1.\" 2.\" Copyright (c) 2005 Apple Computer, Inc. All rights reserved. 3.\" 4.\" @APPLE_LICENSE_HEADER_START@ 5.\" 6.\" This file contains Original Code and/or Modifications of Original Code 7.\" as defined in and that are subject to the Apple Public Source License 8.\" Version 2.0 (the 'License'). You may not use this file except in 9.\" compliance with the License. Please obtain a copy of the License at 10.\" http://www.opensource.apple.com/apsl/ and read it before using this 11.\" file. 12.\" 13.\" The Original Code and all software distributed under the License are 14.\" distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER 15.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, 16.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, 17.\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. 18.\" Please see the License for the specific language governing rights and 19.\" limitations under the License. 20.\" 21.\" @APPLE_LICENSE_HEADER_END@ 22.\" 23.\" 24.\" Copyright (c) 1996 Charles M. Hannum. All rights reserved. 25.\" 26.\" Redistribution and use in source and binary forms, with or without 27.\" modification, are permitted provided that the following conditions 28.\" are met: 29.\" 1. Redistributions of source code must retain the above copyright 30.\" notice, this list of conditions and the following disclaimer. 31.\" 2. Redistributions in binary form must reproduce the above copyright 32.\" notice, this list of conditions and the following disclaimer in the 33.\" documentation and/or other materials provided with the distribution. 34.\" 3. All advertising materials mentioning features or use of this software 35.\" must display the following acknowledgement: 36.\" This product includes software developed by Charles M. Hannum. 37.\" 4. The name of the author may not be used to endorse or promote products 38.\" derived from this software without specific prior written permission. 39.\" 40.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 41.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 42.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 43.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 44.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 45.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 46.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 47.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 48.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 49.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 50.\" 51.Dd March 18, 2015 52.Dt POLL 2 53.Os 54.Sh NAME 55.Nm poll 56.Nd synchronous I/O multiplexing 57.Sh SYNOPSIS 58.In poll.h 59.Ft int 60.Fo poll 61.Fa "struct pollfd fds[]" 62.Fa "nfds_t nfds" 63.Fa "int timeout" 64.Fc 65.Sh DESCRIPTION 66.Fn poll 67examines a set of file descriptors 68to see if some of them are ready for I/O 69or if certain events have occurred on them. 70The 71.Fa fds 72argument is a pointer to an array of pollfd structures, 73as defined in 74.Aq Pa poll.h 75(shown below). The 76.Fa nfds 77argument specifies the size of the 78.Fa fds 79array. 80.Bd -literal 81struct pollfd { 82 int fd; /* file descriptor */ 83 short events; /* events to look for */ 84 short revents; /* events returned */ 85}; 86.Ed 87.Pp 88The fields of 89.Fa struct pollfd 90are as follows: 91.Bl -tag -width XXXPOLLWRNORM 92.It fd 93File descriptor to poll. 94.It events 95Events to poll for. (See below.) 96.It revents 97Events which may occur or have occurred. (See below.) 98.El 99.Pp 100The event bitmasks in 101.Fa events 102and 103.Fa revents 104have the following bits: 105.Bl -tag -width XXXPOLLWRNORM 106.\" =========== 107.It POLLERR 108An exceptional condition has occurred on the device or socket. 109This flag is output only, and ignored if present in the input 110.Fa events 111bitmask. 112.\" =========== 113.It POLLHUP 114The device or socket has been disconnected. 115This flag is output only, 116and ignored if present in the input 117.Fa events 118bitmask. 119Note that POLLHUP and POLLOUT 120are mutually exclusive and should never be present in the 121.Fa revents 122bitmask at the same time. 123.\" =========== 124.It POLLIN 125Data other than high priority data may be read without blocking. 126This is equivalent to ( POLLRDNORM | POLLRDBAND ). 127.\" =========== 128.It POLLNVAL 129The file descriptor is not open. 130This flag is output only, and ignored if present in the input 131.Fa events 132bitmask. 133.\" =========== 134.It POLLOUT 135Normal data may be written without blocking. 136This is equivalent to POLLWRNORM. 137.\" =========== 138.It POLLPRI 139High priority data may be read without blocking. 140.\" =========== 141.It POLLRDBAND 142Priority data may be read without blocking. 143.\" =========== 144.It POLLRDNORM 145Normal data may be read without blocking. 146.\" =========== 147.It POLLWRBAND 148Priority data may be written without blocking. 149.\" =========== 150.It POLLWRNORM 151Normal data may be written without blocking. 152.El 153.Pp 154The distinction between normal, priority, and high-priority data 155is specific to particular file types or devices. 156.Pp 157If 158.Fa timeout 159is greater than zero, 160it specifies a maximum interval (in milliseconds) 161to wait for any file descriptor to become ready. 162If 163.Fa timeout 164is zero, then 165.Fn poll 166will return without blocking. If the value of 167.Fa timeout 168is -1, the poll blocks indefinitely. 169.Sh RETURN VALUES 170.Fn poll 171returns the number of descriptors that are ready for I/O, 172or -1 if an error occurred. 173If the time limit expires, 174.Fn poll 175returns 0. 176If 177.Fn poll 178returns with an error, 179including one due to an interrupted call, 180the 181.Fa fds 182array will be unmodified and the global variable 183.Va errno 184will be set to indicate the error. 185.Sh ERRORS 186.Fn poll 187will fail if: 188.Bl -tag -width Er 189.\" =========== 190.It Bq Er EAGAIN 191Allocation of internal data structures fails. 192A subsequent request may succeed. 193.\" =========== 194.It Bq Er EFAULT 195.Fa Fds 196points outside the process's allocated address space. 197.\" =========== 198.It Bq Er EINTR 199A signal is delivered before the time limit expires 200and before any of the selected events occurs. 201.\" =========== 202.It Bq Er EINVAL 203The 204.Fa nfds 205argument is greater than OPEN_MAX or the 206.Fa timeout 207argument is less than -1. 208.El 209.Sh BUGS 210The 211.Fn poll 212system call currently does not support devices. 213.Sh SEE ALSO 214.Xr accept 2 , 215.Xr connect 2 , 216.Xr connectx 2 , 217.Xr kevent 2 , 218.Xr read 2 , 219.Xr recv 2 , 220.Xr select 2 , 221.Xr send 2 , 222.Xr write 2 223.Sh HISTORY 224The 225.Fn poll 226function call appeared in 227.At V . 228