Multiple consumers and querying a C# BlockingCollection

Multiple consumers can just call Take or TryTake concurrently - each item will only be consumed by a single consumer.

However, I believe GetConsumingEnumerable will also do what you want. I believe if each caller calls that, each will get a separate consuming enumerable, which again will make sure that each item is only consumed once. I'm not sure offhand what happens when the queue becomes empty - I don't know whether MoveNext() then blocks, or returns false.

I didn't really follow your second question though...