non-blocking IO vs async IO and implementation in Java

Question

Trying to summarize for myself the difference between these 2 concepts (because I\'m really confused when I see people are using both of them in one sentence, like \"non-blo

Answer 1

I would say there are three types of io:

synchronous blocking
synchronous non-blocking
asynchronous

Both synchronous non-blocking and asynchronous would be considered non-blocking as the calling thread is not waiting on the IO to complete. So while non-blocking asynchronous io might be redundant, they are not one in the same. When I open a file I can open it in non-blocking mode. What does this mean? It means when I issue a read() it won't block. It will either return me the bytes that are available or indicate that there are no bytes available. If I didn't enable non-blocking io the read() would block until data was available. I might want to enable non-blocking io if I want a thread to handle multiple io requests. For instance, I could use select() to find out what file descriptors, or maybe sockets, have data available to read. I then do synchronous reads on those file descriptors. None of those reads should block because I already know data is available, plus I have opened the file descriptors in non-blocking mode.

Asynchronous io is where you issue an io request. That request is queued, and thus doesn't block the issuing thread. You are notified when either the request failed or has completed successfully.