aio_read和read / EWOULDBLOCK有什么区别？

Question

In aio_read, we use aio_error function on a aiocb struct to check whether operation is finished. To me, it seems as polling and same as read followed by checking EWOULDBLOCK as a return value.

Answer 1

we use aio_error function on a aiocb struct to check whether operation is finished.

No we don't. We use it to check whether it finished with an error.

To me, it seems as polling and same as read followed by checking EWOULDBLOCK as a return value.

No. If the operation hasn't finished, with or without an error, it continues, asynchronously. EWOULDBLOCK means the operation has finished and without transferring any data.

You should certainly not 'poll' when using async I/O: you should just allow the completion handler to run and have it check what the result was.