HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)

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STANDARD Printed by: Nora Chuang [nchuang] STANDARD

/build/1111/BRICK/man2/!!!intro.2

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poll(2) poll(2)

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. The exception is regular ﬁles, which always poll true for POLLNORM

and POLLOUT. Also, streams return POLLNORM in revents even if the available message is of zero

length.

The condition ﬂags POLLERR, POLLHUP, and POLLNVAL are always set in revents if the conditions

they indicate are true for the speciﬁed ﬁle descriptor, whether or not these ﬂags are set in events.

For each call to poll(), the set of reportable conditions for each ﬁle descriptor consists of those conditions

that are always reported, together with any further conditions for which ﬂags are set in events. If any

reportable condition is true for any ﬁle descriptor, poll() returns with ﬂags set in revents for each

true condition for that ﬁle descriptor.

If no reportable condition is true for any of the ﬁle descriptors, poll() waits up to timeout milliseconds

for a reportable condition to become true. If, in that time interval, a reportable condition becomes true for

any of the ﬁle descriptors, poll() reports the condition in the ﬁle descriptor’s associated revents

member and returns. If no reportable condition becomes true,

poll() returns without setting any

revents bit masks.

If the timeout parameter is a value of −1, poll() does not return until at least one speciﬁed event has

occurred. If the value of the timeout parameter is 0, poll() does not wait for an event to occur but

returns immediately, even if no speciﬁed event has occurred. The behavior of poll() is not affected by

whether the

O_NONBLOCK ﬂag is set on any of the speciﬁed ﬁle descriptors.

RETURN VALUES

Upon successful completion, poll() returns a nonnegative value. If the call returns 0, poll() has

timed out and has not set any of the

revents bit masks. A positive value indicates the number of ﬁle

descriptors for which poll() has set the revents bit mask. If poll() fails, it returns −1 and sets

errno to indicate the error.

ERRORS

poll() fails if any of the following conditions are encountered:

[EAGAIN] Allocation of internal data structures failed. A later call to poll() may complete

successfully.

[EINTR] A signal was delivered before any of the selected for conditions occurred or before the

time limit expired.

[EINVAL] timeout is a negative number other than −1.

[EFAULT] The fds parameter in conjunction with the nfds parameter addresses a location out-

side of the allocated address space of the process. Reliable detection of this error is

implementation-dependent.

EXAMPLES

Wait for input on ﬁle descriptor 0:

#include <poll.h>

struct pollfd fds;

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 <poll.h>

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;

Section 2−−214 − 2 − HP-UX Release 11i: December 2000

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