NAME

poll.h — definitions for the poll() function

SYNOPSIS

#include <poll.h>

DESCRIPTION

The <poll.h> header shall define the pollfd structure, which shall include at least the following members:

int    fd       The following descriptor being polled.
short  events   The input event flags (see below).
short  revents  The output event flags (see below).

The <poll.h> header shall define the following type through typedef:

nfds_t

An unsigned integer type used for the number of file descriptors.

The implementation shall support one or more programming environments in which the width of nfds_t is no greater than the width of type long. The names of these programming environments can be obtained using the confstr() function or the getconf utility.

The <poll.h> header shall define the sigset_t type as described in <signal.h>.

The <poll.h> header shall define the timespec structure as described in <time.h>.

The <poll.h> header shall define the following symbolic constants, zero or more of which may be OR'ed together to form the events or revents members in the pollfd structure:

POLLIN

Data other than high-priority data may be read without blocking.

POLLRDNORM

Normal data may be read without blocking.

POLLRDBAND

Priority data may be read without blocking.

POLLPRI

High priority data may be read without blocking.

POLLOUT

Normal data may be written without blocking.

POLLWRNORM

Equivalent to POLLOUT.

POLLWRBAND

Priority data may be written.

POLLERR

An error has occurred (revents only).

POLLHUP

Device has been disconnected (revents only).

POLLNVAL

Invalid fd member (revents only).

The significance and semantics of normal, priority, and high-priority data are file and device-specific.

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

int   poll(struct pollfd [], nfds_t, int);
int   ppoll(struct pollfd [], nfds_t, const struct timespec *restrict,
          const sigset_t *restrict);

Inclusion of the <poll.h> header may make visible all symbols from the headers <signal.h> and <time.h>.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

XSH confstr, poll

XCU getconf

CHANGE HISTORY

First released in Issue 4, Version 2.

Issue 6

The description of the symbolic constants is updated to match the poll() function.

Text related to STREAMS has been moved to the poll() reference page.

A note is added to the DESCRIPTION regarding the significance and semantics of normal, priority, and high-priority data.

Issue 7

The <poll.h> header is moved from the XSI option to the Base.

Issue 8

Austin Group Defect 1263 is applied, adding ppoll(), requiring <poll.h> to define sigset_t and struct timespec, and allowing <poll.h> to make visible all symbols from <signal.h> and <time.h>.