poll.2 (2010 09)

ManualsBrandsHP ManualsSoftwareHP-UX Manpages

poll(2) poll(2)

NAME

poll - monitor I/O conditions on multiple ﬁle descriptors

SYNOPSIS

#include <poll.h>

int poll(

struct pollfd fds[],

nfds_t nfds,

int timeout);

DESCRIPTION

poll() provides a general mechanism for reporting I/O conditions associated with a set of ﬁle descrip-

tors and for waiting until one or more speciﬁed conditions becomes true. Speciﬁed conditions include the

ability to read or write data without blocking, and error conditions.

Arguments

fds Points to an array of

pollfd structures, one for each ﬁle descriptor of interest.

nfds Speciﬁes the number of

pollfd structures in the fds array.

timeout Speciﬁes the maximum length of time (in milliseconds) to wait for at least one of the

speciﬁed conditions to occur.

Each

pollfd structure includes the following members:

int fd File descriptor

short events Requested conditions

short revents Reported conditions

The

fd member of each pollfd structure speciﬁes an open ﬁle descriptor. The poll()

function uses

the

events member to determine what conditions to report for this ﬁle descriptor. If one or more of

these conditions is true, poll() sets the associated revents member.

poll() ignores any pollfd structure whose fd member is negative. If the fd member of all

pollfd structures is negative, poll() returns 0 and has no other results.

The

events and revents members of the pollfd structure are bit masks. The calling process sets

the events bit mask, and poll() sets the revents bit masks. These bit masks contain ORed com-

binations of condition ﬂags. The following condition ﬂags are deﬁned:

POLLIN Data can be read without blocking. For streams, this ﬂag means that a mes-

sage that is not high priority is at the front of the stream head read queue.

This message can be of zero length.

POLLNORM Synonym for POLLIN

POLLPRI A high priority message is available. For streams, this message can be of zero

length.

POLLOUT Data can be written without blocking. For streams, this ﬂag speciﬁes that nor-

mal data (not high priority or priority band > 0) can be written without being

blocked by ﬂow control. This ﬂag is not used for high priority data, because it

can be written even if the stream is ﬂow controlled.

POLLERR An error has occurred on the ﬁle descriptor.

POLLHUP The device has been disconnected. For streams, this ﬂag in revents is

mutually exclusive with POLLOUT, since a stream cannot be written to after a

hangup occurs. This ﬂag and POLLIN, POLLPRI, POLLRDNORM, POLLRD-

BAND, and POLLMSG are not mutually exclusive.

POLLNVAL fd is not a valid ﬁle descriptor.

POLLRDNORM A non-priority message is available. For streams, this ﬂag means that a nor-

mal message (not high priority or priority band > 0) is at the front of the

stream head read queue. This message can be of zero length.

POLLRDBAND A priority message (priority band > 0) is at the front of the stream head read

queue. This message can be read without blocking. The message can be of

zero length.

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (4 pages)

PAGE 1
poll(2) poll(2) NAME poll - monitor I/O conditions on multiple file descriptors SYNOPSIS #include int poll( struct pollfd fds[], nfds_t nfds, int timeout); DESCRIPTION poll() provides a general mechanism for reporting I/O conditions associated with a set of file descriptors and for waiting until one or more specified conditions becomes true. Specified conditions include the ability to read or write data without blocking, and error conditions.
PAGE 2
poll(2) poll(2) POLLWRNORM Same as POLLOUT POLLWRBAND Priority data (priority band > 0) can be written without being blocked by flow control. Only previously written bands are checked. POLLMSG A M_SIG or M_PCSIG message specifying SIGPOLL has reached the front of the stream head read queue. The conditions indicated by POLLNORM and POLLOUT are true if and only if at least one byte of data can be read or written without blocking.
PAGE 3
poll(2) poll(2) fds.fd = 0; fds.events = POLLNORM; poll(&fds, 1, -1); Wait for input on ifd1 and ifd2, output on ofd, giving up after 10 seconds: #include struct pollfd fds[3]; int ifd1, ifd2, ofd, count; fds[0].fd = ifd1; fds[0].events = POLLNORM; fds[1].fd = ifd2; fds[1].events = POLLNORM; fds[2].fd = ofd; fds[2].events = POLLOUT; count = poll(fds, 3, 10000); if (count == -1) { perror("poll failed"); exit(1); } if (count==0) printf("No data for reading or writing\n"); if (fds[0].
PAGE 4
(Notes) A (Notes) pA 4 Hewlett-Packard Company −1− HP-UX 11i Version 3: September 2010