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.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
.. c:namespace:: MC
.. _request-func-poll:
**************
request poll()
**************
Name
====
request-poll - Wait for some event on a file descriptor
Synopsis
========
.. code-block:: c
#include <sys/poll.h>
.. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout )
Arguments
=========
``ufds``
List of file descriptor events to be watched
``nfds``
Number of file descriptor events at the \*ufds array
``timeout``
Timeout to wait for events
Description
===========
With the :c:func:`poll()` function applications can wait
for a request to complete.
On success :c:func:`poll()` returns the number of file
descriptors that have been selected (that is, file descriptors for which the
``revents`` field of the respective struct :c:type:`pollfd`
is non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents``
when the request was completed. When the function times out it returns
a value of zero, on failure it returns -1 and the ``errno`` variable is
set appropriately.
Attempting to poll for a request that is not yet queued will
set the ``POLLERR`` flag in ``revents``.
Return Value
============
On success, :c:func:`poll()` returns the number of
structures which have non-zero ``revents`` fields, or zero if the call
timed out. On error -1 is returned, and the ``errno`` variable is set
appropriately:
``EBADF``
One or more of the ``ufds`` members specify an invalid file
descriptor.
``EFAULT``
``ufds`` references an inaccessible memory area.
``EINTR``
The call was interrupted by a signal.
``EINVAL``
The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use
``getrlimit()`` to obtain this value.
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