ConcurrentDictionary TryRemove何时返回false [英] When will ConcurrentDictionary TryRemove return false

问题描述

如果字典不包含给定键的值，它只会返回false还是由于线程争用条件而返回false，就像另一个线程添加/更新某些东西一样？

Will it only return false if the dictionary does not contain a value for the given key or will it also return false due to thread race conditions, like another thread adds/updates something?

代码中的问题：

ConcurrentDictionary<int, string> cd = new ConcurrentDictionary<int, string>();

// This might fail if another thread is adding with key value of 1.
cd.TryAdd(1, "one"); 

// Will this ever fail if no other thread ever removes with the key value of 1?
cd.TryRemove(1); 

编辑：
我认为它只会返回false如果它不包含给定键的值，但要绝对确定。

I think that it only will return false if it does not contain a value for the given key, but want to be absolutely sure.

推荐答案

同时Mitch是正确的表示 ConcurrentDictionary 不容易受到比赛条件的影响，我认为您所提出的问题的答案是，是的，如果存在密钥， TryRemove 将起作用并返回 true 。

While Mitch is right that a ConcurrentDictionary is not vulnerable to race conditions, I think the answer to the question you are asking is that yes, if the key is present, TryRemove will work and will return true.

在您发布的代码中， TryRemove 将返回 false ，因为 cd 是一个在其他任何地方都无法访问的局部变量。但是，如果其他地方的某些代码引用了此 ConcurrentDictionary 对象，并且正在删除单独线程上的键，则 TryRemove 仍可能返回 false ，但仅是因为密钥已被删除，而不是因为正在对密钥执行其他操作字典，并且密钥被卡在那里。

In the code you posted, there's no way that TryRemove would return false since cd is a local variable not accessed anywhere else. But if some code elsewhere were given a reference to this ConcurrentDictionary object and were removing keys on a separate thread, then it's possible that TryRemove could return false, even here -- but only because the key was already removed, not because some other action is being performed on the dictionary and the key is somehow "stuck" there.

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