How can I tell if a socket buffer is full?

Question

How can I tell if a read socket buffer is full or a write socket buffer is empty?

Is there a way I can get the status of a socket buffer without a system call?

UPDATE: How about this: I'd like to get a callback or signal when either the read socket buffer is full or the write socket buffer is empty. This way I can stop processing to allow more I/O to occur on the wire, since being I/O bound is always an issue when sending data on the wire.

The select() call is how you check if the read buffer has something in it. Not when it is full (I think).

Answer 1

Poll the file descriptor with select and a zero timeout - if select says it's writeable, the send buffer isn't full.

(Oh... without a system call. No, there isn't.)

Addendum:

In response to your updated question, you can use two ioctls on the TCP socket: SIOCINQ returns the amount of unread data in the recieve buffer, and SIOCOUTQ returns the amount of unsent data in the send queue. I don't believe there's any asynchronous event notification for these though, which will leave you having to poll.