18c2ecf20Sopenharmony_ci.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later 28c2ecf20Sopenharmony_ci.. c:namespace:: MC 38c2ecf20Sopenharmony_ci 48c2ecf20Sopenharmony_ci.. _request-func-poll: 58c2ecf20Sopenharmony_ci 68c2ecf20Sopenharmony_ci************** 78c2ecf20Sopenharmony_cirequest poll() 88c2ecf20Sopenharmony_ci************** 98c2ecf20Sopenharmony_ci 108c2ecf20Sopenharmony_ciName 118c2ecf20Sopenharmony_ci==== 128c2ecf20Sopenharmony_ci 138c2ecf20Sopenharmony_cirequest-poll - Wait for some event on a file descriptor 148c2ecf20Sopenharmony_ci 158c2ecf20Sopenharmony_ciSynopsis 168c2ecf20Sopenharmony_ci======== 178c2ecf20Sopenharmony_ci 188c2ecf20Sopenharmony_ci.. code-block:: c 198c2ecf20Sopenharmony_ci 208c2ecf20Sopenharmony_ci #include <sys/poll.h> 218c2ecf20Sopenharmony_ci 228c2ecf20Sopenharmony_ci.. c:function:: int poll( struct pollfd *ufds, unsigned int nfds, int timeout ) 238c2ecf20Sopenharmony_ci 248c2ecf20Sopenharmony_ciArguments 258c2ecf20Sopenharmony_ci========= 268c2ecf20Sopenharmony_ci 278c2ecf20Sopenharmony_ci``ufds`` 288c2ecf20Sopenharmony_ci List of file descriptor events to be watched 298c2ecf20Sopenharmony_ci 308c2ecf20Sopenharmony_ci``nfds`` 318c2ecf20Sopenharmony_ci Number of file descriptor events at the \*ufds array 328c2ecf20Sopenharmony_ci 338c2ecf20Sopenharmony_ci``timeout`` 348c2ecf20Sopenharmony_ci Timeout to wait for events 358c2ecf20Sopenharmony_ci 368c2ecf20Sopenharmony_ciDescription 378c2ecf20Sopenharmony_ci=========== 388c2ecf20Sopenharmony_ci 398c2ecf20Sopenharmony_ciWith the :c:func:`poll()` function applications can wait 408c2ecf20Sopenharmony_cifor a request to complete. 418c2ecf20Sopenharmony_ci 428c2ecf20Sopenharmony_ciOn success :c:func:`poll()` returns the number of file 438c2ecf20Sopenharmony_cidescriptors that have been selected (that is, file descriptors for which the 448c2ecf20Sopenharmony_ci``revents`` field of the respective struct :c:type:`pollfd` 458c2ecf20Sopenharmony_ciis non-zero). Request file descriptor set the ``POLLPRI`` flag in ``revents`` 468c2ecf20Sopenharmony_ciwhen the request was completed. When the function times out it returns 478c2ecf20Sopenharmony_cia value of zero, on failure it returns -1 and the ``errno`` variable is 488c2ecf20Sopenharmony_ciset appropriately. 498c2ecf20Sopenharmony_ci 508c2ecf20Sopenharmony_ciAttempting to poll for a request that is not yet queued will 518c2ecf20Sopenharmony_ciset the ``POLLERR`` flag in ``revents``. 528c2ecf20Sopenharmony_ci 538c2ecf20Sopenharmony_ciReturn Value 548c2ecf20Sopenharmony_ci============ 558c2ecf20Sopenharmony_ci 568c2ecf20Sopenharmony_ciOn success, :c:func:`poll()` returns the number of 578c2ecf20Sopenharmony_cistructures which have non-zero ``revents`` fields, or zero if the call 588c2ecf20Sopenharmony_citimed out. On error -1 is returned, and the ``errno`` variable is set 598c2ecf20Sopenharmony_ciappropriately: 608c2ecf20Sopenharmony_ci 618c2ecf20Sopenharmony_ci``EBADF`` 628c2ecf20Sopenharmony_ci One or more of the ``ufds`` members specify an invalid file 638c2ecf20Sopenharmony_ci descriptor. 648c2ecf20Sopenharmony_ci 658c2ecf20Sopenharmony_ci``EFAULT`` 668c2ecf20Sopenharmony_ci ``ufds`` references an inaccessible memory area. 678c2ecf20Sopenharmony_ci 688c2ecf20Sopenharmony_ci``EINTR`` 698c2ecf20Sopenharmony_ci The call was interrupted by a signal. 708c2ecf20Sopenharmony_ci 718c2ecf20Sopenharmony_ci``EINVAL`` 728c2ecf20Sopenharmony_ci The ``nfds`` value exceeds the ``RLIMIT_NOFILE`` value. Use 738c2ecf20Sopenharmony_ci ``getrlimit()`` to obtain this value. 74