Concurrent collection supporting removal of a specified item?
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Quite simple: Other than ConcurrentDictionary (which I'll use if I have to but it's not really the correct concept), is there any Concurrent collection (IProducerConsumer implementation) that supports removal of specific items based on simple equality of an item or a predicate defining a condition for removal?

Explanation: I have a multi-threaded, multi-stage algorithm, which pulls objects from the DB and sticks them in a "starting" queue. From there they are grabbed by the next stage, further worked on, and stuffed into other queues. This process continues through a few more stages. Meanwhile, the first stage is invoked again by its supervisor and pulls objects out of the DB, and those can include objects still in process (because they haven't finished being processed and so haven't been re-persisted with the flag set saying they're done).

The solution I am designing is a master "in work" collection; objects go in that queue when they are retrieved for processing by the first stage, and are removed after they have been re-saved to the DB as "processed" by whatever stage of the workflow completed the necessary processing. While the object is in that list, it will be ignored if it is re-retrieved by the first stage.

I had planned to use a ConcurrentBag, but the only removal method removes an arbitrary item from the bag, not a specified one (and ConcurrentBag is *slow* in .NET 4). ConcurrentQueue and ConcurrentStack also do not allow removal of an item other than the next one it'll give you, leaving ConcurrentDictionary, which would work but is more than I need.

