Multiple consumers and querying a C# BlockingCollection

Question

I am using a .NET 4.0 BlockingCollection to handle a queue of items that each need to be processed by an operation that can take up to a second to process each item. This queue

Answer 1

GetConsumingEnumerable is in fact safe to call from multiple consumers simultaneously; the enumerable only completes when the collection is marked as complete. Each item is only consumed once.

GetConsumingEnumerable is essentially equivalent to:

while (!IsCompleted)
{
  if (TryTake(out var item, Timeout.Infinite))
    yield return item;
}

plus a bit of cancellation/cleanup logic.

Answer 2

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...