src/win32/poll.c

   1 /*****************************************************************************
   2  * poll.c: poll() emulation for Winsock
   3  *****************************************************************************
   4  * Copyright © 2007 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 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 General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, 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 #include <vlc_common.h>
  30
  31 #ifdef FD_SETSIZE
  32 /* Too late for #undef FD_SETSIZE to work: fd_set is already defined. */
  33 # error Header inclusion order compromised!
  34 #endif
  35 #define FD_SETSIZE 0
  36 #include <vlc_network.h>
  37
  38 #ifdef __OS2__
  39 #include <sys/time.h>
  40 #include <sys/select.h>
  41 #define SOCKET unsigned
  42 #endif
  43
  44 int vlc_poll (struct pollfd *fds, unsigned nfds, int timeout)
  45 {
  46     size_t setsize = sizeof (fd_set) + nfds * sizeof (SOCKET);
  47     fd_set *rdset = malloc (setsize);
  48     fd_set *wrset = malloc (setsize);
  49     fd_set *exset = malloc (setsize);
  50     struct timeval tv = { 0, 0 };
  51     int val;
  52
  53     if (unlikely(rdset == NULL || wrset == NULL || exset == NULL))
  54     {
  55         free (rdset);
  56         free (wrset);
  57         free (exset);
  58         errno = ENOMEM;
  59         return -1;
  60     }
  61
  62 /* Winsock FD_SET uses FD_SETSIZE in its expansion */
  63 #undef FD_SETSIZE
  64 #define FD_SETSIZE (nfds)
  65
  66 resume:
  67     val = -1;
  68     vlc_testcancel ();
  69
  70     FD_ZERO (rdset);
  71     FD_ZERO (wrset);
  72     FD_ZERO (exset);
  73     for (unsigned i = 0; i < nfds; i++)
  74     {
  75         int fd = fds[i].fd;
  76         if (val < fd)
  77             val = fd;
  78
  79         /* With POSIX, FD_SET & FD_ISSET are not defined if fd is negative or
  80          * bigger or equal than FD_SETSIZE. That is one of the reasons why VLC
  81          * uses poll() rather than select(). Most POSIX systems implement
  82          * fd_set has a bit field with no sanity checks. This is especially bad
  83          * on systems (such as BSD) that have no process open files limit by
  84          * default, such that it is quite feasible to get fd >= FD_SETSIZE.
  85          * The next instructions will result in a buffer overflow if run on
  86          * a POSIX system, and the later FD_ISSET would perform an undefined
  87          * memory read.
  88          *
  89          * With Winsock, fd_set is a table of integers. This is awfully slow.
  90          * However, FD_SET and FD_ISSET silently and safely discard excess
  91          * entries. Here, overflow cannot happen anyway: fd_set of adequate
  92          * size are allocated.
  93          * Note that Vista has a much nicer WSAPoll(), but Mingw does not
  94          * support it yet.
  95          */
  96         if (fds[i].events & POLLIN)
  97             FD_SET ((SOCKET)fd, rdset);
  98         if (fds[i].events & POLLOUT)
  99             FD_SET ((SOCKET)fd, wrset);
 100         if (fds[i].events & POLLPRI)
 101             FD_SET ((SOCKET)fd, exset);
 102     }
 103
 104 #ifndef HAVE_ALERTABLE_SELECT
 105 # warning FIXME! Fix cancellation and remove this crap.
 106     if ((timeout < 0) || (timeout > 50))
 107     {
 108         tv.tv_sec = 0;
 109         tv.tv_usec = 50000;
 110     }
 111     else
 112 #endif
 113     if (timeout >= 0)
 114     {
 115         div_t d = div (timeout, 1000);
 116         tv.tv_sec = d.quot;
 117         tv.tv_usec = d.rem * 1000;
 118     }
 119
 120     val = select (val + 1, rdset, wrset, exset,
 121                   /*(timeout >= 0) ?*/ &tv /*: NULL*/);
 122
 123 #ifndef HAVE_ALERTABLE_SELECT
 124     if (val == 0)
 125     {
 126         if (timeout > 0)
 127             timeout -= (timeout > 50) ? 50 : timeout;
 128         if (timeout != 0)
 129             goto resume;
 130     }
 131 #endif
 132
 133     if (val == -1)
 134         return -1;
 135
 136     for (unsigned i = 0; i < nfds; i++)
 137     {
 138         int fd = fds[i].fd;
 139         fds[i].revents = (FD_ISSET (fd, rdset) ? POLLIN : 0)
 140                        | (FD_ISSET (fd, wrset) ? POLLOUT : 0)
 141                        | (FD_ISSET (fd, exset) ? POLLPRI : 0);
 142     }
 143     free (exset);
 144     free (wrset);
 145     free (rdset);
 146     return val;
 147 }