When will ConcurrentDictionary TryRemove return false

Question

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?

Question in code:

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); 

Edit: 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.

Answer 1

The ConcurrentDictionary does not suffer from race conditions. That's why you use it.

Return Value

true if an object was removed successfully; otherwise, false.

Answer 2

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.

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 (I think that was your concern, right?).