poll.c

/*****************************************************************************
 * poll.c: poll() emulation
 *****************************************************************************
 * Copyright © 2007-2012 Rémi Denis-Courmont
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
 *****************************************************************************/

#ifdef HAVE_CONFIG_H
# include <config.h>
#endif

#include <stdlib.h>
#include <string.h>
#include <errno.h>

#ifdef _WIN32
# ifdef FD_SETSIZE
/* Too late for #undef FD_SETSIZE to work: fd_set is already defined. */
#  error Header inclusion order compromised!
# endif
# define FD_SETSIZE 0
# include <winsock2.h>
#else
# include <sys/time.h>
# include <sys/select.h>
#endif

int (poll) (struct pollfd *fds, unsigned nfds, int timeout)
{
#ifdef _WIN32
    size_t setsize = sizeof (fd_set) + nfds * sizeof (SOCKET);
    fd_set *rdset = malloc (setsize);
    fd_set *wrset = malloc (setsize);
    fd_set *exset = malloc (setsize);

    if (rdset == NULL || wrset == NULL || exset == NULL)
    {
        free (rdset);
        free (wrset);
        free (exset);
        errno = ENOMEM;
        return -1;
    }
/* Winsock FD_SET uses FD_SETSIZE in its expansion */
# undef FD_SETSIZE
# define FD_SETSIZE (nfds)
#else
    fd_set rdset[1], wrset[1], exset[1];
#endif
    struct timeval tv = { 0, 0 };
    int val = -1;

    FD_ZERO (rdset);
    FD_ZERO (wrset);
    FD_ZERO (exset);
    for (unsigned i = 0; i < nfds; i++)
    {
        int fd = fds[i].fd;
        if (val < fd)
            val = fd;

        /* With POSIX, FD_SET & FD_ISSET are not defined if fd is negative or
         * bigger or equal than FD_SETSIZE. That is one of the reasons why VLC
         * uses poll() rather than select(). Most POSIX systems implement
         * fd_set has a bit field with no sanity checks. This is especially bad
         * on systems (such as BSD) that have no process open files limit by
         * default, such that it is quite feasible to get fd >= FD_SETSIZE.
         * The next instructions will result in a buffer overflow if run on
         * a POSIX system, and the later FD_ISSET would perform an undefined
         * memory read.
         *
         * With Winsock, fd_set is a table of integers. This is awfully slow.
         * However, FD_SET and FD_ISSET silently and safely discard excess
         * entries. Here, overflow cannot happen anyway: fd_set of adequate
         * size are allocated.
         * Note that Vista has a much nicer WSAPoll(), but Mingw does not
         * support it yet.
         */
#ifndef _WIN32
        if ((unsigned)fd >= FD_SETSIZE)
        {
            errno = EINVAL;
            return -1;
        }
#endif
        if (fds[i].events & POLLIN)
            FD_SET (fd, rdset);
        if (fds[i].events & POLLOUT)
            FD_SET (fd, wrset);
        if (fds[i].events & POLLPRI)
            FD_SET (fd, exset);
    }

    if (timeout >= 0)
    {
        div_t d = div (timeout, 1000);
        tv.tv_sec = d.quot;
        tv.tv_usec = d.rem * 1000;
    }

    val = select (val + 1, rdset, wrset, exset,
                  (timeout >= 0) ? &tv : NULL);
    if (val == -1)
        return -1;

    for (unsigned i = 0; i < nfds; i++)
    {
        int fd = fds[i].fd;
        fds[i].revents = (FD_ISSET (fd, rdset) ? POLLIN : 0)
                       | (FD_ISSET (fd, wrset) ? POLLOUT : 0)
                       | (FD_ISSET (fd, exset) ? POLLPRI : 0);
    }
#ifdef _WIN32
    free (exset);
    free (wrset);
    free (rdset);
#endif
    return val;
}