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/*---------------------------------------------------------------------------*\
$Id$
NAME
poll - select(2)-based poll() emulation function for BSD systems.
SYNOPSIS
#include "poll.h"
struct pollfd
{
int fd;
short events;
short revents;
}
int poll (struct pollfd *pArray, unsigned long n_fds, int timeout)
DESCRIPTION
This file, and the accompanying "poll.h", implement the System V
poll(2) system call for BSD systems (which typically do not provide
poll()). Poll() provides a method for multiplexing input and output
on multiple open file descriptors; in traditional BSD systems, that
capability is provided by select(). While the semantics of select()
differ from those of poll(), poll() can be readily emulated in terms
of select() -- which is how this function is implemented.
REFERENCES
Stevens, W. Richard. Unix Network Programming. Prentice-Hall, 1990.
NOTES
1. This software requires an ANSI C compiler.
LICENSE
This software is released under the following BSD license, adapted from
http://opensource.org/licenses/bsd-license.php
Copyright (c) 1995-2011, Brian M. Clapper
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
* 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.
* Neither the name of the clapper.org nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER OR
CONTRIBUTORS 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.
\*---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------*\
Includes
\*---------------------------------------------------------------------------*/
#ifdef HAVE_DIX_CONFIG_H
#include <dix-config.h>
#endif
#include <unistd.h> /* standard Unix definitions */
#include <sys/types.h> /* system types */
#include <sys/time.h> /* time definitions */
#include <assert.h> /* assertion macros */
#include <string.h> /* string functions */
#include "xserver_poll.h"
/*---------------------------------------------------------------------------*\
Macros
\*---------------------------------------------------------------------------*/
#ifndef MAX
#define MAX(a,b) ((a) > (b) ? (a) : (b))
#endif
/*---------------------------------------------------------------------------*\
Private Functions
\*---------------------------------------------------------------------------*/
static int map_poll_spec
(struct pollfd *pArray,
nfds_t n_fds,
fd_set *pReadSet,
fd_set *pWriteSet,
fd_set *pExceptSet)
{
register nfds_t i; /* loop control */
register struct pollfd *pCur; /* current array element */
register int max_fd = -1; /* return value */
/*
Map the poll() structures into the file descriptor sets required
by select().
*/
for (i = 0, pCur = pArray; i < n_fds; i++, pCur++)
{
/* Skip any bad FDs in the array. */
if (pCur->fd < 0)
continue;
if (pCur->events & POLLIN)
{
/* "Input Ready" notification desired. */
FD_SET (pCur->fd, pReadSet);
}
if (pCur->events & POLLOUT)
{
/* "Output Possible" notification desired. */
FD_SET (pCur->fd, pWriteSet);
}
if (pCur->events & POLLPRI)
{
/*
"Exception Occurred" notification desired. (Exceptions
include out of band data.
*/
FD_SET (pCur->fd, pExceptSet);
}
max_fd = MAX (max_fd, pCur->fd);
}
return max_fd;
}
static struct timeval *map_timeout
(int poll_timeout, struct timeval *pSelTimeout)
{
struct timeval *pResult;
/*
Map the poll() timeout value into a select() timeout. The possible
values of the poll() timeout value, and their meanings, are:
VALUE MEANING
-1 wait indefinitely (until signal occurs)
0 return immediately, don't block
>0 wait specified number of milliseconds
select() uses a "struct timeval", which specifies the timeout in
seconds and microseconds, so the milliseconds value has to be mapped
accordingly.
*/
assert (pSelTimeout != (struct timeval *) NULL);
switch (poll_timeout)
{
case -1:
/*
A NULL timeout structure tells select() to wait indefinitely.
*/
pResult = (struct timeval *) NULL;
break;
case 0:
/*
"Return immediately" (test) is specified by all zeros in
a timeval structure.
*/
pSelTimeout->tv_sec = 0;
pSelTimeout->tv_usec = 0;
pResult = pSelTimeout;
break;
default:
/* Wait the specified number of milliseconds. */
pSelTimeout->tv_sec = poll_timeout / 1000; /* get seconds */
poll_timeout %= 1000; /* remove seconds */
pSelTimeout->tv_usec = poll_timeout * 1000; /* get microseconds */
pResult = pSelTimeout;
break;
}
return pResult;
}
static void map_select_results
(struct pollfd *pArray,
unsigned long n_fds,
fd_set *pReadSet,
fd_set *pWriteSet,
fd_set *pExceptSet)
{
register unsigned long i; /* loop control */
register struct pollfd *pCur; /* current array element */
for (i = 0, pCur = pArray; i < n_fds; i++, pCur++)
{
/* Skip any bad FDs in the array. */
if (pCur->fd < 0)
continue;
/* Exception events take priority over input events. */
pCur->revents = 0;
if (FD_ISSET (pCur->fd, pExceptSet))
pCur->revents |= POLLPRI;
else if (FD_ISSET (pCur->fd, pReadSet))
pCur->revents |= POLLIN;
if (FD_ISSET (pCur->fd, pWriteSet))
pCur->revents |= POLLOUT;
}
return;
}
/*---------------------------------------------------------------------------*\
Public Functions
\*---------------------------------------------------------------------------*/
int xserver_poll
(struct pollfd *pArray, unsigned long n_fds, int timeout)
{
fd_set read_descs; /* input file descs */
fd_set write_descs; /* output file descs */
fd_set except_descs; /* exception descs */
struct timeval stime; /* select() timeout value */
int ready_descriptors; /* function result */
int max_fd; /* maximum fd value */
struct timeval *pTimeout; /* actually passed */
FD_ZERO (&read_descs);
FD_ZERO (&write_descs);
FD_ZERO (&except_descs);
assert (pArray != (struct pollfd *) NULL);
/* Map the poll() file descriptor list in the select() data structures. */
max_fd = map_poll_spec (pArray, n_fds,
&read_descs, &write_descs, &except_descs);
/* Map the poll() timeout value in the select() timeout structure. */
pTimeout = map_timeout (timeout, &stime);
/* Make the select() call. */
ready_descriptors = select (max_fd + 1, &read_descs, &write_descs,
&except_descs, pTimeout);
if (ready_descriptors >= 0)
{
map_select_results (pArray, n_fds,
&read_descs, &write_descs, &except_descs);
}
return ready_descriptors;
}
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