TPL Dataflow, whats the functional difference between Post() and SendAsync()?

Question

I am confused about the difference between sending items through Post() or SendAsync(). My understanding is that in all cases once an item reached the input buffer of a data

Answer 1

The documentation makes this reasonably clear, IMO. In particular, for Post:

This method will return once the target block has decided to accept or decline the item, but unless otherwise dictated by special semantics of the target block, it does not wait for the item to actually be processed.

And:

For target blocks that support postponing offered messages, or for blocks that may do more processing in their Post implementation, consider using SendAsync, which will return immediately and will enable the target to postpone the posted message and later consume it after SendAsync returns.

In other words, while both are asynchronous with respect to processing the message, SendAsync allows the target block to decide whether or not to accept the message asynchronously too.

It sounds like SendAsync is a generally "more asynchronous" approach, and one which is probably encouraged in general. What isn't clear to me is why both are required, as it certainly sounds like Post is broadly equivalent to using SendAsync and then just waiting on the result. As noted in comments, there is one significant difference: if the buffer is full, Post will immediately reject, whereas SendAsync doesn't.