svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
poll(2)
poll(2) System Calls poll(2)
NAME
poll, ppoll - input/output multiplexing
SYNOPSIS
#include <poll.h>
int poll(struct pollfd * fds, nfds_t nfds, int timeout);
int ppoll(struct pollfd *restrict fds, nfds_t nfds,
const struct timespec *restrict timeout,
const sigset_t *restrict sigmask);
DESCRIPTION
The poll() function provides applications with a mechanism for multi‐
plexing input/output over a set of file descriptors. For each member of
the array pointed to by fds, poll() examines the given file descriptor
for the event(s) specified in events. The number of pollfd structures
in the fds array is specified by nfds. The poll() function identifies
those file descriptors on which an application can read or write data,
or on which certain events have occurred.
The fds argument specifies the file descriptors to be examined and the
events of interest for each file descriptor. It is a pointer to an ar‐
ray with one member for each open file descriptor of interest. The ar‐
ray's members are pollfd structures, which contain the following mem‐
bers:
int fd; /* file descriptor */
short events; /* requested events */
short revents; /* returned events */
The fd member specifies an open file descriptor and the events and
revents members are bitmasks constructed by a logical OR operation of
any combination of the following event flags:
POLLIN Data other than high priority data may be read without
blocking. For streams, this flag is set in revents even
if the message is of zero length.
POLLRDNORM Normal data (priority band equals 0) may be read without
blocking. For streams, this flag is set in revents even
if the message is of zero length.
POLLRDBAND Data from a non-zero priority band may be read without
blocking. For streams, this flag is set in revents even
if the message is of zero length.
POLLPRI High priority data may be received without blocking. For
streams, this flag is set in revents even if the message
is of zero length.
POLLOUT Normal data (priority band equals 0) may be written with‐
out blocking.
POLLWRNORM The same as POLLOUT.
POLLWRBAND Priority data (priority band > 0) may be written. This
event only examines bands that have been written to at
least once.
POLLERR An error has occurred on the device or stream. This flag
is only valid in the revents bitmask; it is not used in
the events member.
POLLHUP A hangup has occurred on the stream. This event and POLL‐
OUT are mutually exclusive; a stream can never be
writable if a hangup has occurred. However, this event
and POLLIN, POLLRDNORM, POLLRDBAND, or POLLPRI are not
mutually exclusive. This flag is only valid in the
revents bitmask; it is not used in the events member.
POLLNVAL The specified fd value does not belong to an open file.
This flag is only valid in the revents member; it is not
used in the events member.
If the value fd is less than 0, events is ignored and revents is set to
0 in that entry on return from poll().
The results of the poll() query are stored in the revents member in the
pollfd structure. Bits are set in the revents bitmask to indicate which
of the requested events are true. If none are true, none of the speci‐
fied bits are set in revents when the poll() call returns. The event
flags POLLHUP, POLLERR, and POLLNVAL are always set in revents if the
conditions they indicate are true; this occurs even though these flags
were not present in events.
If none of the defined events have occurred on any selected file de‐
scriptor, poll() waits at least timeout milliseconds for an event to
occur on any of the selected file descriptors. On a computer where mil‐
lisecond timing accuracy is not available, timeout is rounded up to the
nearest legal value available on that system. If the value timeout is
0, poll() returns immediately. If the value of timeout is −1, poll()
blocks until a requested event occurs or until the call is interrupted.
The poll() function is not affected by the O_NDELAY and O_NONBLOCK
flags.
The poll() function supports regular files, sockets, terminal and
pseudo-terminal devices, streams-based files, FIFOs and pipes. The be‐
havior of poll() on elements of fds that refer to other types of file
is unspecified.
A file descriptor for a socket that is listening for connections will
indicate that it is ready for reading, once connections are available.
A file descriptor for a socket that is connecting asynchronously will
indicate that it is ready for writing, once a connection has been es‐
tablished.
Regular files always poll() TRUE for reading and writing.
The relationship between poll() and ppoll() is analogous to the rela‐
tionship between select(3C) and pselect(3C): like pselect(), ppoll()
allows an application to safely wait until either a file descriptor be‐
comes ready or until a signal is caught.
Other than the difference in the timeout argument, the following
ppoll() call:
ready = ppoll(&fds, nfds, timeout, &sigmask);
is equivalent to atomically executing the following calls:
sigset_t origmask;
sigprocmask(SIG_SETMASK, &sigmask, &origmask);
ready = ppoll(&fds, nfds, timeout);
sigprocmask(SIG_SETMASK, &origmask, NULL);
If sigmask is not a null pointer, then the pselect() function replaces
the signal mask of the process by the set of signals pointed to by sig‐
mask before examining the descriptors, and restores the signal mask of
the process before returning.
The timeout argument specifies an upper limit on the amount of time
that ppoll() will block. This argument is a pointer to a structure of
the following form:
struct timespec {
time_t tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
};
If timeout is specified as NULL, ppoll() can block indefinitely.
RETURN VALUES
Upon successful completion, a non-negative value is returned. A posi‐
tive value indicates the total number of pollfd structures that have
been selected (that is, those for which the revents member is non-
zero). A value of 0 indicates that the call timed out and no file de‐
scriptors have been selected. Upon failure, −1 is returned and errno is
set to indicate the error.
ERRORS
The poll() and ppoll() functions will fail if:
EAGAIN Allocation of internal data structures failed, but the re‐
quest may be attempted again.
EFAULT Some argument points to an illegal address.
EINTR A signal was caught during the function call.
EINVAL The argument nfds is greater than {OPEN_MAX}, or one of the
fd members refers to a stream or multiplexer that is linked
(directly or indirectly) downstream from a multiplexer.
EINVAL An invalid timeout interval was specified.
The poll() and ppoll() functions may fail if:
ENOSYS One of the fd members is from a filesystem type for which
there is no poll() interface.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelAsync-Signal-
Safe _ StandardSee below.
Standard
See standards(7) for descriptions of the following standards:
tab() box; cw(2.2i) |cw(3.3i) lw(2.2i) |lw(3.3i) INTERFACESAPPLICABLE
STANDARDS _ poll()T{
POSIX.1-2001 through 2008,
SUS through SUSv4,
XPG4v2 through XPG7
T} _ ppoll()None
SEE ALSO
getmsg(2), getrlimit(2), Intro(2), putmsg(2), read(2), write(2), se‐
lect(3C), attributes(7), standards(7), chpoll(9E)
STREAMS Programming Guide
NOTES
Non-STREAMS drivers use chpoll(9E) to implement poll() on these de‐
vices.
HISTORY
The ppoll() function was added to Oracle Solaris in Solaris 11.0.0.
The poll() function has been included in all Sun and Oracle releases of
Solaris.
Oracle Solaris 11.4 14 May 2025 poll(2)