any thread safety issues in using the HashSet?

HashSet<> 不涉及线程安全，只要线程只并发读取即可.

The HashSet<> is not involved in the thread-safety as long as the threads only read concurrently.

例如，创建一个为每个字符串实例创建一个新锁对象的 Dictionary 是否更好?

Is it better to, for example, create a Dictionary that creates a new lock object for each string instance?

是的.只是为了安全起见.在大型系统中，避免死锁的主要目的是使锁对象尽可能保持本地和私有.只有有限数量的代码才能访问它们.

Yes. Just to be on the safe side. In a large system the main aim for avoiding deadlock is to keep the lock-objects as local and private as possible. Only a limited amount of code should be able to access them.

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