Nonblocking I/O - HP Rp3440-4 - 9000 - 0 MB RAM Programmer's Manual

Nonblocking I/O

Sockets are created in blocking mode I/O by default. You can specify that
a socket be put in nonblocking mode by using the ioctl system call with
the FIOSNBIO request.
An example usage of this call is:
#include<sys/ioctl.h>
...
ioctl(s,FIOSNBIO,&arg);
arg is a pointer to int:
• When int equals 0, the socket is changed to blocking mode.
• When int equals 1, the socket is changed to nonblocking mode.
If a socket is in nonblocking mode, the following calls are affected:
If no messages are available to be received, recvfrom
recvfrom
returns the value -1 and the EWOULDBLOCK error.
This is also true for recv and read.
If there is no available message space for the message
sendto
to be transmitted, sendto returns the value -1 and the
EWOULDBLOCK error.
The O_NDELAY flag for fcntl(2) is also supported. If you use this flag
and there is no message available to be received on a recv, recvfrom, or
read call, the call returns immediately with the value of 0. If you use the
O_NONBLOCK flag, the call returns immediately with the value of -1
and the EAGAIN error. This is the same as returning an end-of-file
condition. This is also true for send , sendto, and write if there is not
enough buffer space to complete the send.
The O_NDELAY and O_NONBLOCK flags have precedence over the
FIOSNBIO flag. Setting both the O_DELAY and O_NONBLOCK flags is
not allowed.
Chapter 5
Advanced Topics for Internet Datagram Sockets
Nonblocking I/O
121