.. 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 .. 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.