227 lines
6.3 KiB
Groff
227 lines
6.3 KiB
Groff
.\"
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.\" Copyright (c) 2005 Apple Computer, Inc. All rights reserved.
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.\"
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.\" @APPLE_LICENSE_HEADER_START@
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.\"
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.\" This file contains Original Code and/or Modifications of Original Code
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.\" as defined in and that are subject to the Apple Public Source License
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.\" Version 2.0 (the 'License'). You may not use this file except in
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.\" compliance with the License. Please obtain a copy of the License at
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.\" http://www.opensource.apple.com/apsl/ and read it before using this
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.\" file.
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.\"
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.\" The Original Code and all software distributed under the License are
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.\" distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
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.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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.\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
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.\" Please see the License for the specific language governing rights and
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.\" limitations under the License.
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.\"
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.\" @APPLE_LICENSE_HEADER_END@
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.\"
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.\"
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.\" Copyright (c) 1996 Charles M. Hannum. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by Charles M. Hannum.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd March 18, 2015
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.Dt POLL 2
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.Os
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.Sh NAME
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.Nm poll
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.Nd synchronous I/O multiplexing
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.Sh SYNOPSIS
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.In poll.h
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.Ft int
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.Fo poll
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.Fa "struct pollfd fds[]"
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.Fa "nfds_t nfds"
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.Fa "int timeout"
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.Fc
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.Sh DESCRIPTION
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.Fn poll
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examines a set of file descriptors
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to see if some of them are ready for I/O
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or if certain events have occurred on them.
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The
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.Fa fds
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argument is a pointer to an array of pollfd structures,
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as defined in
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.Aq Pa poll.h
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(shown below). The
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.Fa nfds
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argument specifies the size of the
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.Fa fds
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array.
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.Bd -literal
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struct pollfd {
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int fd; /* file descriptor */
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short events; /* events to look for */
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short revents; /* events returned */
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};
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.Ed
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.Pp
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The fields of
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.Fa struct pollfd
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are as follows:
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.Bl -tag -width XXXPOLLWRNORM
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.It fd
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File descriptor to poll.
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.It events
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Events to poll for. (See below.)
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.It revents
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Events which may occur or have occurred. (See below.)
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.El
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.Pp
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The event bitmasks in
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.Fa events
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and
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.Fa revents
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have the following bits:
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.Bl -tag -width XXXPOLLWRNORM
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.\" ===========
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.It POLLERR
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An exceptional condition has occurred on the device or socket.
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This flag is output only, and ignored if present in the input
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.Fa events
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bitmask.
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.\" ===========
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.It POLLHUP
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The device or socket has been disconnected.
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This flag is output only,
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and ignored if present in the input
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.Fa events
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bitmask.
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Note that POLLHUP and POLLOUT
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are mutually exclusive and should never be present in the
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.Fa revents
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bitmask at the same time.
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.\" ===========
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.It POLLIN
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Data other than high priority data may be read without blocking.
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This is equivalent to ( POLLRDNORM | POLLRDBAND ).
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.\" ===========
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.It POLLNVAL
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The file descriptor is not open.
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This flag is output only, and ignored if present in the input
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.Fa events
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bitmask.
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.\" ===========
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.It POLLOUT
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Normal data may be written without blocking.
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This is equivalent to POLLWRNORM.
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.\" ===========
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.It POLLPRI
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High priority data may be read without blocking.
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.\" ===========
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.It POLLRDBAND
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Priority data may be read without blocking.
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.\" ===========
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.It POLLRDNORM
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Normal data may be read without blocking.
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.\" ===========
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.It POLLWRBAND
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Priority data may be written without blocking.
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.\" ===========
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.It POLLWRNORM
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Normal data may be written without blocking.
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.El
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.Pp
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The distinction between normal, priority, and high-priority data
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is specific to particular file types or devices.
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.Pp
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If
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.Fa timeout
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is greater than zero,
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it specifies a maximum interval (in milliseconds)
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to wait for any file descriptor to become ready.
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If
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.Fa timeout
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is zero, then
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.Fn poll
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will return without blocking. If the value of
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.Fa timeout
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is -1, the poll blocks indefinitely.
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.Sh RETURN VALUES
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.Fn poll
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returns the number of descriptors that are ready for I/O,
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or -1 if an error occurred.
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If the time limit expires,
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.Fn poll
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returns 0.
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If
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.Fn poll
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returns with an error,
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including one due to an interrupted call,
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the
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.Fa fds
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array will be unmodified and the global variable
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.Va errno
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will be set to indicate the error.
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.Sh ERRORS
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.Fn poll
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will fail if:
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.Bl -tag -width Er
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.\" ===========
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.It Bq Er EAGAIN
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Allocation of internal data structures fails.
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A subsequent request may succeed.
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.\" ===========
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.It Bq Er EFAULT
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.Fa Fds
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points outside the process's allocated address space.
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.\" ===========
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.It Bq Er EINTR
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A signal is delivered before the time limit expires
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and before any of the selected events occurs.
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.\" ===========
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.It Bq Er EINVAL
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The
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.Fa nfds
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argument is greater than OPEN_MAX or the
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.Fa timeout
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argument is less than -1.
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.El
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.Sh BUGS
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The
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.Fn poll
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system call currently does not support devices.
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.Sh SEE ALSO
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.Xr accept 2 ,
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.Xr connect 2 ,
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.Xr connectx 2 ,
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.Xr kevent 2 ,
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.Xr read 2 ,
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.Xr recv 2 ,
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.Xr select 2 ,
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.Xr send 2 ,
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.Xr write 2
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.Sh HISTORY
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The
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.Fn poll
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function call appeared in
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.At V .
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