Ayende @ Rahien

Gian Maria Ricci commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Wed, 06 Apr 2011 07:24:01 GMT

It would be nice if the documentation of GetOrAdd contains a remark telling you that the factory function could be called more than one times. I agree that we should never assume something :), but this violates the Principle of least astonishment. Thanks Ayende for pointed this out.

Ara commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 17:57:24 GMT

I meant, ConcurrentDictionary[TKey, Lazy[TValue] ]

Ara commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 17:56:11 GMT

Use ConcurrentDictionary > When this happens, two instances of Lazy

Nick Sergeev commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 17:06:37 GMT

WTF?! I think MS should remove this method from ConcurrentDictionary.

Frank Quednau commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 17:03:43 GMT

Oh, Benny Hill, awesome :) That is a nasty one to remember. Peter, ayende was referring to the implementation of ConcurrentDictionary

Peter Morris commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 15:11:47 GMT

I don't know what you mean by "There are no locks" - WaitOne() is a lock isn't it, or do you mean something else?

tobi commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 12:57:38 GMT

The reason for this is that user code should not be called while holding a lock (deadlock-prone. who knows if you function will call across threads and deadlock with itself?). Therefore the CDict will release the lock before calling your delegate. (They are internally using normal locks, but striped by hash code).

Konstantin commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 12:28:06 GMT

There is a concept of "publish once" and "execute once" in Lazy If you only need "publish once" guarantee, framework can make more performance optimizations. Unfortunately this does not seem to have been documented for ConfurrentDictionary

Ayende Rahien commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 10:58:50 GMT

Linkgoron, To make sure that this actually run on separate threads.

Linkgoron commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 10:56:33 GMT

Ayende, they're not totally lock free... But the delegate executes before the lock. BTW, is there any reason you're using Threads instead of Tasks/TPL, or is just for demonstration?

Michael Hawksworth commented on ConcurrentDIctionary.GetOrAdd may call the valueFactory method more than once

Tue, 05 Apr 2011 09:35:08 GMT

I always try to remember... [http://www.youtube.com/watch?v=6hrLj8QEAgI](http://www.youtube.com/watch?v=6hrLj8QEAgI)