Socket synchronous/Asynchronous vs. blocking/non-blocking differences

On the Internet to read a lot of answers, also did not find the appropriate, perhaps this article is not the appropriate answer:)

Synchronous and asynchronous are concerned with the message communication mechanism, while blocking non-blocking is concerned with the state of the program while waiting for the result (message, return value) of the call.

Synchronous/asynchronous is the way the API is notified by callers. Blocking/non-blocking is the way the API caller waits.

synchronous, asynchronous, and blocking, non-blocking are composite relationships.

So there are 4 ways:

1. Synchronous blocking

2. Synchronous non-blocking

3. Asynchronous blocking

4. Asynchronous non-blocking

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Recv and Recvfrom:

Recv only the function returns after receiving the message, this is blocking.

The Recvfrom returns immediately, which is non-blocking.

For recvfrom, how do I receive a message because the function returns immediately? There are 2 ways of doing this:

1. Open a thread, keep the Select, this is synchronous

2. With an asynchronous mechanism, a message is notified when the system receives a message, which is asynchronous .

It seems that the above description only three kinds, blocking, synchronous non-blocking, asynchronous non-blocking, why?

because generally, since the use of blocking, with synchronization is good, (generally) with async a bit redundant , because the caller knows already received, but also need system notification?

I think that's why it's easy to confuse these 2 sets of concepts (there are few asynchronous blocking patterns, and some scenarios may need to be used).

Socket synchronous/Asynchronous vs. blocking/non-blocking differences