src/xgselect.c

   1 /* Function for handling the GLib event loop.
   2
   3 Copyright (C) 2009-2016 Free Software Foundation, Inc.
   4
   5 This file is part of GNU Emacs.
   6
   7 GNU Emacs is free software: you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation, either version 3 of the License, or (at
  10 your option) any later version.
  11
  12 GNU Emacs is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include <config.h>
  21
  22 #include "xgselect.h"
  23
  24 #ifdef HAVE_GLIB
  25
  26 #include <glib.h>
  27 #include <errno.h>
  28 #include "blockinput.h"
  29 #include "systime.h"
  30
  31 /* `xg_select' is a `pselect' replacement.  Why do we need a separate function?
  32    1. Timeouts.  Glib and Gtk rely on timer events.  If we did pselect
  33       with a greater timeout then the one scheduled by Glib, we would
  34       not allow Glib to process its timer events.  We want Glib to
  35       work smoothly, so we need to reduce our timeout to match Glib.
  36    2. Descriptors.  Glib may listen to more file descriptors than we do.
  37       So we add Glib descriptors to our pselect pool, but we don't change
  38       the value returned by the function.  The return value  matches only
  39       the descriptors passed as arguments, making it compatible with
  40       plain pselect.  */
  41
  42 int
  43 xg_select (int fds_lim, fd_set *rfds, fd_set *wfds, fd_set *efds,
  44            struct timespec const *timeout, sigset_t const *sigmask)
  45 {
  46   fd_set all_rfds, all_wfds;
  47   struct timespec tmo;
  48   struct timespec const *tmop = timeout;
  49
  50   GMainContext *context;
  51   bool have_wfds = wfds != NULL;
  52   GPollFD gfds_buf[128];
  53   GPollFD *gfds = gfds_buf;
  54   int gfds_size = ARRAYELTS (gfds_buf);
  55   int n_gfds, retval = 0, our_fds = 0, max_fds = fds_lim - 1;
  56   bool context_acquired = false;
  57   int i, nfds, tmo_in_millisec;
  58   bool need_to_dispatch;
  59   USE_SAFE_ALLOCA;
  60
  61   context = g_main_context_default ();
  62   context_acquired = g_main_context_acquire (context);
  63   /* FIXME: If we couldn't acquire the context, we just silently proceed
  64      because this function handles more than just glib file descriptors.
  65      Note that, as implemented, this failure is completely silent: there is
  66      no feedback to the caller.  */
  67
  68   if (rfds) all_rfds = *rfds;
  69   else FD_ZERO (&all_rfds);
  70   if (wfds) all_wfds = *wfds;
  71   else FD_ZERO (&all_wfds);
  72
  73   n_gfds = (context_acquired
  74             ? g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
  75                                     gfds, gfds_size)
  76             : -1);
  77
  78   if (gfds_size < n_gfds)
  79     {
  80       SAFE_NALLOCA (gfds, sizeof *gfds, n_gfds);
  81       gfds_size = n_gfds;
  82       n_gfds = g_main_context_query (context, G_PRIORITY_LOW, &tmo_in_millisec,
  83                                      gfds, gfds_size);
  84     }
  85
  86   for (i = 0; i < n_gfds; ++i)
  87     {
  88       if (gfds[i].events & G_IO_IN)
  89         {
  90           FD_SET (gfds[i].fd, &all_rfds);
  91           if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
  92         }
  93       if (gfds[i].events & G_IO_OUT)
  94         {
  95           FD_SET (gfds[i].fd, &all_wfds);
  96           if (gfds[i].fd > max_fds) max_fds = gfds[i].fd;
  97           have_wfds = true;
  98         }
  99     }
 100
 101   SAFE_FREE ();
 102
 103   if (n_gfds >= 0 && tmo_in_millisec >= 0)
 104     {
 105       tmo = make_timespec (tmo_in_millisec / 1000,
 106                            1000 * 1000 * (tmo_in_millisec % 1000));
 107       if (!timeout || timespec_cmp (tmo, *timeout) < 0)
 108         tmop = &tmo;
 109     }
 110
 111   fds_lim = max_fds + 1;
 112   nfds = pselect (fds_lim, &all_rfds, have_wfds ? &all_wfds : NULL,
 113                   efds, tmop, sigmask);
 114
 115   if (nfds < 0)
 116     retval = nfds;
 117   else if (nfds > 0)
 118     {
 119       for (i = 0; i < fds_lim; ++i)
 120         {
 121           if (FD_ISSET (i, &all_rfds))
 122             {
 123               if (rfds && FD_ISSET (i, rfds)) ++retval;
 124               else ++our_fds;
 125             }
 126           else if (rfds)
 127             FD_CLR (i, rfds);
 128
 129           if (have_wfds && FD_ISSET (i, &all_wfds))
 130             {
 131               if (wfds && FD_ISSET (i, wfds)) ++retval;
 132               else ++our_fds;
 133             }
 134           else if (wfds)
 135             FD_CLR (i, wfds);
 136
 137           if (efds && FD_ISSET (i, efds))
 138             ++retval;
 139         }
 140     }
 141
 142   /* If Gtk+ is in use eventually gtk_main_iteration will be called,
 143      unless retval is zero.  */
 144 #ifdef USE_GTK
 145   need_to_dispatch = retval == 0;
 146 #else
 147   need_to_dispatch = true;
 148 #endif
 149   if (need_to_dispatch)
 150     {
 151       int pselect_errno = errno;
 152       /* Prevent g_main_dispatch recursion, that would occur without
 153          block_input wrapper, because event handlers call
 154          unblock_input.  Event loop recursion was causing Bug#15801.  */
 155       block_input ();
 156       while (g_main_context_pending (context))
 157         g_main_context_dispatch (context);
 158       unblock_input ();
 159       errno = pselect_errno;
 160     }
 161
 162   if (context_acquired)
 163     g_main_context_release (context);
 164
 165   /* To not have to recalculate timeout, return like this.  */
 166   if ((our_fds > 0 || (nfds == 0 && tmop == &tmo)) && (retval == 0))
 167     {
 168       retval = -1;
 169       errno = EINTR;
 170     }
 171
 172   return retval;
 173 }
 174 #endif /* HAVE_GLIB */