这是否使用字典线程安全?

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问题描述

限时送ChatGPT账号..

这是我的两个方法变体，它返回一个与枚举值相关联的字符串(保存在字典中).第一个变体较慢，但线程安全，第二个变体更快，但我不知道它是否是线程安全的.第一:

Here is two my variants of method, which returns a string, associated with enum value (kept in dictionary). First variant is slower, but thread-safe, second is faster, but i don't know, whether it is thread-safe or not. First:

string GetStringForEnum (SomeEnum e)
{
   string str = null;
   lock (someDictionary) //someDictionary is not used anywhere else (only in this method)
   { if (!someDictionary (e, out str)) { someDictionary.Add (e, "somehowCreatedString"); }
   return str;
}

第二个变体:

string GetStringForEnum (SomeEnum e)
{
   string str = null;
   if (!someDictionary (e, out str))
   {
     lock (someDictionary) //someDictionary is not used anywhere else (only in this method)
     { if (!someDictionary (e, out str)) { someDictionary.Add (e, "somehowCreatedString"); }
   }
   return str;
}

第二个变种不是每次都使用锁"，但它是否是线程安全的?

Second variant is not used "lock" each time, but is it thread-safe or not?

推荐答案

这里有两个问题:

lock (someDictionary) - 不建议这样做，即使字典没有在其他地方使用.这是一个理论上的论点，但 Dictionary 类的(未来)代码可以锁定自身.

lock (someDictionary) - this is dis-advised, even if the dictionary is not used elsewhere. It is a theoretical argument but the (future) code of the Dictionary class could lock on itself.

if (!someDictionary (e, out str)) 没有锁.我假设这是对 TryGetValue() 的调用.这根本不是线程安全的，您的 Read 可能会被另一个线程中的 Write 中断.这可能以各种错误结束(索引超出范围，空引用).错误将非常罕见(= 难以重现).

if (!someDictionary (e, out str)) without a lock. I assume this is a call to TryGetValue(). This simply is not thread-safe, your Read could be interrupted by a Write in another thread. This could end in all sorts of errors (index out of range, null reference). The errors will be very rare (= hard to reproduce).

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