HP X.25/9000 Programmer's Guide

58 Chapter4

Sending and Receiving Data

Using Nonblocking I/O

Although sockets are created in blocking I/O mode by default, you can

specify that a socket be put in nonblocking I/O mode using the

ioctl(FIOSNBIO) call as shown below. The behavior of many system

calls changes when the socket is in nonblocking mode. These differences

in behaviour are also described in this section.

The ioctl(FIOSNBIO) call

Use the ioctl(FIOSNBIO) call to set a socket to blocking or nonblocking

I/O mode.

Syntax for ioctl(FIOSNBIO)

The syntax for the ioctl(FIOSNBIO) system call and its parameters are

described below.

#include <x25/x25ioctls.h>

int err;

int sd, arg;

err = ioctl(sd, FIOSNBIO, &arg);

sd Socket descriptor for a VC socket.

FIOSNBIO Controls whether the socket is set to blocking or nonblocking I/O mode.

This is speciﬁed by the value in

arg

arg Speciﬁes the socket’s operating mode. If the value in

arg

is 0, the socket

is in blocking mode. If the value in

arg

is 1, the socket is in nonblocking

mode. Sockets are in blocking mode by default.

err On successful completion,

err

is set to 0. Otherwise, a value of –1 is

returned and errno is set to indicate the error.

Nonblocking Behavior of System Calls

The behavior of many system calls changes when the socket is in

nonblocking mode. The system calls of primary importance to X.25

programmers are the accept() and connect(), send() and recv(),

read() and write(), and ioctl() calls. These differences in behavior

36960-90061.bk Page 58 Friday, November 10, 2000 3:42 PM