.\" .\" Copyright (c) 2005 Apple Computer, Inc. All rights reserved. .\" .\" @APPLE_LICENSE_OSREFERENCE_HEADER_START@ .\" .\" This file contains Original Code and/or Modifications of Original Code .\" as defined in and that are subject to the Apple Public Source License .\" Version 2.0 (the "License"). You may not use this file except in .\" compliance with the License. The rights granted to you under the .\" License may not be used to create, or enable the creation or .\" redistribution of, unlawful or unlicensed copies of an Apple operating .\" system, or to circumvent, violate, or enable the circumvention or .\" violation of, any terms of an Apple operating system software license .\" agreement. .\" .\" Please obtain a copy of the License at .\" http://www.opensource.apple.com/apsl/ and read it before using this .\" file. .\" .\" The Original Code and all software distributed under the License are .\" distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER .\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, .\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, .\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. .\" Please see the License for the specific language governing rights and .\" limitations under the License. .\" .\" @APPLE_LICENSE_OSREFERENCE_HEADER_END@ .\" .\" .\" Copyright (c) 1996 Charles M. Hannum. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by Charles M. Hannum. .\" 4. The name of the author may not be used to endorse or promote products .\" derived from this software without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd February 27, 2005 .Dt POLL 2 .Os .Sh NAME .Nm poll .Nd synchronous I/O multiplexing .Sh SYNOPSIS .In poll.h .Ft int .Fn poll "struct pollfd *fds" "nfds_t nfds" "int timeout" .Sh DESCRIPTION .Fn Poll examines a set of file descriptors to see if some of them are ready for I/O or if certain events have occurred on them. The .Fa fds argument is a pointer to an array of pollfd structures as defined in .Aq Pa poll.h (shown below). The .Fa nfds argument determines the size of the .Fa fds array. .Bd -literal struct pollfd { int fd; /* file descriptor */ short events; /* events to look for */ short revents; /* events returned */ }; .Ed .Pp The fields of .Fa struct pollfd are as follows: .Bl -tag -width XXXrevents .It fd File descriptor to poll. .It events Events to poll for. (See below.) .It revents Events which may occur or have occurred. (See below.) .El .Pp The event bitmasks in .Fa events and .Fa revents have the following bits: .Bl -tag -width XXXPOLLWRNORM .It POLLIN Data other than high priority data may be read without blocking. This is equivalent to ( POLLRDNORM | POLLRDBAND ). .It POLLRDNORM Normal data may be read without blocking. .It POLLRDBAND Priority data may be read without blocking. .It POLLPRI High priority data may be read without blocking. .It POLLOUT .It POLLWRNORM Normal data may be written without blocking. .It POLLWRBAND Priority data may be written without blocking. .It POLLERR An exceptional condition has occurred on the device or socket. This flag is output only, and ignored if present in the input .Fa events bitmask. .It POLLHUP The device or socket has been disconnected. This flag is output only, and ignored if present in the input .Fa events bitmask. Note that POLLHUP and POLLOUT are mutually exclusive and should never be present in the .Fa revents bitmask at the same time. .It POLLNVAL The file descriptor is not open. This flag is output only, and ignored if present in the input .Fa events bitmask. .El .Pp The distinction between normal, priority, and high-priority data is file type or device specific. .Pp If .Fa timeout is greater than zero, it specifies a maximum interval to wait for any file descriptor to become ready, in milliseconds. If .Fa timeout is zero, then .Fn poll will return without blocking. If the value of .Fa timeout is -1, the poll blocks indefinitely. .Sh RETURN VALUES .Fn Poll returns the number of descriptors that are ready for I/O, or -1 if an error occured. If the time limit expires, .Fn poll returns 0. If .Fn poll returns with an error, including one due to an interrupted call, the .Fa fds array will be unmodified. .Sh ERRORS An error return from .Fn poll indicates: .Bl -tag -width Er .It Bq Er EFAULT .Fa Fds points outside the process's allocated address space. .It Bq Er EINTR A signal was delivered before the time limit expired and before any of the selected events occurred. .It Bq Er EINVAL The .Fa nfds argument is greater than OPEN_MAX, or the .Fa timeout argument is less than -1. .El .Sh BUGS The .Fn poll system call currently does not support devices. .Sh SEE ALSO .Xr accept 2 , .Xr connect 2 , .Xr kevent 2 , .Xr read 2 , .Xr recv 2 , .Xr select 2 , .Xr send 2 , .Xr write 2 .Sh HISTORY The .Fn poll function call appeared in .At V .