are there any ways to use send or recv temporarily in blocking mode when the socket is set non-blocking

Question

if a socket is set non-blocking,

but at a certain moment, I want to use send or recv with this socket in blocking mode,

can I temporarily sent it as blocking mode and then recover to non-blocking.

if so, how about the other way around? use send or recv temporarily in non-blocking mode if the socket is in blocking mode?

thanks!

score 3 · Answer 1 · answered Jun 14 '13 at 11:53

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You can use fcntl() with the O_NONBLOCK flag.

Use it to set the socket the blocking mode, send(or recv) your data and use fcntl again to set to the socket the non-blocking mode.

answered Jun 14 '13 at 11:53

nouney

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score 2 · Answer 2 · answered Jun 14 '13 at 11:54

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can I temporarily sent it as blocking mode and then recover to non-blocking.

Yes, of course, just use FIONBIO the other way round.

if so, how about the other way around? use send or recv temporarily in non-blocking mode if the socket is in blocking mode?

Yes, of course. There are two ways to do that: with FIONBIO or with the MSG_DONTWAIT flag to recv().

answered Jun 14 '13 at 11:54

user207421

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@misteryes Look at [this question](http://stackoverflow.com/questions/1150635/unix-nonblocking-i-o-o-nonblock-vs-fionbio) about FIONBIO and O_NONBLOCK – nouney Jun 14 '13 at 12:07
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Ｉ don't get it when you say FIONBIO can set a non-blocking socket temporarily to blocking mode. – misteryes Jun 14 '13 at 12:09
It's not temporarily with FIONBIO, it acts like O_NONBLOCK. that means you have to call `ioctl()` before and after the `recv()`/`send()`, just like `fcntl()` (which is a POSIX function, so you should use it instead of `ioctl()`) – nouney Jun 14 '13 at 12:40
I don't see what there is not to get. FIONBIO is used to set or clear non-blocking mode. Or O_NONBLOCK. – user207421 Jun 14 '13 at 20:04

score 1 · Answer 3 · answered Jun 15 '13 at 14:55

You could change the mode, or you could just use select() or epoll() to detect when a socket is readable/writable before performing a recv/send() that would normally block, or to simulate blocking behavior by reading/sending in a loop while the intended data is still pending.

score 0 · Answer 4 · answered Jun 14 '13 at 12:30

Well, as already has been said, you can of course change the state whenever you want with the fcntl() call. However I don't really understand the requirement, because when you implement a non blocking algorithm, you can of course make it appear as if it were blocking by simply looping. And you will need a protocoll anyway, so this seems to me as if you were relying on some particular behaviour.

are there any ways to use send or recv temporarily in blocking mode when the socket is set non-blocking

4 Answers4