How to remove a single, specific object from a ConcurrentBag<>?

With the new ConcurrentBag<T> in .NET 4, how do you remove a certain, specific object from it when only TryTake() and TryPeek() are available?

I'm thinking of using TryTake() and then just adding the resulting object back into the list if I don't want to remove it, but I feel like I might be missing something. Is this the correct way?

Solution 1:

The short answer: you can't do it in an easy way.

The ConcurrentBag keeps a thread local queue for each thread and it only looks at other threads' queues once its own queue becomes empty. If you remove an item and put it back then the next item you remove may be the same item again. There is no guarantee that repeatedly removing items and putting them back will allow you to iterate over the all the items.

Two alternatives for you:

• Remove all items and remember them, until you find the one you want to remove, then put the others back afterwards. Note that if two threads try to do this simultaneously you will have problems.
• Use a more suitable data structure such as ConcurrentDictionary.

Solution 2:

You can't. Its a bag, it isn't ordered. When you put it back, you'll just get stuck in an endless loop.

You want a Set. You can emulate one with ConcurrentDictionary. Or a HashSet that you protect yourself with a lock.