First of all, we have to distinguish the following IO model:
Blocking IO
Classmate A is waiting for the letter and has been waiting by the mailbox
Non-blocking IO
Classmate B waits for the letter, check the mailbox every other time, wait for the letter to come
Asynchronous IO
Classmate C told classmate E that he would tell me after he got a letter, and then classmate C flew a plane
( as long as he waited, it was all synchronized IO )
IO multiplexing
Classmate F is from a wealthy family and has a bunch of mailboxes.
Classmate F asks classmate G to see someone sending a letter and tells him (the kernel select function, if it is the epoll function, is more efficient),
then F waits for each mailbox and waits for someone to load the letter Into the mailbox. (Recv function)
Signal drive IO
H students to the students I say, it was to deliver the letter to the play signal , the signal went to see H-mail and other letter.
