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A .Net4 Gem: The ConcurrentDictionary - Tips & Tricks

Answer 1

A:

ConcurrentDictionary is thread-safe. You do not have to worry about it even when using it from multiple threads.

Tom Cabanski 2010-04-20 19:52:09

Answer 2

+2 A:

I have had no issues with the Concurrent collection objects so far. They are a huge boost to my productivity by allowing me to not worry about concurrency issues with the collections and focus on writing application logic.

This is not to say there are no issues. Just nothing I've run into.

ChaosPandion 2010-04-20 19:57:25

Thank you Chaos +1

SDReyes 2010-04-20 19:59:33

Answer 3

+14 A:

Members are thread-safe, but you shouldn't expect a sequence of calls to be thread-safe. For example you can't expect the following to be thread-safe:

if (!dictionary.ContainsKey(key))
{
    // Another thread may have beaten you to it
    dictionary.Add(key, value);
}

Instead, use the new thread-safe API - e.g. AddOrUpdate (last one wins in the event of a race condition) or GetOrAdd (first one wins in the event of a race condition).

Joe 2010-04-20 20:31:17

Very useful Joe Thanks! +1

SDReyes 2010-04-20 20:55:20

This is a far better answer than the accepted answer.

Martin 2010-04-20 21:11:07

I'm going to wait for more responses now, Martin. Thanks : )

SDReyes 2010-04-20 23:45:00

@Martin - I agree. :)

ChaosPandion 2010-04-21 02:09:47

Note that the MS documentation says here: http://msdn.microsoft.com/en-us/library/dd997369.aspx that GetOrAdd and AddOrUpdate may not return the same item that you inserted. I believe this is just for the Function<> variant of the methods but the writing is ambiguous.

evilfred 2010-06-23 19:26:48

@evilfred, this does apply to the Func<> variant - the description makes this clear. The Func<> variant essentially allows you to create a lazy-loaded dictionary, and in practice I'd expect all threads to be using the same delegate, and that the result returned by multiple invocations of the delegate are interchangeable (e.g. immutable).

Joe 2010-06-24 06:08:33

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A .Net4 Gem: The ConcurrentDictionary - Tips & Tricks

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