compat/poll.c

   1 /*****************************************************************************
   2  * poll.c: poll() emulation
   3  *****************************************************************************
   4  * Copyright © 2007-2012 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  19  *****************************************************************************/
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24
  25 #include <stdlib.h>
  26 #include <string.h>
  27 #include <errno.h>
  28
  29 #ifdef _WIN32
  30 # ifdef FD_SETSIZE
  31 /* Too late for #undef FD_SETSIZE to work: fd_set is already defined. */
  32 #  error Header inclusion order compromised!
  33 # endif
  34 # define FD_SETSIZE 0
  35 # include <winsock2.h>
  36 #else
  37 # include <sys/time.h>
  38 # include <sys/select.h>
  39 #endif
  40
  41 int (poll) (struct pollfd *fds, unsigned nfds, int timeout)
  42 {
  43 #ifdef _WIN32
  44     size_t setsize = sizeof (fd_set) + nfds * sizeof (SOCKET);
  45     fd_set *rdset = malloc (setsize);
  46     fd_set *wrset = malloc (setsize);
  47     fd_set *exset = malloc (setsize);
  48
  49     if (rdset == NULL || wrset == NULL || exset == NULL)
  50     {
  51         free (rdset);
  52         free (wrset);
  53         free (exset);
  54         errno = ENOMEM;
  55         return -1;
  56     }
  57 /* Winsock FD_SET uses FD_SETSIZE in its expansion */
  58 # undef FD_SETSIZE
  59 # define FD_SETSIZE (nfds)
  60 #else
  61     fd_set rdset[1], wrset[1], exset[1];
  62 #endif
  63     struct timeval tv = { 0, 0 };
  64     int val = -1;
  65
  66     FD_ZERO (rdset);
  67     FD_ZERO (wrset);
  68     FD_ZERO (exset);
  69     for (unsigned i = 0; i < nfds; i++)
  70     {
  71         int fd = fds[i].fd;
  72         if (val < fd)
  73             val = fd;
  74
  75         /* With POSIX, FD_SET & FD_ISSET are not defined if fd is negative or
  76          * bigger or equal than FD_SETSIZE. That is one of the reasons why VLC
  77          * uses poll() rather than select(). Most POSIX systems implement
  78          * fd_set has a bit field with no sanity checks. This is especially bad
  79          * on systems (such as BSD) that have no process open files limit by
  80          * default, such that it is quite feasible to get fd >= FD_SETSIZE.
  81          * The next instructions will result in a buffer overflow if run on
  82          * a POSIX system, and the later FD_ISSET would perform an undefined
  83          * memory read.
  84          *
  85          * With Winsock, fd_set is a table of integers. This is awfully slow.
  86          * However, FD_SET and FD_ISSET silently and safely discard excess
  87          * entries. Here, overflow cannot happen anyway: fd_set of adequate
  88          * size are allocated.
  89          * Note that Vista has a much nicer WSAPoll(), but Mingw does not
  90          * support it yet.
  91          */
  92 #ifndef _WIN32
  93         if ((unsigned)fd >= FD_SETSIZE)
  94         {
  95             errno = EINVAL;
  96             return -1;
  97         }
  98 #endif
  99         if (fds[i].events & POLLIN)
 100             FD_SET (fd, rdset);
 101         if (fds[i].events & POLLOUT)
 102             FD_SET (fd, wrset);
 103         if (fds[i].events & POLLPRI)
 104             FD_SET (fd, exset);
 105     }
 106
 107     if (timeout >= 0)
 108     {
 109         div_t d = div (timeout, 1000);
 110         tv.tv_sec = d.quot;
 111         tv.tv_usec = d.rem * 1000;
 112     }
 113
 114     val = select (val + 1, rdset, wrset, exset,
 115                   (timeout >= 0) ? &tv : NULL);
 116     if (val == -1)
 117         return -1;
 118
 119     for (unsigned i = 0; i < nfds; i++)
 120     {
 121         int fd = fds[i].fd;
 122         fds[i].revents = (FD_ISSET (fd, rdset) ? POLLIN : 0)
 123                        | (FD_ISSET (fd, wrset) ? POLLOUT : 0)
 124                        | (FD_ISSET (fd, exset) ? POLLPRI : 0);
 125     }
 126 #ifdef _WIN32
 127     free (exset);
 128     free (wrset);
 129     free (rdset);
 130 #endif
 131     return val;
 132 }