To add items to a block you can either use
Post will try to add the item synchronously and return a
bool saying whether it succeeded or not. It may not succeed when, for example, a block has reached its
BoundedCapcity and has no more room for new items yet.
SendAsync on the other hand will return an uncompleted
Task<bool> that you can
await. That task will complete in the future with a
true result when the block cleared its internal queue and can accept more items or with a
false result if it's declining permanently (e.g. as a result of cancellation).