BlockingCollection Max Size

Question

I understand that BlockingCollection using ConcurrentQueue has a boundedcapacity of 100.

However I'm unsure as to what that means.

I'm trying to achieve a concurrent cache which, can dequeue, can deque/enque in one operation if the queue size is too large, (i.e. loose messages when the cache overflows). Is there a way to use boundedcapacity for this or is it better to manually do this or create a new collection.

Basically I have a reading thread and several writing threads. I would like it if the data in the queue is the "freshest" of all the writers.

Answer 1

A bounded capacity of N means that if the queue already contains N items, any thread attempting to add another item will block until a different thread removes an item.

What you seem to want is a different concept - you want most recently added item to be the first item that is dequeued by the consuming thread.

You can achieve that by using a ConcurrentStack rather than a ConcurrentQueue for the underlying store.

You would use this constructor and pass in a ConcurrentStack.

For example:

var blockingCollection = new BlockingCollection<int>(new ConcurrentStack<int>());

By using ConcurrentStack, you ensure that each item that the consuming thread dequeues will be the freshest item in the queue at that time.

Also note that if you specify an upper bound for the blocking collection, you can use BlockingCollection.TryAdd() which will return false if the collection was full at the time you called it.